16.4 Kidneys
Kidneys on the Menu
Pictured in Figure 16.4.1 is a steak and kidney pie; this savory dish is a British favorite. When kidneys are on a menu, they typically come from sheep, pigs, or cows. In these animals (as in the human animal), kidneys are the main organs of excretion.
Location of the Kidneys
The two bean-shaped are located high in the back of the , one on each side of the spine. Both kidneys sit just below the , the large breathing muscle that separates the abdominal and thoracic cavities. As you can see in the following figure, the right kidney is slightly smaller and lower than the left kidney. The right kidney is behind the , and the left kidney is behind the . The location of the liver explains why the right kidney is smaller and lower than the left.
Kidney Anatomy
The shape of each kidney gives it a convex side (curving outward) and a concave side (curving inward). You can see this clearly in the detailed diagram of kidney anatomy shown in Figure 16.4.3. The concave side is where the renal artery enters the kidney, as well as where the renal vein and ureter leave the kidney. This area of the kidney is called the . The entire kidney is surrounded by tough fibrous tissue — called the — which, in turn, is surrounded by two layers of protective, cushioning fat.
Internally, each kidney is divided into two major layers: the outer and the inner (see Figure 16.4.3 above). These layers take the shape of many cone-shaped renal lobules, each containing renal cortex surrounding a portion of medulla called a . Within the renal pyramids are the structural and functional units of the kidneys, the tiny . Between the renal pyramids are projections of cortex called . The tip, or papilla, of each pyramid empties urine into a minor calyx (chamber). Several minor calyces empty into a major calyx, and the latter empty into the funnel-shaped cavity called the , which becomes the ureter as it leaves the kidney.
Renal Circulation
The renal circulation is an important part of the kidney’s primary function of filtering waste products from the blood. is supplied to the kidneys via the renal arteries. The right renal artery supplies the right kidney, and the left renal artery supplies the left kidney. These two arteries branch directly from the aorta, which is the largest artery in the body. Each kidney is only about 11 cm (4.4 in) long, and has a mass of just 150 grams (5.3 oz), yet it receives about ten per cent of the total output of blood from the heart. Blood is filtered through the kidneys every 3 minutes, 24 hours a day, every day of your life.
As indicated in Figure 16.4.4, each renal artery carries blood with waste products into the kidney. Within the kidney, the renal artery branches into increasingly smaller that extend through the between the . These arteries, in turn, branch into arterioles that penetrate the renal pyramids. Blood in the arterioles passes through , the structures that actually filter the blood. After blood passes through the nephrons and is filtered, the clean blood moves through a network of venules that converge into small . Small veins merge into increasingly larger ones, and ultimately into the renal vein, which carries clean blood away from the kidney to the inferior .
Nephron Structure and Function
Figure 16.4.4 gives an indication of the complex structure of a nephron. The is the basic structural and functional unit of the kidney, and each kidney typically contains at least a million of them. As blood flows through a nephron, many materials are filtered out of the blood, needed materials are returned to the blood, and the remaining materials form urine. Most of the waste products removed from the blood and excreted in urine are byproducts of . At least half of the waste is , a waste product produced by . Another important waste is , produced in catabolism.
Components of a Nephron
Figure 16.4.5 shows in greater detail the components of a . Each nephron is composed of an initial filtering component that consists of a network of capillaries called the (plural, glomeruli), which is surrounded by a space within a structure called (also known as the Bowman’s capsule). Extending from glomerular capsule is the . The proximal end (nearest glomerular capsule) of the renal tubule is called the . From here, the renal tubule continues as a loop (known as the ) (also known as the loop of the nephron), which in turn becomes the . The latter finally joins with a collecting duct. As you can see in the diagram, arterioles surround the total length of the renal tubule in a mesh called the .
Function of a Nephron
The simplified diagram of a nephron in Figure 16.4.6 shows an overview of how the nephron functions. Blood enters the nephron through an arteriole called the afferent arteriole. Next, some of the blood passes through the capillaries of the glomerulus. Any blood that doesn’t pass through the glomerulus — as well as blood after it passes through the glomerular capillaries — continues on through an arteriole called the efferent arteriole. The efferent arteriole follows the renal tubule of the nephron, where it continues playing a role in nephron functioning.
Filtration
As blood from the afferent arteriole flows through the glomerular capillaries, it is under pressure. Because of the pressure, water and solutes are filtered out of the blood and into the space made by glomerular capsule, almost like the water you cook pasta is is filtered out through a strainer. This is the filtration stage of nephron function. The filtered substances — called — pass into glomerular capsule, and from there into the proximal end of the . Anything too large to move through the pores in the glomerulus, such as blood cells, large proteins, etc., stay in the cardiovascular system. At this stage, filtrate (fluid in the nephron) includes water, salts, organic solids (such as nutrients), and waste products of metabolism (such as urea).
Reabsorption and Secretion
As filtrate moves through the renal tubule, some of the substances it contains are reabsorbed from the filtrate back into the blood in the efferent arteriole (via ). This is the reabsorption stage of nephron function and it is about returning “the good stuff” back to the blood so that it doesn’t exit the body in urine. About two-thirds of the filtered salts and water, and all of the filtered organic solutes (mainly and ) are reabsorbed from the filtrate by the blood in the peritubular capillary network. occurs mainly in the proximal convoluted tubule and the loop of Henle, as seen in Figure 16.4.7.
At the distal end of the renal tubule, some additional reabsorption generally occurs. This is also the region of the tubule where other substances from the blood are added to the filtrate in the tubule. The addition of other substances to the filtrate from the blood is called . Both reabsorption and secretion (shown in Figure 16.4.7) in the distal convoluted tubule are largely under the control of endocrine hormones that maintain of water and mineral salts in the blood. These hormones work by controlling what is reabsorbed into the blood from the filtrate and what is secreted from the blood into the filtrate to become urine. For example, causes more calcium to be reabsorbed into the blood and more phosphorus to be secreted into the filtrate.
Collection of Urine and Excretion
By the time the filtrate has passed through the entire renal tubule, it has become the liquid waste known as . Urine empties from the distal end of the into a . From there, the urine flows into increasingly larger collecting ducts. As urine flows through the system of collecting ducts, more water may be reabsorbed from it. This will occur in the presence of from the posterior . This hormone makes the collecting ducts permeable to water, allowing water molecules to pass through them into capillaries by , while preventing the passage of ions or other solutes. As much as 75% of the water may be reabsorbed from urine in the collecting ducts, making the urine more concentrated.
Urine finally exits the largest collecting ducts through the renal papillae. It empties into the renal calyces, and finally into the . From there, it travels through the to the for eventual excretion from the body. An average of roughly 1.5 litres (a little over 6 cups) of urine is excreted each day. Normally, urine is yellow or amber in colour (see Figure 16.4.8). The darker the colour, generally speaking, the more concentrated the urine is.
Besides filtering blood and forming urine for excretion of soluble wastes, the kidneys have several vital functions in maintaining body-wide . Most of these functions are related to the composition or volume of urine formed by the kidneys. The kidneys must maintain the proper balance of water and salts in the body, normal , and the correct range of blood . Through the processes of absorption and secretion by nephrons, more or less water, salt ions, acids, or bases are returned to the blood or excreted in urine, as needed, to maintain homeostasis.
Blood Pressure Regulation
The kidneys do not control homeostasis all alone. As indicated above, endocrine hormones are also involved. Consider the regulation of blood pressure by the kidneys. Blood pressure is the pressure exerted by blood on the walls of the arteries. The regulation of blood pressure is part of a complex system, called the renin-angiotensin-aldosterone system. This system regulates the concentration of sodium in the blood to control blood pressure.
The renin-angiotensin-aldosterone system is put into play when the concentration of sodium ions in the blood falls lower than normal. This causes the kidneys to secrete an enzyme called into the blood. It also causes the liver to secrete a protein called angiotensinogen. Renin changes angiotensinogen into a proto-hormone called angiotensin I. This is converted to angiotensin II by an enzyme (angiotensin-converting enzyme) in lung capillaries.
Angiotensin II is a potent hormone that causes arterioles to constrict. This, in turn, increases blood pressure. Angiotensin II also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the kidneys to increase the reabsorption of sodium ions and water from the filtrate into the blood. This returns the concentration of sodium ions in the blood to normal. The increased water in the blood also increases blood volume and blood pressure.
Other Kidney Hormones
Hormones other than renin are also produced and secreted by the kidneys. These include calcitriol and erythropoietin.
- is secreted by the kidneys in response to low levels of calcium in the blood. This hormone stimulates uptake of calcium by the intestine, thus raising blood levels of calcium.
- is secreted by the kidneys in response to low levels of oxygen in the blood. This hormone stimulates erythropoiesis, which is the production of in bone marrow. Extra red blood cells increase the level of oxygen carried in the blood.
Feature: Human Biology in the News
Kidney failure is a complication of common disorders including and . It is estimated that approximately 12.5% of Canadians have some form of kidney disease. If the disease is serious, the patient must either receive a donated kidney or have frequent hemodialysis, a medical procedure in which the blood is artificially filtered through a machine. Transplant generally results in better outcomes than hemodialysis, but demand for organs far outstrips the supply. The average time on the organ donation waitlist for a kidney is four years. There are over 3,000 Canadians on the wait list for a kidney transplant and some will die waiting for a kidney to become available.
For the past decade, Dr. William Fissell, a kidney specialist at Vanderbilt University, has been working to create an implantable part-biological and part-artificial kidney. Using microchips like those used in computers, he has produced an artificial kidney small enough to implant in the patient’s body in place of the failed kidney. According to Dr. Fissell, the artificial kidney is “… a bio-hybrid device that can mimic a kidney to remove enough waste products, salt, and water to keep a patient off [hemo]dialysis.”
The filtration system in the artificial kidney consists of a stack of 15 microchips. Tiny pores in the microchips act as a scaffold for the growth of living kidney cells that can mimic the natural functions of the kidney. The living cells form a membrane to filter the patient’s blood as a biological kidney would, but with less risk of rejection by the patient’s immune system, because they are embedded within the device. The new kidney doesn’t need a power source, because it uses the natural pressure of blood flowing through arteries to push the blood through the filtration system. A major part of the design of the artificial organ was devoted to fine tuning the fluid dynamics so blood flows through the device without clotting.
Because of the potential life-saving benefits of the device, the implantable kidney was given fast-track approval for testing in people by the U.S. Food and Drug Administration. The artificial kidney is expected to be tested in pilot trials by 2018. Dr. Fissell says he has a long list of patients eager to volunteer for the trials.
16.4 Summary
- The two bean-shaped kidneys are located high in the back of the abdominal cavity on either side of the spine. A renal artery connects each kidney with the aorta, and transports unfiltered blood to the kidney. A renal vein connects each kidney with the inferior vena cava and transports filtered blood back to the circulation.
- The kidney has two main layers involved in the filtration of blood and formation of urine: the outer cortex and inner medulla. At least a million nephrons — which are the tiny functional units of the kidney — span the cortex and medulla. The entire kidney is surrounded by a fibrous capsule and protective fat layers.
- As blood flows through a nephron, many materials are filtered out of the blood, needed materials are returned to the blood, and the remaining materials are used to form urine.
- In each nephron, the glomerulus and surrounding Bowman’s capsule form the unit that filters blood. From Bowman’s capsule, the material filtered from blood (called filtrate) passes through the long renal tubule. As it does, some substances are reabsorbed into the blood, and other substances are secreted from the blood into the filtrate, finally forming urine. The urine empties into collecting ducts, where more water may be reabsorbed.
- The kidneys control homeostasis with the help of endocrine hormones. The kidneys, for example, are part of the renin-angiotensin-aldosterone system that regulates the concentration of sodium in the blood to control blood pressure. In this system, the enzyme renin secreted by the kidneys works with hormones from the liver and adrenal gland to stimulate nephrons to reabsorb more sodium and water from urine.
- The kidneys also secrete endocrine hormones, including calcitriol — which helps control the level of calcium in the blood — and erythropoietin, which stimulates bone marrow to produce red blood cells.
16.4 Review Questions
- Contrast the renal artery and renal vein.
- Identify the functions of a nephron. Describe in detail what happens to fluids (blood, filtrate, and urine) as they pass through the parts of a nephron.
- Identify two endocrine hormones secreted by the kidneys, along with the functions they control.
- Name two regions in the kidney where water is reabsorbed.
- Is the blood in the glomerular capillaries more or less filtered than the blood in the peritubular capillaries? Explain your answer.
- What do you think would happen if blood flow to the kidneys is blocked?
16.4 Explore More
How do your kidneys work? – Emma Bryce, TED-Ed, 2015.
https://youtu.be/es-t8lO1KpA
Urine Formation, Hamada Abass, 2013.
Printing a human kidney – Anthony Atala, TED-Ed, 2013.
Attributions
Figure 16.4.1
Steak and Kidney Pie by Charles Haynes on Flickr is used under a CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0/) license.
Figure 16.4.2
Gray Kidneys by Henry Vandyke Carter (1831-1897) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain). (Bartleby.com: Gray’s Anatomy, Plate 1120).
Figure 16.4.3
Blausen_0592_KidneyAnatomy_01 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.4
Diagram_showing_how_the_kidneys_work_CRUK_138.svg by Cancer Research UK on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 16.4.5
Blood_Flow_in_the_Nephron by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.6
1024px-Physiology_of_Nephron by Madhero88 on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.7
Nephron_Secretion_Reabsorption by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 16.4.8
Urine by User:Markhamilton at English Wikipedia on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 16.4.9
Renin_Angiotensin_System-01 by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 25.10 Blood flow in the nephron [digital image]. In Anatomy and Physiology (Section 25.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/25-3-gross-anatomy-of-the-kidney
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 25.17 Locations of secretion and reabsorption in the nephron [digital image]. In Anatomy and Physiology (Section 25.6). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/25-6-tubular-reabsorption
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 26.14 The renin-angiotensin system [digital image]. In Anatomy and Physiology (Section 26.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/26-3-electrolyte-balance
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436
Hamada Abass. (2013). Urine formation. YouTube. https://www.youtube.com/watch?v=es-t8lO1KpA&feature=youtu.be
TED-Ed. (2015, February 9). How do your kidneys work? – Emma Bryce. YouTube. https://www.youtube.com/watch?v=FN3MFhYPWWo&feature=youtu.be
TED-Ed. (2013, March 15). Printing a human kidney – Anthony Atala. YouTube. https://www.youtube.com/watch?v=bX3C201O4MA&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Seeing Your Breath
Why can you “see your breath” on a cold day? The air you exhale through your nose and mouth is warm like the inside of your body. Exhaled air also contains a lot of water vapor, because it passes over moist surfaces from the lungs to the nose or mouth. The water vapor in your breath cools suddenly when it reaches the much colder outside air. This causes the water vapor to condense into a fog of tiny droplets of liquid water. You release water vapor and other gases from your body through the process of respiration.
What is Respiration?
is the life-sustaining process in which gases are exchanged between the body and the outside atmosphere. Specifically, oxygen moves from the outside air into the body; and water vapor, carbon dioxide, and other waste gases move from inside the body to the outside air. Respiration is carried out mainly by the . It is important to note that respiration by the respiratory system is not the same process as —which occurs inside cells — although the two processes are closely connected. Cellular respiration is the metabolic process in which cells obtain energy, usually by “burning” glucose in the presence of oxygen. When cellular respiration is , it uses oxygen and releases carbon dioxide as a waste product. Respiration by the respiratory system supplies the oxygen needed by cells for aerobic cellular respiration, and removes the carbon dioxide produced by cells during cellular respiration.
Respiration by the respiratory system actually involves two subsidiary processes. One process is , or breathing. Ventilation is the physical process of conducting air to and from the lungs. The other process is . This is the biochemical process in which oxygen diffuses out of the air and into the blood, while carbon dioxide and other waste gases diffuse out of the blood and into the air. All of the organs of the respiratory system are involved in breathing, but only the lungs are involved in gas exchange.
Respiratory Organs
The organs of the respiratory system form a continuous system of passages, called the , through which air flows into and out of the body. The respiratory tract has two major divisions: the and the . The organs in each division are shown in Figure 13.2.2. In addition to these organs, certain muscles of the thorax (body cavity that fills the chest) are also involved in respiration by enabling breathing. Most important is a large muscle called the , which lies below the lungs and separates the thorax from the abdomen. Smaller muscles between the ribs also play a role in breathing.
Upper Respiratory Tract
All of the organs and other structures of the upper respiratory tract are involved in , or the movement of air into and out of the body. Upper respiratory tract organs provide a route for air to move between the outside atmosphere and the lungs. They also clean, humidify, and warm the incoming air. No gas exchange occurs in these organs.
Nasal Cavity
The is a large, air-filled space in the above and behind the nose in the middle of the face. It is a continuation of the two nostrils. As inhaled air flows through the nasal cavity, it is warmed and humidified by blood vessels very close to the surface of this epithelial tissue . Hairs in the nose and mucous produced by help trap larger foreign particles in the air before they go deeper into the respiratory tract. In addition to its respiratory functions, the nasal cavity also contains s needed for sense of smellno post, and contribution to the sense of .
Pharynx
The is a tube-like structure that connects the nasal cavity and the back of the to other structures lower in the throat, including the larynx. The pharynx has dual functions — both air and food (or other swallowed substances) pass through it, so it is part of both the respiratory and the digestive systems. Air passes from the nasal cavity through the pharynx to the larynx (as well as in the opposite direction). Food passes from the mouth through the pharynx to the esophagus.
Larynx
The connects the pharynx and trachea, and helps to conduct air through the respiratory tract. The larynx is also called the , because it contains the , which vibrate when air flows over them, thereby producing sound. You can see the vocal cords in the larynx in Figures 13.2.3 and 13.2.4. Certain muscles in the larynx move the vocal cords apart to allow breathing. Other muscles in the larynx move the vocal cords together to allow the production of vocal sounds. The latter muscles also control the pitch of sounds and help control their volume.
Figure 13.2.4 The larynx as viewed from the top. |
A very important function of the larynx is protecting the trachea from aspirated food. When swallowing occurs, the backward motion of the tongue forces a flap called the to close over the entrance to the larynx. (You can see the epiglottis in both Figure 13.2.3 and 13.2.4.) This prevents swallowed material from entering the larynx and moving deeper into the respiratory tract. If swallowed material does start to enter the larynx, it irritates the larynx and stimulates a strong cough reflex. This generally expels the material out of the larynx, and into the throat.
https://www.youtube.com/watch?v=BsyB88mq5rQ
Larynx Model - Respiratory System, Dr. Lotz, 2018.
Lower Respiratory Tract
The trachea and other passages of the lower respiratory tract conduct air between the upper respiratory tract and the lungs. These passages form an inverted tree-like shape (Figure 13.2.5), with repeated branching as they move deeper into the lungs. All told, there are an astonishing 2,414 kilometres (1,500 miles) of airways conducting air through the human respiratory tract! It is only in the lungs, however, that gas exchange occurs between the air and the bloodstream.
Trachea
The , or windpipe, is the widest passageway in the respiratory tract. It is about 2.5 cm wide and 10-15 cm long (approximately 1 inch wide and 4–6 inches long). It is formed by rings of cartilage, which make it relatively strong and resilient. The trachea connects the larynx to the lungs for the passage of air through the respiratory tract. The trachea branches at the bottom to form two bronchial tubes.
Bronchi and Bronchioles
There are two main bronchial tubes, or (singular, bronchus), called the right and left bronchi. The bronchi carry air between the trachea and lungs. Each bronchus branches into smaller, secondary bronchi; and secondary bronchi branch into still smaller tertiary bronchi. The smallest bronchi branch into very small tubules called s. The tiniest bronchioles end in alveolar ducts, which terminate in clusters of minuscule air sacs, called (singular, alveolus), in the lungs.
Lungs
The are the largest organs of the respiratory tract. They are suspended within the pleural cavity of the thorax. The lungs are surrounded by two thin membranes called , which secrete fluid that allows the lungs to move freely within the pleural cavity. This is necessary so the lungs can expand and contract during breathing. In Figure 13.2.6, you can see that each of the two lungs is divided into sections. These are called lobes, and they are separated from each other by connective tissues. The right lung is larger and contains three lobes. The left lung is smaller and contains only two lobes. The smaller left lung allows room for the heart, which is just left of the center of the chest.
As mentioned previously, the bronchi terminate in bronchioles which feed air into alveoli, tiny sacs of simple squamous epithelial tissue which make up the bulk of the lung. The cross-section of lung tissue in the diagram below (Figure 13.2.7) shows the alveoli, in which gas exchange takes place with the capillary network that surrounds them.
Lung tissue consists mainly of (see Figures 13.2.7 and 13.2.8). These tiny air sacs are the functional units of the lungs where gas exchange takes place. The two lungs may contain as many as 700 million alveoli, providing a huge total surface area for gas exchange to take place. In fact, alveoli in the two lungs provide as much surface area as half a tennis court! Each time you breathe in, the alveoli fill with air, making the lungs expand. Oxygen in the air inside the alveoli is absorbed by the blood via diffusion in the mesh-like network of tiny capillaries that surrounds each alveolus. The blood in these capillaries also releases carbon dioxide (also by diffusion) into the air inside the alveoli. Each time you breathe out, air leaves the alveoli and rushes into the outside atmosphere, carrying waste gases with it.
The lungs receive blood from two major sources. They receive deoxygenated blood from the right side of the heart. This blood absorbs oxygen in the lungs and carries it back to the left side heart to be pumped to cells throughout the body. The lungs also receive oxygenated blood from the heart that provides oxygen to the cells of the lungs for cellular respiration.
Protecting the Respiratory System
You may be able to survive for weeks without food and for days without water, but you can survive without oxygen for only a matter of minutes — except under exceptional circumstances — so protecting the respiratory system is vital. Ensuring that a patient has an open airway is the first step in treating many medical emergencies. Fortunately, the respiratory system is well protected by the of the skeletal system. The extensive surface area of the respiratory system, however, is directly exposed to the outside world and all its potential dangers in inhaled air. It should come as no surprise that the respiratory system has a variety of ways to protect itself from harmful substances, such as dust and pathogens in the air.
The main way the respiratory system protects itself is called the . From the nose through the bronchi, the respiratory tract is covered in epithelium that contains mucus-secreting goblet cells. The mucus traps particles and pathogens in the incoming air. The epithelium of the respiratory tract is also covered with tiny cell projections called (singular, cilium), as shown in the animation. The cilia constantly move in a sweeping motion upward toward the throat, moving the mucus and trapped particles and pathogens away from the lungs and toward the outside of the body. The upward sweeping motion of cilia lining the respiratory tract helps keep it free from dust, pathogens, and other harmful substances.
Watch "Mucociliary clearance" by I-Hsun Wu to learn more:
https://www.youtube.com/watch?v=HMB6flEaZwI
Mucociliary clearance, I-Hsun Wu, 2015.
Sneezing is a similar involuntary response that occurs when nerves lining the nasal passage are irritated. It results in forceful expulsion of air from the mouth, which sprays millions of tiny droplets of mucus and other debris out of the mouth and into the air, as shown in Figure 13.2.9. This explains why it is so important to sneeze into a tissue (rather than the air) if we are to prevent the transmission of respiratory pathogens.
How the Respiratory System Works with Other Organ Systems
The amount of oxygen and carbon dioxide in the blood must be maintained within a limited range for survival of the organism. Cells cannot survive for long without oxygen, and if there is too much carbon dioxide in the blood, the blood becomes dangerously (pH is too low). Conversely, if there is too little carbon dioxide in the blood, the blood becomes too basic (pH is too high). The respiratory system works hand-in-hand with the and systems to maintain in blood gases and pH.
It is the level of carbon dioxide — rather than the level of oxygen — that is most closely monitored to maintain blood gas and pH homeostasis. The level of carbon dioxide in the blood is detected by cells in the , which speed up or slow down the rate of breathing through the autonomic nervous system as needed to bring the carbon dioxide level within the normal range. Faster breathing lowers the carbon dioxide level (and raises the oxygen level and pH), while slower breathing has the opposite effects. In this way, the levels of carbon dioxide, oxygen, and pH are maintained within normal limits.
The respiratory system also works closely with the cardiovascular system to maintain homeostasis. The respiratory system exchanges gases with the outside air, but it needs the cardiovascular system to carry them to and from body cells. Oxygen is absorbed by the blood in the lungs and then transported through a vast network of blood vessels to cells throughout the body, where it is needed for aerobic cellular respiration. The same system absorbs carbon dioxide from cells and carries it to the respiratory system for removal from the body.
Feature: My Human Body
Choking due to a foreign object becoming lodged in the airway results in nearly 5 thousand deaths in Canada each year. In addition, choking accounts for almost 40% of unintentional injuries in infants under the age of one. For the sake of your own human body, as well as those of loved ones, you should be aware of choking risks, signs, and treatments.
Choking is the mechanical obstruction of the flow of air from the atmosphere into the lungs. It prevents breathing, and may be partial or complete. Partial choking allows some — though inadequate — air flow into the lungs. Prolonged or complete choking results in asphyxia, or suffocation, which is potentially fatal.
Obstruction of the airway typically occurs in the pharynx or trachea. Young children are more prone to choking than are older people, in part because they often put small objects in their mouth and do not understand the risk of choking that they pose. Young children may choke on small toys or parts of toys, or on household objects, in addition to food. Foods that are round (hotdogs, carrots, grapes) or can adapt their shape to that of the pharynx (bananas, marshmallows), are especially dangerous, and may cause choking in adults, as well as children.
How can you tell if a loved one is choking? The person cannot speak or cry out, or has great difficulty doing so. Breathing, if possible, is laboured, producing gasping or wheezing. The person may desperately clutch at his or her throat or mouth. If breathing is not soon restored, the person’s face will start to turn blue from lack of oxygen. This will be followed by unconsciousness, brain damage, and possibly death if oxygen deprivation continues beyond a few minutes.
If an infant is choking, turning the baby upside down and slapping him on the back may dislodge the obstructing object. To help an older person who is choking, first encourage the person to cough. Give them a few hard back slaps to help force the lodged object out of the airway. If these steps fail, perform the Heimlich maneuver on the person. See the series of videos below, from ProCPR, which demonstrate several ways to help someone who is choking based on age and consciousness.
https://www.youtube.com/watch?v=XOTbjDGZ7wg&t=46s
Conscious Adult Choking, ProCPR, 2016.
https://www.youtube.com/watch?v=5kmsKNvKAvU
Unconscious Adult Choking, ProCPR, 2011.
https://www.youtube.com/watch?v=ZjmbD7aIaf0
Conscious Child Choking, ProCPR, 2009.
https://www.youtube.com/watch?v=Sba0T2XGIn4
Unconscious Child Choking, ProCPR, 2009.
https://www.youtube.com/watch?v=axqIju9CLKA
Conscious Infant Choking, ProCPR, 2011.
https://www.youtube.com/watch?v=_K7Dwy6b2wQ
Unconscious Infant Choking, ProCPR, 2011.
13.2 Summary
- is the process in which oxygen moves from the outside air into the body, and in which carbon dioxide and other waste gases move from inside the body into the outside air. It involves two subsidiary processes: and . Respiration is carried out mainly by the respiratory system.
- The organs of the respiratory system form a continuous system of passages, called the respiratory tract. It has two major divisions: the and the .
- The upper respiratory tract includes the , , and . All of these organs are involved in conduction, or the movement of air into and out of the body. Incoming air is also cleaned, humidified, and warmed as it passes through the upper respiratory tract. The larynx is called the voice box, because it contains the , which are needed to produce vocal sounds.
- The lower respiratory tract includes the trachea, bronchi and bronchioles, and the lungs. The trachea, bronchi, and bronchioles are involved in conduction. Gas exchange takes place only in the lungs, which are the largest organs of the respiratory tract. Lung tissue consists mainly of tiny air sacs called , which is where gas exchange takes place between air in the alveoli and the blood in capillaries surrounding them.
- The respiratory system protects itself from potentially harmful substances in the air by the . This includes mucus-producing cells, which trap particles and pathogens in incoming air. It also includes tiny hair-like cilia that continually move to sweep the mucus and trapped debris away from the lungs and toward the outside of the body.
- The level of carbon dioxide in the blood is monitored by cells in the brain. If the level becomes too high, it triggers a faster rate of breathing, which lowers the level to the normal range. The opposite occurs if the level becomes too low. The respiratory system exchanges gases with the outside air, but it needs the cardiovascular system to carry the gases to and from cells throughout the body.
13.2 Review Questions
- What is respiration, as carried out by the respiratory system? Name the two subsidiary processes it involves.
- Describe the respiratory tract.
- Identify the organs of the upper respiratory tract. What are their functions?
- List the organs of the lower respiratory tract. Which organs are involved only in conduction?
- Where does gas exchange take place?
- How does the respiratory system protect itself from potentially harmful substances in the air?
- Explain how the rate of breathing is controlled.
- Why does the respiratory system need the cardiovascular system to help it perform its main function of gas exchange?
- Describe two ways in which the body prevents food from entering the lungs.
- What is the relationship between respiration and cellular respiration?
13.2 Explore More
https://www.youtube.com/watch?v=8NUxvJS-_0k
How do lungs work? - Emma Bryce, TED-Ed, 2014.
https://www.youtube.com/watch?time_continue=1&v=6iFPs6JlSzY&feature=emb_logo
Why Do Men Have Deeper Voices? BrainStuff - HowStuffWorks, 2015.
https://www.youtube.com/watch?v=rjibeBSnpJ0
Why does your voice change as you get older? - Shaylin A. Schundler, TED-Ed, 2018.
Attributions
Figure 13.2.1
Exhale by pavel-lozovikov-HYovA7yPPvI [photo] by Pavel Lozovikov on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 13.2.2
Illu_conducting_passages.svg by Lord Akryl, Jmarchn from SEER Training Modules/ National Cancer Institute on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 13.2.3
Larynx by www.medicalgraphics.de is used under a CC BY-ND 4.0 (https://creativecommons.org/licenses/by-nd/4.0/) license.
Figure 13.2.4
Larynx top view by Alan Hoofring (Illustrator) for National Cancer Institute is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 13.2.5
2000px-Lungs_diagram_detailed.svg by Patrick J. Lynch, medical illustrator on Wikimedia Commons is used under a CC BY 2.5 (https://creativecommons.org/licenses/by/2.5) license. (Derivative work of Fruchtwasserembolie.png.)
Figure 13.2.6
Gross_Anatomy_of_the_Lungs by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 13.2.7
Alveoli Structure by CNX OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.
Figure 13.2.8
annotated_diagram_of_an_alveolus.svg by Katherinebutler1331 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 13.2.9
Sneeze by James Gathany at CDC Public Health Imagery Library (PHIL) #11162 on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 22.2 Major respiratory structures [digital image]. In Anatomy and Physiology (Section 22.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-1-organs-and-structures-of-the-respiratory-system [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)].
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 22.13 Gross anatomy of the lungs [digital image]. In Anatomy and Physiology (Section 22.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-2-the-lungs
BrainStuff - HowStuffWorks. (2015, December 1). Why do men have deeper voices? YouTube. https://www.youtube.com/watch?v=6iFPs6JlSzY&feature=youtu.be
Dr. Lotz. (2018, January 25). Larynx model - Respiratory system. YouTube. https://www.youtube.com/watch?v=BsyB88mq5rQ&feature=youtu.be
I-Hsun Wu. (2015, March 31). Mucociliary clearance. YouTube. https://www.youtube.com/watch?v=HMB6flEaZwI&feature=youtu.be
OpenStax. (2016, May 27). Figure 9 Terminal bronchioles are connected by respiratory bronchioles to alveolar ducts and alveolar sacs [digital image]. In OpenStax, Biology (Section 39.1). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:35-R0biq@11/Systems-of-Gas-Exchange
ProCPR. (2009, November 24). Conscious child choking. YouTube. https://www.youtube.com/watch?v=ZjmbD7aIaf0&feature=youtu.be
ProCPR. (2009, November 24).Unconscious child choking. YouTube. https://www.youtube.com/watch?v=Sba0T2XGIn4&feature=youtu.be
ProCPR. (2011, February 1). Conscious infant choking. YouTube. https://www.youtube.com/watch?v=axqIju9CLKA&feature=youtu.be
ProCPR. (2011, February 1). Unconscious adult choking. YouTube. https://www.youtube.com/watch?v=5kmsKNvKAvU&feature=youtu.be
ProCPR. (2011, February 1). Unconscious infant choking. YouTube. https://www.youtube.com/watch?v=_K7Dwy6b2wQ&feature=youtu.be
ProCPR. (2016, April 8). Conscious adult choking. YouTube. https://www.youtube.com/watch?v=XOTbjDGZ7wg&feature=youtu.be
TED-Ed. (2014, November 24). How do lungs work? - Emma Bryce. YouTube. https://www.youtube.com/watch?v=8NUxvJS-_0k&feature=youtu.be
TED-Ed. (2018, August 2). Why does your voice change as you get older? - Shaylin A. Schundler. YouTube. https://www.youtube.com/watch?v=rjibeBSnpJ0&feature=youtu.be
A large cavity found in the torso of mammals between the thoracic cavity, which it is separated from by the thoracic diaphragm, and the pelvic cavity. Organs of the abdominal cavity include the stomach, liver, gallbladder, spleen, pancreas, small intestine, kidneys, large intestine, and adrenal glands.
Created by CK-12 Foundation/Adapted by Christine Miller
Doing the ‘Fly
The swimmer in the Figure 13.3.1 photo is doing the butterfly stroke, a swimming style that requires the swimmer to carefully control his breathing so it is coordinated with his swimming movements. Breathing is the process of moving air into and out of the lungs, which are the organs in which gas exchange takes place between the atmosphere and the body. Breathing is also called , and it is one of two parts of the life-sustaining process of respiration. The other part is gas exchange. Before you can understand how breathing is controlled, you need to know how breathing occurs.
How Breathing Occurs
Breathing is a two-step process that includes drawing air into the lungs, or inhaling, and letting air out of the lungs, or exhaling. Both processes are illustrated in Figure 13.3.2.
Inhaling
Inhaling is an active process that results mainly from contraction of a muscle called the diaphragm, shown in Figure 13.3.2. The is a large, dome-shaped muscle below the lungs that separates the (chest) and cavities. When the diaphragm contracts it moves down causing the thoracic cavity to expand, and the contents of the abdomen to be pushed downward. Other muscles — such as intercostal muscles between the ribs — also contribute to the process of , especially when inhalation is forced, as when taking a deep breath. These muscles help increase thoracic volume by expanding the ribs outward. The increase in thoracic volume creates a decrease in thoracic air pressure. With the chest expanded, there is lower air pressure inside the lungs than outside the body, so outside air flows into the lungs via the respiratory tract according the the pressure gradient (high pressure flows to lower pressure).
Exhaling
Exhaling involves the opposite series of events. The diaphragm relaxes, so it moves upward and decreases the volume of the thorax. Air pressure inside the lungs increases, so it is higher than the air pressure outside the lungs. , unlike inhalation, is typically a passive process that occurs mainly due to the elasticity of the lungs. With the change in air pressure, the lungs contract to their pre-inflated size, forcing out the air they contain in the process. Air flows out of the lungs, similar to the way air rushes out of a balloon when it is released. If exhalation is forced, internal intercostal and abdominal muscles may help move the air out of the lungs.
Control of Breathing
Breathing is one of the few vital bodily functions that can be controlled consciously, as well as unconsciously. Think about using your breath to blow up a balloon. You take a long, deep breath, and then you exhale the air as forcibly as you can into the balloon. Both the inhalation and exhalation are consciously controlled.
Conscious Control of Breathing
You can control your breathing by holding your breath, slowing your breathing, or , which is breathing more quickly and shallowly than necessary. You can also exhale or inhale more forcefully or deeply than usual. Conscious control of breathing is common in many activities besides blowing up balloons, including swimming, speech training, singing, playing many different musical instruments (Figure 13.3.3), and doing yoga, to name just a few.
There are limits on the conscious control of breathing. For example, it is not possible for a healthy person to voluntarily stop breathing indefinitely. Before long, there is an irrepressible urge to breathe. If you were able to stop breathing for a long enough time, you would lose consciousness. The same thing would happen if you were to hyperventilate for too long. Once you lose consciousness so you can no longer exert conscious control over your breathing, control of breathing takes over.
Unconscious Control of Breathing
Unconscious breathing is controlled by in the and of the brainstem (see Figure 13.3.4). The respiratory centers automatically and continuously regulate the rate of breathing based on the body’s needs. These are determined mainly by blood acidity, or . When you exercise, for example, carbon dioxide levels increase in the blood, because of increased cellular respiration by muscle cells. The carbon dioxide reacts with water in the blood to produce carbonic acid, making the blood more acidic, so pH falls. The drop in pH is detected by in the medulla. Blood levels of oxygen and carbon dioxide, in addition to pH, are also detected by chemoreceptors in major arteries, which send the “data” to the respiratory centers. The latter respond by sending nerve impulses to the , “telling” it to contract more quickly so the rate of breathing speeds up. With faster breathing, more carbon dioxide is released into the air from the blood, and blood pH returns to the normal range.
The opposite events occur when the level of carbon dioxide in the blood becomes too low and blood pH rises. This may occur with involuntary hyperventilation, which can happen in panic attacks, episodes of severe pain, asthma attacks, and many other situations. When you hyperventilate, you blow off a lot of carbon dioxide, leading to a drop in blood levels of carbon dioxide. The blood becomes more basic (alkaline), causing its pH to rise.
Nasal vs. Mouth Breathing
Nasal breathing is breathing through the nose rather than the mouth, and it is generally considered to be superior to mouth breathing. The hair-lined nasal passages do a better job of filtering particles out of the air before it moves deeper into the respiratory tract. The nasal passages are also better at warming and moistening the air, so nasal breathing is especially advantageous in the winter when the air is cold and dry. In addition, the smaller diameter of the nasal passages creates greater pressure in the lungs during exhalation. This slows the emptying of the lungs, giving them more time to extract oxygen from the air.
Feature: Myth vs. Reality
Drowning is defined as respiratory impairment from being in or under a liquid. It is further classified according to its outcome into: death, ongoing health problems, or no ongoing health problems (full recovery). Four hundred Canadians die annually from drowning, and drowning is one of the leading causes of death in children under the age of five. There are some potentially dangerous myths about drowning, and knowing what they are might save your life or the life of a loved one, especially a child.
Myth | Reality |
---|---|
"People drown when they aspirate water into their lungs." | Generally, in the early stages of drowning, very little water enters the lungs. A small amount of water entering the trachea causes a muscular spasm in the larynx that seals the airway and prevents the passage of water into the lungs. This spasm is likely to last until unconsciousness occurs. |
"You can tell when someone is drowning because they will shout for help and wave their arms to attract attention." | The muscular spasm that seals the airway prevents the passage of air, as well as water, so a person who is drowning is unable to shout or call for help. In addition, instinctive reactions that occur in the final minute or so before a drowning person sinks under the water may look similar to calm, safe behavior. The head is likely to be low in the water, tilted back, with the mouth open. The person may have uncontrolled movements of the arms and legs, but they are unlikely to be visible above the water. |
"It is too late to save a person who is unconscious in the water." | An unconscious person rescued with an airway still sealed from the muscular spasm of the larynx stands a good chance of full recovery if they start receiving CPR within minutes. Without water in the lungs, CPR is much more effective. Even if cardiac arrest has occurred so the heart is no longer beating, there is still a chance of recovery. The longer the brain goes without oxygen, however, the more likely brain cells are to die. Brain death is likely after about six minutes without oxygen, except in exceptional circumstances, such as young people drowning in very cold water. There are examples of children surviving, apparently without lasting ill effects, for as long as an hour in cold water. Rescuers retrieving a child from cold water should attempt resuscitation even after a protracted period of immersion. |
"If someone is drowning, you should start administering CPR immediately, even before you try to get the person out of the water." | Removing a drowning person from the water is the first priority, because CPR is ineffective in the water. The goal should be to bring the person to stable ground as quickly as possible and then to start CPR. |
"You are unlikely to drown unless you are in water over your head." | Depending on circumstances, people have drowned in as little as 30 mm (about 1 ½ in.) of water. Inebriated people or those under the influence of drugs, for example, have been known to have drowned in puddles. Hundreds of children have drowned in the water in toilets, bathtubs, basins, showers, pails, and buckets (see Figure 13.3.5). |
13.3 Summary
- Breathing, or , is the two-step process of drawing air into the lungs (inhaling) and letting air out of the lungs (exhaling). is an active process that results mainly from contraction of a muscle called the diaphragm. is typically a passive process that occurs mainly due to the elasticity of the lungs when the diaphragm relaxes.
- Breathing is one of the few vital bodily functions that can be controlled consciously, as well as unconsciously. Conscious control of breathing is common in many activities, including swimming and singing. There are limits on the conscious control of breathing, however. If you try to hold your breath, for example, you will soon have an irrepressible urge to breathe.
- Unconscious breathing is controlled by respiratory centers in the and of the brainstem. They respond to variations in blood by either increasing or decreasing the rate of breathing as needed to return the pH level to the normal range.
- Nasal breathing is generally considered to be superior to mouth breathing because it does a better job of filtering, warming, and moistening incoming air. It also results in slower emptying of the lungs, which allows more oxygen to be extracted from the air.
- Drowning is a major cause of death in Canada, in particular in children under the age of five. It is important to supervise small children when they are playing in, around, or with water.
13.3 Review Questions
- Define breathing.
- Give examples of activities in which breathing is consciously controlled.
- Explain how unconscious breathing is controlled.
- Young children sometimes threaten to hold their breath until they get something they want. Why is this an idle threat?
- Why is nasal breathing generally considered superior to mouth breathing?
- Give one example of a situation that would cause blood pH to rise excessively. Explain why this occurs.
13.3 Explore More
https://www.youtube.com/watch?v=Kl4cU9sG_08
How breathing works - Nirvair Kaur, TED-Ed, 2012.
https://www.youtube.com/watch?v=yDtKBXOEsoM
How do ventilators work? - Alex Gendler, TED-Ed, 2020.
https://www.youtube.com/watch?v=XFnGhrC_3Gs&feature=emb_logo
How I held my breath for 17 minutes | David Blaine, TED, 2010.
https://www.youtube.com/watch?v=Vca6DyFqt4c&feature=emb_logo
The Ultimate Relaxation Technique: How To Practice Diaphragmatic Breathing For Beginners, Kai Simon, 2015.
Attributions
Figure 13.3.1
US_Marines_butterfly_stroke by Cpl. Jasper Schwartz from U.S. Marine Corps on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 13.3.2
Inhale Exhale/Breathing cycle by Siyavula Education on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/) license.
Figure 13.3.3
Trumpet/ Frenchmen Street [photo] by Morgan Petroski on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 13.3.4
Respiratory_Centers_of_the_Brain by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 13.3.5
Lily & Ava in the Kiddie Pool by mob mob on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure 22.20 Respiratory centers of the brain [digital image]. In Anatomy and Physiology (Section 22.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-3-the-process-of-breathing
Kai Simon. (2015, January 11). The ultimate relaxation technique: How to practice diaphragmatic breathing for beginners. YouTube. https://www.youtube.com/watch?v=Vca6DyFqt4c&feature=youtu.be
TED. (2010, January 19). How I held my breath for 17 minutes | David Blaine. YouTube. https://www.youtube.com/watch?v=XFnGhrC_3Gs&feature=youtu.be
TED-Ed. (2012, October 4). How breathing works - Nirvair Kaur. YouTube. https://www.youtube.com/watch?v=Kl4cU9sG_08&feature=youtu.be
TED-Ed. (2020, May 21). How do ventilators work? - Alex Gendler. YouTube. https://www.youtube.com/watch?v=yDtKBXOEsoM&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
As you learned in this chapter, the human body consists of many complex systems that normally work together efficiently — like a well-oiled machine — to carry out life’s functions. For example, the image above (Figure 7.9.1) illustrates how the brain and spinal cord are protected by layers of membrane called meninges and fluid that flows between the meninges and in spaces called ventricles inside the brain. This fluid is called , and as you have learned, one of its important functions is to cushion and protect the brain and spinal cord, which make up most of the (CNS). Additionally, cerebrospinal fluid circulates nutrients and removes waste products from the CNS. Cerebrospinal fluid is produced continually in the ventricles, circulates throughout the CNS, and is then reabsorbed by the bloodstream. If too much cerebrospinal fluid is produced, its flow is blocked, or not enough is reabsorbed, the system becomes out of balance and it can build up in the ventricles. This causes an enlargement of the ventricles called hydrocephalus that can put pressure on the brain, resulting in the types of neurological problems that former professional football player Jayson, described in the beginning of this chapter, is suffering from.
Recall that Jayson’s symptoms included loss of bladder control, memory loss, and difficulty walking. The cause of his symptoms was not immediately clear, although his doctors suspected that it related to the nervous system, since the nervous system acts as the control centre of the body, controlling and regulating many other organ systems. Jayson’s memory loss directly implicated the brain's involvement, since that is the site of thoughts and memory. The urinary system is also controlled in part by the nervous system, so the inability to hold urine appropriately can also be a sign of a neurological issue. Jayson’s trouble walking involved the muscular system, which works alongside the skeletal system to enable movement of the limbs. In turn, the contraction of muscles is regulated by the nervous system. You can see why a problem in the nervous system can cause a variety of different symptoms by affecting multiple organ systems in the human body.
To try to find the exact cause of Jayson’s symptoms, his doctors performed a lumbar puncture (or spinal tap), which is the removal of some cerebrospinal fluid through a needle inserted into the lower part of the spinal canal. They then analyzed Jayson’s cerebrospinal fluid for the presence of pathogens (such as bacteria) to determine whether an infection was the cause of his neurological symptoms. When no evidence of infection was found, they used an MRI to observe the structures of his brain. This is when they discovered his enlarged ventricles, which are a hallmark of hydrocephalus.
To treat Jayson’s hydrocephalus, a surgeon implanted a device called a shunt in his brain to remove the excess fluid. An illustration of a brain shunt is shown in Figure 9.7.2 . One side of the shunt consists of a small tube, called a catheter, which was inserted into Jayson’s ventricles. Excess cerebrospinal fluid is then drained through a one-way valve to the other end of the shunt, which was threaded under his skin to his abdominal cavity, where the fluid is released and can be reabsorbed by the bloodstream.
Implantation of a shunt is the most common way to treat hydrocephalus, and for some people, it can allow them to recover almost completely. However, there can be complications associated with a brain shunt. The shunt can have mechanical problems or cause an infection. Also, the rate of draining must be carefully monitored and adjusted to balance the rate of cerebrospinal fluid removal with the rate of its production. If it is drained too fast, it is called overdraining, and if it is drained too slowly, it is called underdraining. In the case of underdraining, the pressure on the brain and associated neurological symptoms will persist. In the case of overdraining, the ventricles can collapse, which can cause serious problems, such as the tearing of blood vessels and hemorrhaging. To avoid these problems, some shunts have an adjustable pressure valve, where the rate of draining can be adjusted by placing a special magnet over the scalp. You can see how the proper balance between cerebrospinal fluid production and removal is so critical – both in the causes of hydrocephalus and in its treatment.
In what other ways does your body regulate balance, or maintain a state of homeostasis? In this chapter you learned about the feedback loops that keep body temperature and blood glucose within normal ranges. Other important examples of homeostasis in the human body are the regulation of the pH in the blood and the balance of water in the body. You will learn more about homeostasis in different body systems in the coming chapters.
Thanks to Jayson’s shunt, his symptoms are starting to improve, but he has not fully recovered. Time may tell whether the removal of the excess cerebrospinal fluid from his ventricles will eventually allow him to recover normal functioning or whether permanent damage to his nervous system has already been done. The flow of cerebrospinal fluid might seem simple, but when it gets out of balance, it can easily wreak havoc on multiple organ systems because of the intricate interconnectedness of the systems within the human “machine."
To learn more about hydrocephalus and its treatment, watch this video from Boston Children's Hospital:
https://www.youtube.com/watch?v=bHD8zYImKqA
Hydrocephalus and its treatment | Boston Children’s Hospital, 2011.
Chapter 7 Summary
This chapter provided an overview of the organization and functioning of the human body. You learned that:
- The human body consists of multiple parts that function together to maintain life. The biology of the human body incorporates the body’s structure — or — and the body’s functioning, or .
- The organization of the human body is a hierarchy of increasing size and complexity, starting at the level of and and ending at the level of the entire .
- are the level of organization above atoms and molecules, and they are the basic units of structure and function of the human body. Each cell carries out basic life functions, as well as other specific roles. Cells of the human body show a lot of variation.
-
- Variations in cell function are generally reflected in variations in cell structure.
- Some cells are unattached to other cells and can move freely. Others are attached to each other and cannot move freely. Some cells can divide readily and form new cells, and others can divide only under exceptional circumstances. Many cells are specialized to produce and secrete particular substances.
- All the different cell types within an individual have the same genes. Cells can vary because different genes are expressed depending on the cell type.
- Many common types of human cells consist of several subtypes of cells, each of which has a special structure and function. For example, subtypes of bone cells include , osteoblasts, osteogenic cells, and osteoclasts.
- A is a group of connected cells that have a similar function. There are four basic types of human tissues that make up all the organs of the human body: epithelial, muscle, nervous, and connective tissues.
-
- , such as bone, tendons and blood, are made up of a scattering of living cells that are separated by non-living material, called extracellular matrix.
- , such as skin and mucous membranes, protect the body and its internal organs and secrete or absorb substances.
- are made up of cells that have the unique ability to contract. They include , , and tissues.
- are made up of , which transmit messages, and of various types, which play supporting roles.
- An is a structure that consists of two or more types of tissues that work together to do the same job. The and the are two examples.
-
- Many organs are composed of a major tissue that performs the organ’s main function, as well as other tissues that play supporting roles.
- The human body contains five organs that are considered vital for survival: the heart, brain, , , and . If any of these five organs stops functioning, death of the organism is imminent without medical intervention.
- An is a group of organs that work together to carry out a complex overall function. For example, the provides structure to the body and protects internal organs.
-
- There are 11 major organ systems in the human organism. They are the , , , , , , , , , , and . Only the reproductive system varies significantly between males and females.
- The human body is divided into a number of body cavities. A is a fluid-filled space in the body that holds and protects internal organs. The two largest human body cavities are the ventral cavity and dorsal cavity.
-
- The is at the anterior (or front) of the trunk. It is subdivided into the, and the .
- The is at the posterior (or back) of the body, and includes the head and the back of the trunk. It is subdivided into the and .
- Organ systems of the human body must work together to keep the body alive and functioning normally. This requires communication among organ systems. This is controlled by the and . The autonomic nervous system controls involuntary body functions, such as heart rate and digestion. The endocrine system secretes into the blood that travel to body cells and influence their activities.
-
- is a good example of organ system interactions, because it is a basic life process that occurs in all living cells. It is the intracellular process that breaks down with oxygen to produce carbon dioxide and energy. Cellular respiration requires the interaction of the digestive, cardiovascular, and respiratory systems.
- The is a good example of how the nervous and endocrine systems control other organ system responses. It is triggered by a message from the brain to the endocrine system and prepares the body for flight or a fight. Many organ systems are stimulated to respond, including the cardiovascular, respiratory, and digestive systems.
- Playing softball or doing other voluntary physical activities may involve the interaction of nervous, muscular, skeletal, respiratory, and cardiovascular systems.
- is the condition in which a system such as the human body is maintained in a more or less steady state. It is the job of cells, tissues, organs, and organ systems throughout the body to maintain homeostasis.
-
- For any given variable (such as body temperature), there is a particular that is the physiological optimum value. The spread of values around the set point that is considered insignificant is called the .
- Homeostasis is generally maintained by a that includes a , , , and . Negative feedback serves to reduce an excessive response and to keep a variable within the normal range. Negative feedback loops control body temperature and the blood glucose level.
- Sometimes homeostatic mechanisms fail, resulting in . Diabetes is an example of a disease caused by homeostatic imbalance. Aging can bring about a reduction in the efficiency of the body’s control system, making the elderly more susceptible to disease.
- are not common in biological systems. Positive feedback serves to intensify a response until an end point is reached. Positive feedback loops control blood clotting and childbirth.
The severe and broad impact of hydrocephalus on the body’s systems highlights the importance of the nervous system and its role as the master control system of the body. In the next chapter, you will learn much more about the structures and functioning of this fascinating and important system.
Chapter 7 Review
-
- Compare and contrast tissues and organs.
- Which type of tissue lines the inner and outer surfaces of the body?
- What is a vital organ? What happens if a vital organ stops working?
- Name three organ systems that transport or remove wastes from the body.
- Name two types of tissue in the digestive system.
- Describe one way in which the integumentary and cardiovascular systems work together to regulate homeostasis in the human body.
- True or False: Body cavities are filled with air.
- In which organ system is the pituitary gland? Describe how the pituitary gland increases metabolism.
- When the level of thyroid hormone in the body gets too high, it acts on other cells to reduce production of more thyroid hormone. What type of feedback loop does this represent?
- Hypothetical organ A is the control centre in a feedback loop that helps maintain homeostasis. It secretes molecule A1 which reaches organ B, causing organ B to secrete molecule B1. B1 negatively feeds back onto organ A, reducing the production of A1 when the level of B1 gets too high.
- What is the stimulus in this feedback loop?
- If the level of B1 falls significantly below the set point, what do you think happens to the production of A1? Why?
- What is the effector in this feedback loop?
- If organs A and B are part of the endocrine system, what type of molecules do you think A1 and B1 are likely to be?
- What are the two main systems that allow various organ systems to communicate with each other?
- What are two functions of the hypothalamus?
Attributions
Figure 7.9.1
3D Medical Illustration Meninges Details by Scientific Animations on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.9.2
Hydrocephalus with Shunt from CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
©CK-12 Foundation Licensed under • Terms of Use • Attribution
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 1.3 Levels of structural organization of the human body [digital image]. In Anatomy and Physiology (Section 1.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-2-structural-organization-of-the-human-body
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 1.4 Organ systems of the human body [digital image]. In Anatomy and Physiology (Section 1.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-2-structural-organization-of-the-human-body
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 1.15 Dorsal and ventral body cavities [digital image]. In Anatomy and Physiology (Section 1.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-6-anatomical-terminology
Boston Children's Hospital. (2011, ). Hydrocephalus and its treatment | Boston Children’s Hospital. YouTube. https://www.youtube.com/watch?v=bHD8zYImKqA&feature=youtu.be
Brainard, J/ CK-12 Foundation. (2016). Figure 2 An illustration of a brain shunt [digital image]. In CK-12 College Human Biology (Section 9.8) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/9.8/
File:Body cavities lateral view labeled.jpg. (2018, January 4). Wikimedia Commons. https://commons.wikimedia.org/w/index.php?title=File:Body_Cavities_Lateral_view_labeled.jpg&oldid=276851269. (Original image: Figure 1.15 Dorsal and ventral body cavities, from OpenStax, Anatomy and Physiology.)
File:Body cavities lateral view labeled.jpg. (2018, January 4). Wikimedia Commons. https://commons.wikimedia.org/w/index.php?title=File:Body_Cavities_Lateral_view_labeled.jpg&oldid=276851269. (Original image: OpenStax [Version 8.25 from the textbook OpenStax Anatomy and Physiology] adapted for Review questions by Christine Miller].
A Grandma washing her hands at the kitchen sink
Created by Christine Miller
Figure 7.4.1 Construction — It's important to have the right materials for the job.
The Right Material for the Job
Building a house is a big job and one that requires a lot of different materials for specific purposes. As you can see in Figure 7.4.1, many different types of materials are used to build a complete house, but each type of material fulfills certain functions. You wouldn't use insulation to cover your roof, and you wouldn't use lumber to wire your home. Just as a builder chooses the appropriate materials to build each aspect of a home (wires for electrical, lumber for framing, shingles for roofing), your body uses the right cells for each type of role. When many cells work together to perform a specific function, this is termed a .
Tissues
Groups of connected cells form tissues. The cells in a tissue may all be the same type, or they may be of multiple types. In either case, the cells in the tissue work together to carry out a specific function, and they are always specialized to be able to carry out that function better than any other type of tissue. There are four main types of human tissues: connective, epithelial, muscle, and nervous tissues. We use tissues to build organs and organ systems. The 200 types of cells that the body can produce based on our single set of DNA can create all the types of tissue in the body.
Epithelial Tissue
is made up of cells that line inner and outer body surfaces, such as the skin and the inner surface of the digestive tract. Epithelial tissue that lines inner body surfaces and body openings is called mucous membrane. This type of epithelial tissue produces mucus, a slimy substance that coats mucous membranes and traps pathogens, particles, and debris. Epithelial tissue protects the body and its internal organs, secretes substances (such as hormones) in addition to mucus, and absorbs substances (such as nutrients).
The key identifying feature of epithelial tissue is that it contains a free surface and a basement membrane. The free surface is not attached to any other cells and is either open to the outside of the body, or is open to the inside of a hollow organ or body tube. The basement membrane anchors the epithelial tissue to underlying cells.
Epithelial tissue is identified and named by shape and layering. Epithelial cells exist in three main shapes: squamous, cuboidal, and columnar. These specifically shaped cells can, depending on function, be layered several different ways: simple, stratified, pseudostratified, and transitional.
Epithelial tissue forms coverings and linings and is responsible for a range of functions including diffusion, absorption, secretion and protection. The shape of an epithelial cell can maximize its ability to perform a certain function. The thinner an epithelial cell is, the easier it is for substances to move through it to carry out diffusion and/or absorption. The larger an epithelial cell is, the more room it has in its cytoplasm to be able to make products for secretion, and the more protection it can provide for underlying tissues. Their are three main shapes of epithelial cells: squamous (which is shaped like a pancake- flat and oval), cuboidal (cube shaped), and columnar (tall and rectangular).
Figure 7.4.2 The shape of epithelial tissues is important.
Epithelial tissue will also organize into different layerings depending on their function. For example, multiple layers of cells provide excellent protection, but would no longer be efficient for diffusion, whereas a single layer would work very well for diffusion, but no longer be as protective; a special type of layering called transitional is needed for organs that stretch, like your bladder. Your tissues exhibit the layering that makes them most efficient for the function they are supposed to perform. There are four main layerings found in epithelial tissue: simple (one layer of cells), stratified (many layers of cells), pseudostratified (appears stratified, but upon closer inspection is actually simple), and transitional (can stretch, going from many layers to fewer layers).
Figure 7.4.3 The layerings found in epithelial tissues is important.
See Table 7.4.1 for a summary of the different layering types and shapes epithelial cells can form and their related functions and locations.
Table 7.4.1
Summary of Epithelial Tissue Cells
So far, we have identified epithelial tissue based on shape and layering. The representative diagrams we have seen so far are helpful for visualizing the tissue structures, but it is important to look at real examples of these cells. Since cells are too tiny to see with the naked eye, we rely on microscopes to help us study them. is the study of the microscopic anatomy and cells and tissues. See Table 7.4.2 to see some examples of slides of epithelial tissues prepared for the purpose of histology.
Table 7.4.2
Epithelial Tissues and Histological Samples
Epithelial Tissue Type | Tissue Diagram | Histological Sample |
Stratified squamous
(from skin) |
||
Simple cuboidal
(from kidney tubules) |
||
Pseudostratified ciliated columnar
(from trachea) |
Connective Tissue
Bone and blood are examples of connective tissue. is very diverse. In general, it forms a framework and support structure for body tissues and organs. It's made up of living cells separated by non-living material, called , which can be solid or liquid. The extracellular matrix of bone, for example, is a rigid mineral framework. The extracellular matrix of blood is liquid plasma.
The key identifying feature of connective tissue is that is is composed of a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, based on the nature of the matrix. They look very different from one another, which is a reflection of their different functions:
- Fibrous connective tissue: is characterized by a matrix which is flexible and is made of protein fibres including collagen, elastin and possibly reticular fibres. These tissues are found making up tendons, ligaments, and body membranes.
- Supportive connective tissue: is characterized by a solid matrix and is what is used to make bone and cartilage. These tissues are used for support and protection.
- Fluid connective tissue: is characterized by a fluid matrix and includes both blood and lymph.
Fibrous Connective Tissue
Fibrous connective tissue contains cells called . These cells produce fibres of collagen, elastin, or reticular fibre which makes up the matrix of this type of connective tissue. Based on how tightly packed these fibres are and how they are oriented changes the properties, and therefore the function of the fibrous connective tissue.
- Loose fibrous connective tissue: composed of a loose and disorganized weave of collagen and elastin fibres, creating a tissue that is thin and flexible, yet still tough. This tissue, which is also sometimes referred to as "areolar tissue", is found in membranes and surrounding blood vessels and most body organs. As you can see from the diagram in Figure 7.4.4, loose fibrous connective tissue fulfills the definition of connectives tissue since it is a scattering of cells (fibroblasts) in a non-cellular matrix (a mesh of collagen and elastin fibres). There are two types of specialized loose fibrous connective tissue: reticular and adipose. Adipose tissue stores fat and reticular tissue forms the spleen and lymph nodes.
- Dense Fibrous Connective Tissue: composed of a dense mat of parallel collagen fibres and a scattering of fibroblasts, creating a tissue that is very strong. Dense fibrous connective tissue forms tendons and ligaments, which connect bones to muscles and/or bones to neighbouring bones.
Supportive Connective Tissue
Supportive connective tissue exhibits the defining feature of connective tissue in that it is a scattering of cells in a non-cellular matrix; what sets it apart from other connective tissues is its solid matrix. In this tissue group, the matrix is solid- either bone or cartilage. While fibrous connective tissue contained cells called fibroblasts which produced fibres, supportive connective tissue contains cells that either create bone () or cells that create cartilage ().
Cartilage
Chondrocytes produce the cartilage matrix in which they reside. Cartilage is made up of protein fibres and chondrocytes in lacunae. This is tissue is strong yet flexible and is used many places in the body for protection and support. Cartilage is one of the few tissues that is not vascular (doesn't have a direct blood supply) meaning it relies on diffusion to obtain nutrients and gases; this is the cause of slow healing rates in injuries involving cartilage. There are three main types of cartilage:
- Hyaline cartilage: a smooth, strong and flexible tissue. Found at the ends of ribs and long bones, in the nose, and comprising the entire fetal skeleton.
- Fibrocartilage: a very strong tissue containing thick bundles of collagen. Found in joints that need cushioning from high impact (knees, jaw).
- Elastic cartilage: contains elastic fibres in addition to collagen, giving support with the benefit of elasticity. Found in earlobes and the epiglottis.
Bone
Osteocytes produce the bone matrix in which they reside. Since bone is very solid, these cells reside in small spaces called . This bone tissue is composed of collagen fibres embedded in calcium phosphate giving it strength without brittleness. There are two types of bone: compact and spongy.
- Compact bone: has a dense matrix organized into cylindrical units called osteons. Each osteon contains a central canal (sometimes called a Harversian Canal) which allows for space for blood vessels and nerves, as well as concentric rings of bone matrix and osteocytes in lacunae, as per the diagram here. Compact bone is found in long bones and forms a shell around spongy bone.
- Spongy bone: a very porous type of bone which most often contains bone marrow. It is found at the end of long bones, and makes up the majority of the ribs, shoulder blades and flat bones of the cranium.
Fluid Connective Tissue
Fluid connective tissue has a matrix that is fluid; unlike the other two categories of connective tissue, the cells that reside in the matrix do not actually produce the matrix. Fibroblasts make the fibrous matrix, chondrocytes make the cartilaginous matrix, osteocytes make the bony matrix, yet blood cells do not make the fluid matrix of either lymph or plasma. This tissue still fits the definition of connective tissue in that it is still a scattering of cells in a non-cellular matrix.
There are two types of fluid connective tissue:
- Blood: blood contains three types of cells suspended in plasma, and is contained in the cardiovascular system.
- Eryththrocytes, more commonly called red blood cells, are present in high numbers (roughly 5 million cells per mL) and are responsible for delivering oxygen from to the lungs to all the other areas of the body. These cells are relatively small in size with a diameter of around 7 micrometres and live no longer than 120 days.
- Leukocytes, often referred to as white blood cells, are present in lower numbers (approximately 5 thousand cells per mL) are responsible for various immune functions. They are typically larger than erythrocytes, but can live much longer, particularly white blood cells responsible for long term immunity. The number of leukocytes in your blood can go up or down based on whether or not you are fighting an infection.
- Thrombocytes, also known as platelets, are very small cells responsible for blood clotting. Thrombocytes are not actually true cells, they are fragments of a much larger cell called a megakaryocyte.
- Lymph: contains a liquid matrix and white blood cells and is contained in the lymphatic system, which ultimately drains into the cardiovascular system.
Figure 7.4.11 A stained lymphocyte surrounded by red blood cells viewed using a light microscope.
Muscular Tissue
is made up of cells that have the unique ability to contract- which is the defining feature of muscular tissue. There are three major types of muscle tissue, as pictured in Figure 7.4.12 skeletal, smooth, and cardiac muscle tissues.
Skeletal Muscle
Skeletal muscles are voluntary muscles, meaning that you exercise conscious control over them. Skeletal muscles are attached to bones by tendons, a type of connective tissue. When these muscles shorten to pull on the bones to which they are attached, they enable the body to move. When you are exercising, reading a book, or making dinner, you are using skeletal muscles to move your body to carry out these tasks.
Under the microscope, skeletal muscles are striated (or striped) in appearance, because of their internal structure which contains alternating protein fibres of actin and myosin. Skeletal muscle is described as multinucleated, meaning one "cell" has many nuclei. This is because in utero, individual cells destined to become skeletal muscle fused, forming muscle fibres in a process known as myogenesis. You will learn more about skeletal muscle and how it contracts in the Muscular System.
Smooth Muscle
Smooth muscles are nonstriated muscles- they still contain the muscle fibres actin and myosin, but not in the same alternating arrangement seen in skeletal muscle. Smooth muscle is found in the tubes of the body - in the walls of blood vessels and in the reproductive, gastrointestinal, and respiratory tracts. Smooth muscles are not under voluntary control meaning that they operate unconsciously, via the autonomic nervous system. Smooth muscles move substances through a wave of contraction which cascades down the length of a tube, a process termed .
Watch the YouTube video "What is Peristalsis" by Mister Science to see peristalsis in action.
https://www.youtube.com/watch?v=kVjeNZA5pi4
What is Peristalsis, Mister Science, 2018.
Cardiac Muscle
Cardiac muscles work involuntarily, meaning they are regulated by the autonomic nervous system. This is probably a good thing, since you wouldn't want to have to consciously concentrate on keeping your heart beating all the time! Cardiac muscle, which is found only in the heart, is mononucleated and striated (due to alternating bands of myosin and actin). Their contractions cause the heart to pump blood. In order to make sure entire sections of the heart contract in unison, cardiac muscle tissue contains special cell junctions called , which conduct the electrical signals used to "tell" the chambers of the heart when to contract.
Nervous Tissue
is made up of neurons and a group of cells called neuroglia (also known as glial cells). Nervous tissue makes up the central nervous system (mainly the brain and spinal cord) and peripheral nervous system (the network of nerves that runs throughout the rest of the body). The defining feature of nervous tissue is that it is specialized to be able to generate and conduct nerve impulses. This function is carried out by neurons, and the purpose of neuroglia is to support neurons.
A neuron has several parts to its structure:
- Dendrites which collect incoming nerve impulses
- A cell body, or soma, which contains the majority of the neuron's organelles, including the nucleus
- An axon, which carries nerve impulses away from the soma, to the next neuron in the chain
- A myelin sheath, which encases the axon and increases that rate at which nerve impulses can be conducted
- Axon terminals, which maintain physical contact with the dendrites of neighbouring neurons
Neuroglia can be understood as support staff for the neuron. The neurons have such an important job, they need cells to bring them nutrients, take away cell waste, and build their mylein sheath. There are many types of neuroglia, which are categorized based on their function and/or their location in the nervous system. Neuroglia outnumber neurons by as much as 50 to 1, and are much smaller. See the diagram in 7.4.17 to compare the size and number of neurons and neuroglia.
Try out this memory game to test your tissues knowledge:
7.4 Summary
- Tissues are made up of cells working together.
- There are four main types of tissues: epithelial, connective, muscular and nervous.
- Epithelial tissue makes up the linings and coverings of the body and is characterized by having a free surface and a basement membrane. Types of epithelial tissue are distinguished by shape of cell (squamous, cuboidal or columnar) and layering (simple, stratified, pseudostratified and transitional). Different epithelial tissues can carry out diffusion, secretion, absorption, and/or protection depending on their particular cell shape and layering.
- Connective tissue provides structure and support for the body and is characterized as a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, each characterized by a particular type of matrix:
- Fibrous connective tissue contains protein fibres. Both loose and dense fibrous connective tissue belong in this category.
- Supportive connective tissue contains a very solid matrix, and includes both bone and cartilage.
- Fluid connective tissue contains cells in a fluid matrix with the two types of blood and lymph.
- Muscular tissue's defining feature is that it is contractile. There are three types of muscular tissue: skeletal muscle which is found attached to the skeleton for voluntary movement, smooth muscle which moves substances through body tubes, and cardiac muscle which moves blood through the heart.
- Nervous tissue contains specialized cells called neurons which can conduct electrical impulses. Also found in nervous tissue are neuroglia, which support neurons by providing nutrients, removing wastes, and creating myelin sheath.
7.4 Review Questions
- Define the term tissue.
- If a part of the body needed a lining that was both protective, but still able to absorb nutrients, what would be the best type of epithelial tissue to use?
- Where do you find skeletal muscle? Smooth muscle? Cardiac muscle?
- What are some of the functions of neuroglia?
7.4 Explore More
https://www.youtube.com/watch?v=O0ZvbPak4ck
Types of Human Body Tissue, MoomooMath and Science, 2017.
https://www.youtube.com/watch?v=uHbn7wLN_3k
How to 3D print human tissue - Taneka Jones, TED-Ed, 2019.
https://www.youtube.com/watch?v=1Qfmkd6C8u8
How bones make blood - Melody Smith, TED-Ed, 2020.
Attributions
Figure 7.4.1
- Construction man kneeling in front of wall by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Beige wooden frame by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tambour on green by Pierre Châtel-Innocention Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tags: Construction Studs Plumbing Wiring by JWahl on Pixabay is used under the Pixabay License (https://pixabay.com/es/service/license/).
Figure 7.4.2 and Figure 7.4.3
- Simple columnar epithelium tissue by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple cuboidal epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple squamous epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.4
Loose fibrous connective tissue by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.5
Connective Tissue: Loose Aerolar by Berkshire Community College Bioscience Image Library on Flickr is used under a CC0 1.0 Universal public domain dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
Figure 7.4.6
Dense Fibrous Connective Tissue by by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.7
Dense_connective_tissue-400x by J Jana on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.8
Types_of_Cartilage-new by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 7.4.9
Compact_bone_histology_2014 by Athikhun.suw on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.10
Bone_normal_and_degraded_micro_structure by Gtirouflet on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.11
Lymphocyte2 by NicolasGrandjean on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. [No machine-readable author provided. NicolasGrandjean is assumed, based on copyright claims.]
Figure 7.4.12
Skeletal_muscle_横纹肌1 by 乌拉跨氪 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.13
Smooth_Muscle_new by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 7.4.14
Peristalsis by OpenStax on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 7.4.15
400x Cardiac Muscle by Jessy731 on Flickr is used and adapted by Christine Miller under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 7.4.16
Neuron.svg by User:Dhp1080 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.17
400x Nervous Tissue by Jessy731 on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Table 7.4.1
Summary of Epithelial Tissue Cells, by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Table 7.4.2
- Epithelial_Tissues_Stratified_Squamous_Epithelium_(40230842160) by
Berkshire Community College Bioscience Image Library on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license. - Simple cuboidal epithelial tissue histology by Berkshire Community College on Flickr is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
- Pseudostratified_Epithelium by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.8 Summary of epithelial tissue cells [digital image]. In Anatomy and Physiology (Section 4.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-2-epithelial-tissue
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.16 Types of cartilage [digital image]. In Anatomy and Physiology (Section 4.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-3-connective-tissue-supports-and-protects
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 10.23 Smooth muscle [digital micrograph]. In Anatomy and Physiology (Section 10.8). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-8-smooth-muscle (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 22.5 Pseudostratified ciliated columnar epithelium [digital micrograph]. In Anatomy and Physiology (Section 22.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-1-organs-and-structures-of-the-respiratory-system
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 23.5 Peristalsis [diagram]. In Anatomy and Physiology (Section 23.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/23-2-digestive-system-processes-and-regulation
Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/watch?v=kVjeNZA5pi4
MoomooMath and Science. (2017, May 18). Types of human body tissue. YouTube. https://www.youtube.com/watch?v=O0ZvbPak4ck&feature=youtu.be
Open Stax. (2016, May 27). Figure 6 Loose connective tissue [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
Open Stax. (2016, May 27). Figure 7 Fibrous connective tissue from the tendon [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
TED-Ed. (2019, October 17). How to 3D print human tissue - Taneka Jones. YouTube. https://www.youtube.com/watch?v=uHbn7wLN_3k&feature=youtu.be
TED-Ed. (2020, January 27). How bones make blood - Melody Smith. YouTube. https://www.youtube.com/watch?v=1Qfmkd6C8u8&feature=youtu.be
Image shows the size and shape of a healthy brain and the brain of a patient with severe Alzheimer's Disease. The brain of the person with Alzheimer's disease is substantially smaller, and the shape is distorted.
Contain the Brain
You probably recognize the colourful object in this photo (Figure 7.6.1) as a human brain. The brain is arguably the most important organ in the human body. Fortunately for us, the brain has its own special “container,” called the cranial cavity. The cranial cavity enclosing the brain is just one of several cavities in the human body that form “containers” for vital organs.
What Are Body Cavities?
The human body, like that of many other multicellular organisms, is divided into a number of body cavities. A is a fluid-filled space inside the body that holds and protects internal organs. Human body cavities are separated by membranes and other structures. The two largest human body cavities are the ventral cavity and dorsal cavity. These two body cavities are subdivided into smaller body cavities. Both the dorsal and ventral cavities and their subdivisions are shown in the Figure 7.6.2 diagram.
Ventral Cavity
The is at the anterior (or front) of the trunk. Organs contained within this body cavity include the lungs, heart, stomach, intestines, and reproductive organs. The ventral cavity allows for considerable changes in the size and shape of the organs inside as they perform their functions. Organs such as the lungs, stomach, or uterus, for example, can expand or contract without distorting other tissues or disrupting the activities of nearby organs.
The ventral cavity is subdivided into the and .
- The fills the chest and is subdivided into two pleural cavities and the pericardial cavity. The pleural cavities hold the lungs, and the pericardial cavity holds the heart.
- The fills the lower half of the trunk and is subdivided into the abdominal cavity and the pelvic cavity. The abdominal cavity holds digestive organs and the kidneys, and the pelvic cavity holds reproductive organs and organs of excretion.
Dorsal Cavity
The is at the posterior (or back) of the body, including both the head and the back of the trunk. The dorsal cavity is subdivided into the cranial and spinal cavities.
- The fills most of the upper part of the skull and contains the brain.
- The is a very long, narrow cavity inside the vertebral column. It runs the length of the trunk and contains the spinal cord.
The brain and spinal cord are protected by the bones of the skull and the vertebrae of the spine. They are further protected by the , a three-layer membrane that encloses the brain and spinal cord. A thin layer of is maintained between two of the meningeal layers. This clear fluid is produced by the brain, and it provides extra protection and cushioning for the brain and spinal cord.
Feature: My Human Body
The meninges membranes that protect the brain and spinal cord inside their cavities may become inflamed, generally due to a bacterial or viral infection. This condition is called meningitis, and it can lead to serious long-term consequences such as deafness, epilepsy, or cognitive deficits, especially if not treated quickly. Meningitis can also rapidly become life-threatening, so it is classified as a medical emergency.
Learning the symptoms of meningitis may help you or a loved one get prompt medical attention if you ever develop the disease. Common symptoms include fever, headache, and neck stiffness. Other symptoms include confusion or altered consciousness, vomiting, and an inability to tolerate light or loud noises. Young children often exhibit less specific symptoms, such as irritability, drowsiness, or poor feeding.
Meningitis is diagnosed with a lumbar puncture (commonly known as a "spinal tap"), in which a needle is inserted into the spinal canal to collect a sample of . The fluid is analyzed in a medical lab for the presence of pathogens. If meningitis is diagnosed, treatment consists of antibiotics and sometimes antiviral drugs. Corticosteroids may also be administered to reduce inflammation and the risk of complications (such as brain damage). Supportive measures such as IV fluids may also be provided.
Some types of meningitis can be prevented with a vaccine. Ask your health care professional whether you have had the vaccine or should get it. Giving antibiotics to people who have had significant exposure to certain types of meningitis may reduce their risk of developing the disease. If someone you know is diagnosed with meningitis and you are concerned about contracting the disease yourself, see your doctor for advice.
7.6 Summary
- The human body is divided into a number of body cavities, fluid-filled spaces in the body that hold and protect internal organs. The two largest human body cavities are the ventral cavity and dorsal cavity.
- The ventral cavity is at the anterior (or front) of the trunk. It is subdivided into the thoracic cavity and abdominopelvic cavity.
- The dorsal cavity is at the posterior (or back) of the body, and includes the head and the back of the trunk. It is subdivided into the cranial cavity and spinal cavity.
7.6 Review Questions
-
- What is a body cavity?
- Compare and contrast the ventral and dorsal body cavities.
- Identify the subdivisions of the ventral cavity, and the organs each contains.
- Describe the subdivisions of the dorsal cavity and their contents.
- Identify and describe all the tissues that protect the brain and spinal cord.
- What do you think might happen if fluid were to build up excessively in one of the body cavities?
- Explain why a woman’s body can accommodate a full-term fetus during pregnancy without damaging her internal organs.
- Which body cavity does the needle enter in a lumbar puncture?
- What are the names given to the three body cavity divisions where the heart is located?What are the names given to the three body cavity divisions where the kidneys are located?
7.6 Explore More
https://www.youtube.com/watch?v=IaQdv_dBDqM
Why is meningitis so dangerous? - Melvin Sanicas, TED-Ed, 2018.
Attributions
Figure 7.6.1
Brain Lobes by John A Beal, Department of Cellular Biology & Anatomy, Louisiana State University Health Sciences Center Shreveport on Wikimedia Commons is used under a CC BY 2.5 (https://creativecommons.org/licenses/by/2.5/deed.en) license.
Figure 7.6.2
body_cavities-en.svg by Mysid (SVG) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original by US National Cancer Institute [NCI].)
References
Mayo Clinic Staff. (n.d.). Meningitis. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/meningitis/symptoms-causes/syc-20350508
TED-Ed. (2018, November 19). Why is meningitis so dangerous? - Melvin Sanicas. YouTube. https://www.youtube.com/watch?v=IaQdv_dBDqM&feature=youtu.be
Structures containing neuronal cell bodies in the peripheral nervous system.
Created by: CK-12/Adapted by Christine Miller
Assembly Line
We stay alive because millions of different are taking place inside our bodies all the time. Each of our is like the busy auto assembly line pictured in Figure 3.10.1. Raw materials, half-finished products, and waste materials are constantly being used, produced, transported, and excreted. The "workers" on the cellular assembly line are mainly enzymes. These are the that make happen.
What Are Biochemical Reactions?
that take place inside living things are called . The sum of all the biochemical reactions in an organism is called . Metabolism includes both (energy-releasing) chemical reactions and (energy-absorbing) chemical reactions.
Catabolic Reactions
Exothermic reactions in organisms are called . These reactions break down molecules into smaller units and release energy. An example of a catabolic reaction is the breakdown of glucose during cellular respiration, which releases energy that cells need to carry out life processes.
Anabolic Reactions
Endothermic reactions in organisms are called . These reactions build up bigger molecules from smaller ones and absorb . An example of an anabolic reaction is the joining of to form a . Which type of reactions — catabolic or anabolic — do you think occur when your body digests food?
Enzymes
Most of the biochemical reactions that happen inside of living organisms require help. Why is this the case? For one thing, temperatures inside living things are usually too low for biochemical reactions to occur quickly enough to maintain life. The concentrations of reactants may also be too low for them to come together and react. Where do the biochemical reactions get the help they need to proceed? From the enzymes.
An is a that speeds up a . It is a biological . An enzyme generally works by reducing the amount of needed to start the reaction. The graph in Figure 3.10.2 shows the activation energy needed for glucose to combine with oxygen. Less activation energy is needed when the correct is present than when it is not present.
An enzyme speeds up the reaction by lowering the required activation energy. Compare the activation energy needed with and without the enzyme.
How Well Enzymes Work
Enzymes are involved in most biochemical reactions, and they do their jobs extremely well. A typical biochemical reaction that would take several days or even several centuries to happen without an enzyme is likely to occur in just a split second with the proper enzyme! Without enzymes to speed up biochemical reactions, most organisms could not survive.
Enzymes are substrate-specific. The of an enzyme is the specific substance it affects. Each enzyme works only with a particular substrate, which explains why there are so many different enzymes. In addition, for an enzyme to work, it requires specific conditions, such as the right temperature and pH. Some enzymes work best under acidic conditions, for example, while others work best in neutral environments.
Enzyme-Deficiency Disorders
There are hundreds of known inherited metabolic disorders in humans. In most of them, a single enzyme is either not produced by the body at all, or is otherwise produced in a form that doesn't work. The missing or defective enzyme is like an absentee worker on the cell's assembly line. Imagine the auto assembly line from the image at the start of this section. What if the worker who installed the steering wheel was absent? How would this impact the overall functioning of the vehicle? When an enzyme is missing, toxic chemicals build up, or an essential product isn't made. Generally, the normal enzyme is missing because the individual with the disorder inherited two copies of a gene mutation, which may have originated many generations previously.
Any given inherited metabolic disorder is generally quite rare in the general population. However, there are so many different metabolic disorders that a total of one in 1,000 to 2,500 newborns can be expected to have one.
3.10 Summary
- Biochemical reactions are chemical reactions that take place inside of living things. The sum of all of the biochemical reactions in an organism is called metabolism.
- Metabolism includes catabolic reactions, which are energy-releasing (exothermic) reactions, as well as anabolic reactions, which are energy-absorbing (endothermic) reactions.
- Most biochemical reactions need a biological catalyst called an enzyme to speed up the reaction. Enzymes reduce the amount of activation energy needed for the reaction to begin. Most enzymes are proteins that affect just one specific substance, which is called the enzyme's substrate.
- There are many inherited metabolic disorders in humans. Most of them are caused by a single defective or missing enzyme.
3.10 Review Questions
- What are biochemical reactions?
- Define metabolism.
- Compare and contrast catabolic and anabolic reactions.
- Explain the role of enzymes in biochemical reactions.
- What are enzyme-deficiency disorders?
- Explain why the relatively low temperature of living things, along with the low concentration of reactants, would cause biochemical reactions to occur very slowly in the body without enzymes.
- Answer the following questions about what happens after you eat a sandwich.
- Pieces of the sandwich go into your stomach, where there are digestive enzymes that break down the food. Which type of metabolic reaction is this? Explain your answer.
- During the process of digestion, some of the sandwich is broken down into glucose, which is then further broken down to release energy that your cells can use. Is this an exothermic endothermic reaction? Explain your answer.
- The proteins in the cheese, meat, and bread in the sandwich are broken down into their component amino acids. Then your body uses those amino acids to build new proteins. Which kind of metabolic reaction is represented by the building of these new proteins? Explain your answer.
- Explain why your body doesn’t just use one or two enzymes for all of its biochemical reactions.
- A ________ is the specific substance that an enzyme affects in a biochemical reaction.
- An enzyme is a biological _____________ .
- catabolism
- form of activation energy
- catalyst
- reactant
3.10 Explore More
https://www.youtube.com/watch?v=qgVFkRn8f10&feature=youtu.be
Enzymes (Updated), by The Amoeba Sisters, 2016.
https://www.youtube.com/watch?v=8m6RtOpqvtU&feature=youtu.be
What triggers a chemical reaction? - Kareem Jarrah, TED-Ed, 2015.
Figure 3.10.1
Auto Assembly line by Brian Snelson on Wikimedia Commons is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0) license.
Figure 3.10.2
Enzyme_activation_energy by G. Andruk [IMeowbot at the English language Wikipedia], is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license.
References
Amoeba Sisters. (2016, August 28). Enzymes (updated). YouTube. https://www.youtube.com/watch?v=qgVFkRn8f10&feature=youtu.be
TED-Ed. (2015, January 15). What triggers a chemical reaction? - Kareem Jarrah. YouTube. https://www.youtube.com/watch?v=8m6RtOpqvtU&feature=youtu.be
The chemical processes that occur in a living organism to sustain life.
Image shows a microscopic view of dense fibrous connective tissue. The parallel strands of collagen show up as pink horizontal fibers. The fibroblasts sit in between fibers and are stained a dark purple.
A class of biological molecule consisting of linked monomers of amino acids and which are the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes.
The breakdown of larger molecules into smaller ones.
Image shows both a diagram and microscopic view of each of the three types of cartilage: Hyaline cartilage, which contains chondrocytes in paired lacunae and a smooth-looking matrix; Fibrocartilage with looks marbled due to many layers of collagen, and elastic cartilage which irregular, containing both collagen and elastin fibers.
Figure 7.7.1 Everyone on a baseball team has a special job.
Teamwork
Every player on a baseball team has a special job. In the Figure 7.7.1 collage, each player has their part of the infield or outfield covered in case the ball comes their way. Other players on the team cover different parts of the field, or they pitch or catch the ball. Playing baseball clearly requires teamwork. In that regard, the human body is like a baseball team. All of the organ systems of the human body must work together as a team to keep the body alive and well. Teamwork within the body begins with communication.
Communication Among Organ Systems
Communication among is vital if they are to work together as a team. They must be able to respond to each other and change their responses as needed to keep the body in balance. Communication among organ systems is controlled mainly by the and the .
The autonomic nervous system is the part of the that controls involuntary functions. The autonomic nervous system, for example, controls heart rate, blood flow, and digestion. You don’t have to tell your heart to beat faster or to consciously squeeze muscles to push food through the digestive system. You don’t have to even think about these functions at all! The autonomic nervous system orchestrates all the signals needed to control them. It sends messages between parts of the nervous system, as well as between the nervous system and other organ systems via chemical messengers called neurotransmitters.
The endocrine system is the system of that secrete directly into the bloodstream. Once in the , endocrine hormones circulate to cells everywhere in the body. The endocrine system itself is under control of the nervous system via a part of the brain called the . The hypothalamus secretes hormones that travel directly to cells of the , which is located beneath it. The pituitary gland is the master gland of the endocrine system. Most of its hormones either turn on or turn off other. For example, if the pituitary gland secretes thyroid-stimulating hormone, the hormone travels through the circulation to the thyroid gland, which is stimulated to secrete thyroid hormone. Thyroid hormone then travels to cells throughout the body, where it increases their metabolism.
Examples of Organ System Interactions
An increase in cellular metabolism requires more . Cellular respiration is a good example of organ system interactions, because it is a basic life process that occurs in all living .
Cellular Respiration
Cellular respiration is the intracellular process that breaks down glucose with oxygen to produce carbon dioxide and energy in the form of molecules. It is the process by which cells obtain usable energy to power other cellular processes. Which organ systems are involved in cellular respiration? The needed for cellular respiration comes from the via the . The oxygen needed for cellular respiration comes from the also via the cardiovascular system. The carbon dioxide produced in cellular respiration leaves the body by the opposite route. In short, cellular respiration requires — at a minimum — the digestive, cardiovascular, and respiratory systems.
Fight-or-Flight Response
The well-known is a good example of how the and control other organ system responses. The fight-or-flight response begins when the nervous system perceives sudden danger, as shown in the Figure 7.7.2 diagram. The brain sends a message to the endocrine system (via the pituitary gland) for the adrenal glands to secrete the hormones cortisol and adrenaline. These hormones flood the circulation and affect other organ systems throughout the body, including the cardiovascular, urinary, sensory, and digestive systems. Specific responses include increased heart rate, bladder relaxation, tunnel vision, and a shunting of blood away from the digestive system and toward the muscles, brain, and other vital organs needed to fight or flee.
Playing Baseball
The people playing baseball in the opening collage (Figure 7.7.1) are using multiple organ systems in this voluntary activity. Their are focused on observing and preparing to respond to the next play. Their other systems are being controlled by the . The players are using the , , , and . Can you explain how each of these organ systems is involved in playing baseball?
Feature: Reliable Sources
Teamwork among organ systems allows the human organism to work like a finely tuned machine — at least, it does until one of the organ systems fails. When that happens, other organ systems interacting in the same overall process will also be affected. This is especially likely if the affected system plays a controlling role in the process. An example is type 1 diabetes. This disorder occurs when the pancreas does not secrete the endocrine hormone . Insulin normally is secreted in response to an increasing level of in the blood, and it brings the level of glucose back to normal by stimulating body cells to take up insulin from the blood.
Learn more about type 1 diabetes. Use several reliable Internet sources to answer the following questions:
- In type 1 diabetes, what causes the to fail to produce insulin?
- If type 1 diabetes is not controlled, which organ systems are affected by high blood glucose levels? What are some of the specific effects?
- How can blood glucose levels be controlled in patients with type 1 diabetes?
7.7 Summary
- The human body's organ systems must work together to keep the body alive and functioning normally, which requires communication among systems. This communication is controlled by the and . The autonomic nervous system controls involuntary body functions, such as heart rate and digestion. The endocrine system secretes hormones into the blood that travel to body cells and influence their activities.
- is a good example of organ system interactions, because it is a basic life process that happens in all living cells. It is the intracellular process that breaks down glucose with oxygen to produce carbon dioxide and energy. Cellular respiration requires the interaction of the , , and systems.
- The is a good example of how the and systems control other organ system responses. It is triggered by a message from the brain to the endocrine system and prepares the body for flight or a fight. Many organ systems are stimulated to respond, including the cardiovascular, respiratory, and digestive systems.
- Playing baseball — or doing other voluntary physical activities — may involve the interaction of nervous, muscular, skeletal, respiratory, and cardiovascular systems.
7.7 Review Questions
- What is the autonomic nervous system?
- How do the autonomic nervous system and endocrine system communicate with other organ systems so the systems can interact?
- Explain how the brain communicates with the endocrine system.
- What is the role of the pituitary gland in the endocrine system?
- Identify the organ systems that play a role in cellular respiration.
- How does the hormone adrenaline prepare the body to fight or flee? What specific physiological changes does it bring about?
- Explain the role of the muscular system in digesting food.
- Describe how three different organ systems are involved when a player makes a particular play in baseball, such as catching a fly ball.
- What are two types of molecules that the body uses to communicate between organ systems?
- Explain why hormones can have such a wide variety of effects on the body.
7.7 Explore More
https://www.youtube.com/watch?time_continue=19&v=Ujr0UAbyPS4&feature=emb_logo
3D Medical Animation - Peristalsis in Large Intestine/Bowel ||
©Animated Biomedical Productions (ABP), 2013.
https://www.youtube.com/watch?v=FBnBTkcr6No&feature=emb_logo
Adrenaline: Fight or Flight Response, Henk van 't Klooster, 2013.
https://www.youtube.com/watch?v=m2GywoS77qc
Fight or Flight Response, Bozeman Science, 2012.
Attributions
Figure 7.7.1
- Baseball positions by Michael J on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.de) license.
- US Navy 040229-N-8629D-070 photo by US Navy's Photographer's Mate 2nd Class Brett A. Dawson on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
- David Ortiz batter's box by Albert Yau/ SecondPrint Productions on Flickr is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/deed.es) license.
- Fenway-from Legend's Box by Jared Vincent on Wikipedia is used under a CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/deed.en) license.
Figure 7.7.2
The_Fight_or_Flight_Response by Jvnkfood (original), converted to PNG and reduced to 8-bit by Pokéfan95 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
References
Animated Biomedical Productions. (2013, January 30). 3D Medical animation - Peristalsis in large intestine/bowel || ©ABP. YouTube. https://www.youtube.com/watch?v=Ujr0UAbyPS4&feature=youtu.be
Bozeman Science. (2012, January 9). Fight or flight response. YouTube. https://www.youtube.com/watch?v=m2GywoS77qc&feature=youtu.be
Henk van 't Klooster. (2013). Adrenaline: Fight or flight response. YouTube. https://www.youtube.com/watch?v=FBnBTkcr6No&t=4s
Mayo Clinic Staff. (n.d.). Type 1 diabetes. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/type-1-diabetes/symptoms-causes/syc-20353011
Wikipedia contributors. (2020, July 22). Thyroid-stimulating hormone. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Thyroid-stimulating_hormone&oldid=968942540
Image shows a diagram of the major components of the nervous system. The brain, spinal cord, and major nerves are labelled. The main nerves travelling to the arms are the radial, median and ulnar nerves. The major nerves of the abdomen are the intercostal, lumbar and sacral nerves. The major nerves of the legs are the femoral, sciatic, peroneal, saphenous and tibial nerves.
Image shows a labelled diagram of a neuron. The bulk of the cell's volume resides in the cell body, which is surrounded by branched dendrites. A long slender axon leads away from the cell body and ends in many branched synaptic terminals.
Image shows a diagram labelling components of the central nervous system (includes brain and spinal cord) and the peripheral nervous system (includes ganglion and nerve).
Divisions of the nervous system.
The Nervous System is divided into two major parts: The Central Nervous System which consists of the brain and spinal cord and the Peripheral Nervous System which consists of the Autonomic Nervous System and the Somatic Nervous System. The autonomic nervous system is further divided into the Sympathetic, Parasympathetic, and Enteric Nervous Systems.
In the Blink of an Eye
As you drive into a parking lot, a boy on a skateboard suddenly flies in front of your car across your field of vision. You see the boy in the nick of time and react immediately. You slam on the brakes and steer sharply to the right — all in the blink of an eye. You avoid a collision, but just barely. You’re shaken up, but thankful that no one was hurt. How did you respond so quickly? Rapid responses like this are controlled by your nervous system.
Overview of the Nervous System
The , illustrated in the sketch below, is the human organ system that coordinates all of the body’s and actions, by transmitting electrical signals to and from different parts of the body. Specifically, the nervous system extracts information from the internal and external environments, using . Usually, it then sends signals encoding this information to the , which processes the information to determine an appropriate response. Finally, the brain sends signals to muscles, , or glands to bring about the response. In the example above, your eyes detected the boy, the information traveled to your brain, and your brain told your body to act so as to avoid a collision.
Signals of the Nervous System
The signals sent by the nervous system are electrical signals called , and they are transmitted by special nervous system cells called (or nerve cells), like the one in Figure 8.2.3. Long projections (called axons) from neurons carry nerve impulses directly to specific target cells. A cell that receives nerve impulses from a neuron (typically a muscle or a gland) may be excited to perform a function, inhibited from carrying out an action, or otherwise controlled. In this way, the information transmitted by the nervous system is specific to particular cells and is transmitted very rapidly. In fact, the fastest nerve impulses travel at speeds greater than 100 metres per second! Compare this to the chemical messages carried by the hormones that are secreted into the blood by endocrine glands. These hormonal messages are “broadcast” to all the cells of the body, and they can travel only as quickly as the blood flows through the cardiovascular system.
This simple model of a nerve cell shows part of its long axon which carries nerve impulses to other cells. The multiple shorter projections are called dendrites, and they receive nerve impulses from other cells.
Organization of the Nervous System
As you might predict, the human is very complex. It has multiple divisions, beginning with its two main parts, the (CNS) and the (PNS), as shown in the diagram below (Figure 8.2.4). The CNS includes the and , and the PNS consists mainly of , which are bundles of from neurons. The nerves of the PNS connect the CNS to the rest of the body.
The PNS can be further subdivided into two divisions, known as the and s (Figure 8.2.5). These divisions control different types of functions, and they often interact with the CNS to carry out these functions. The somatic nervous system controls activities that are under control, such as turning a steering wheel. The autonomic nervous system controls activities that are , such as digesting a meal. The autonomic nervous system has three main divisions: the (which controls the fight-or-flight response during emergencies), the (which controls the routine “housekeeping” functions of the body at other times), and the (which provides local control of the digestive system).
8.2 Summary
- The is the human organ system that coordinates all of the body’s and actions, by transmitting signals to and from different parts of the body.
- The nervous system has two major divisions, called the (CNS) and the (PNS). The CNS includes the and , and the PNS consists mainly of that connect the CNS with the rest of the body.
- The PNS can be subdivided into two major divisions: the and the .The somatic system controls activities that are under voluntary control. The autonomic system controls activities that are not under voluntary control. The autonomic nervous system is further divided into the (which controls the fight-or-flight response), the (which controls most routine involuntary responses), and the (which provides local control of the digestive system).
- Electrical signals sent by the nervous system are called . They are transmitted by special cells called . Nerve impulses can travel to specific target cells very rapidly.
8.2 Review Questions
- List the general steps through which the nervous system generates an appropriate response to information from the internal and external environments.
- What are neurons?
- Compare and contrast the central and peripheral nervous systems.
- Which major division of the peripheral nervous system allows you to walk to class? Which major division of the peripheral nervous system controls your heart rate?
- Identify the functions of the three main divisions of the autonomic nervous system.
- What is an axon, and what is its function?
- Define nerve impulses.
- Explain generally how the brain and spinal cord can interact with and control the rest of the body.
- How are nerves and neurons related?
- What type of information from the outside environment do you think is detected by sensory receptors in your ears?
8.2 Explore More
https://www.youtube.com/watch?v=qPix_X-9t7E
The Nervous System, Part 1: Crash Course A&P #8, CrashCourse, 2015.
https://www.youtube.com/watch?v=Nsxw5_Iz7mY&feature=emb_logo
Engineering the Human Nervous System: Megan Moynahan at TEDxBrussels,
TEDx Talks, 2013.
Attributions
Figure 8.2.1
Skateboard_1613 by Autoria propia on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain) (Derivative work of this file: SkateboardinDog.jpg)
Figure 8.2.2
Nervous_system_diagram.svg by The Emirr on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 8.2.3
MultipolarNeuron by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 8.2.4
Overview_of_Nervous_System by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 8.2.5
Divisions of the Nervous System by CK-12 Foundation is used under the CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 12.2 Central and peripheral nervous system [digital image]. In Anatomy and Physiology (Section 12.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-1-basic-structure-and-function-of-the-nervous-system
Brainard, J/ CK-12 Foundation. (2016). Figure 5 [digital image]. In CK-12 College Human Biology (Section 10.2) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/10.2/
CrashCourse. (2015, February 23). The nervous system, Part 1: Crash Course A&P #8. YouTube. https://www.youtube.com/watch?v=qPix_X-9t7E&feature=youtu.be
TEDx Talks. (2013, November 3). Engineering the human nervous system: Megan Moynahan at TEDxBrussels. YouTube. https://www.youtube.com/watch?v=Nsxw5_Iz7mY&feature=youtu.be
Created by CK-12 Foundation/ Adapted by Christine Miller
In the Blink of an Eye
As you drive into a parking lot, a boy on a skateboard suddenly flies in front of your car across your field of vision. You see the boy in the nick of time and react immediately. You slam on the brakes and steer sharply to the right — all in the blink of an eye. You avoid a collision, but just barely. You’re shaken up, but thankful that no one was hurt. How did you respond so quickly? Rapid responses like this are controlled by your nervous system.
Overview of the Nervous System
The , illustrated in the sketch below, is the human organ system that coordinates all of the body’s and actions, by transmitting electrical signals to and from different parts of the body. Specifically, the nervous system extracts information from the internal and external environments, using . Usually, it then sends signals encoding this information to the , which processes the information to determine an appropriate response. Finally, the brain sends signals to muscles, , or glands to bring about the response. In the example above, your eyes detected the boy, the information traveled to your brain, and your brain told your body to act so as to avoid a collision.
Signals of the Nervous System
The signals sent by the nervous system are electrical signals called , and they are transmitted by special nervous system cells called (or nerve cells), like the one in Figure 8.2.3. Long projections (called axons) from neurons carry nerve impulses directly to specific target cells. A cell that receives nerve impulses from a neuron (typically a muscle or a gland) may be excited to perform a function, inhibited from carrying out an action, or otherwise controlled. In this way, the information transmitted by the nervous system is specific to particular cells and is transmitted very rapidly. In fact, the fastest nerve impulses travel at speeds greater than 100 metres per second! Compare this to the chemical messages carried by the hormones that are secreted into the blood by endocrine glands. These hormonal messages are “broadcast” to all the cells of the body, and they can travel only as quickly as the blood flows through the cardiovascular system.
This simple model of a nerve cell shows part of its long axon which carries nerve impulses to other cells. The multiple shorter projections are called dendrites, and they receive nerve impulses from other cells.
Organization of the Nervous System
As you might predict, the human is very complex. It has multiple divisions, beginning with its two main parts, the (CNS) and the (PNS), as shown in the diagram below (Figure 8.2.4). The CNS includes the and , and the PNS consists mainly of , which are bundles of from neurons. The nerves of the PNS connect the CNS to the rest of the body.
The PNS can be further subdivided into two divisions, known as the and s (Figure 8.2.5). These divisions control different types of functions, and they often interact with the CNS to carry out these functions. The somatic nervous system controls activities that are under control, such as turning a steering wheel. The autonomic nervous system controls activities that are , such as digesting a meal. The autonomic nervous system has three main divisions: the (which controls the fight-or-flight response during emergencies), the (which controls the routine “housekeeping” functions of the body at other times), and the (which provides local control of the digestive system).
8.2 Summary
- The is the human organ system that coordinates all of the body’s and actions, by transmitting signals to and from different parts of the body.
- The nervous system has two major divisions, called the (CNS) and the (PNS). The CNS includes the and , and the PNS consists mainly of that connect the CNS with the rest of the body.
- The PNS can be subdivided into two major divisions: the and the .The somatic system controls activities that are under voluntary control. The autonomic system controls activities that are not under voluntary control. The autonomic nervous system is further divided into the (which controls the fight-or-flight response), the (which controls most routine involuntary responses), and the (which provides local control of the digestive system).
- Electrical signals sent by the nervous system are called . They are transmitted by special cells called . Nerve impulses can travel to specific target cells very rapidly.
8.2 Review Questions
- List the general steps through which the nervous system generates an appropriate response to information from the internal and external environments.
- What are neurons?
- Compare and contrast the central and peripheral nervous systems.
- Which major division of the peripheral nervous system allows you to walk to class? Which major division of the peripheral nervous system controls your heart rate?
- Identify the functions of the three main divisions of the autonomic nervous system.
- What is an axon, and what is its function?
- Define nerve impulses.
- Explain generally how the brain and spinal cord can interact with and control the rest of the body.
- How are nerves and neurons related?
- What type of information from the outside environment do you think is detected by sensory receptors in your ears?
8.2 Explore More
https://www.youtube.com/watch?v=qPix_X-9t7E
The Nervous System, Part 1: Crash Course A&P #8, CrashCourse, 2015.
https://www.youtube.com/watch?v=Nsxw5_Iz7mY&feature=emb_logo
Engineering the Human Nervous System: Megan Moynahan at TEDxBrussels,
TEDx Talks, 2013.
Attributions
Figure 8.2.1
Skateboard_1613 by Autoria propia on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain) (Derivative work of this file: SkateboardinDog.jpg)
Figure 8.2.2
Nervous_system_diagram.svg by The Emirr on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 8.2.3
MultipolarNeuron by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 8.2.4
Overview_of_Nervous_System by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 8.2.5
Divisions of the Nervous System by CK-12 Foundation is used under the CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 12.2 Central and peripheral nervous system [digital image]. In Anatomy and Physiology (Section 12.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-1-basic-structure-and-function-of-the-nervous-system
Brainard, J/ CK-12 Foundation. (2016). Figure 5 [digital image]. In CK-12 College Human Biology (Section 10.2) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/10.2/
CrashCourse. (2015, February 23). The nervous system, Part 1: Crash Course A&P #8. YouTube. https://www.youtube.com/watch?v=qPix_X-9t7E&feature=youtu.be
TEDx Talks. (2013, November 3). Engineering the human nervous system: Megan Moynahan at TEDxBrussels. YouTube. https://www.youtube.com/watch?v=Nsxw5_Iz7mY&feature=youtu.be
The fluid filtered from blood, called filtrate, passes through the nephron, much of the filtrate and its contents are reabsorbed into the body.
Glucose (also called dextrose) is a simple sugar with the molecular formula C6H12O6. Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy from sunlight.
Amino acids are organic compounds that combine to form proteins.
Image shows a diagram of the different types of neuroglia. In the central nervous system, ependymal cells, oligodendrocytes, astrocytes and microglia are found. In the peripheral nervous system, satellite cells and schwann cells are found.
Life as Art
This colourful picture (Figure 8.3.1) could be an abstract work of modern art. You might imagine it hanging in an art museum or art gallery. In fact, the picture illustrates real life — not artistic creation. It is a micrograph of human . The neon green structures in the picture are . The neuron is one of two basic types of cells in the nervous system. The other type is the cell.
Neurons
— also called nerve cells — are electrically excitable cells that are the main functional units of the . Their function is to transmit , and they are the only type of human cells that can carry out this function.
Neuron Structure
Figure 8.3.2 shows the structure of a typical neuron. Click on each of the main parts to learn about their functions.
Figure 8.3.2 The structure of a typical neuron.
Neurogenesis
Fully differentiated neurons, with all their special structures, cannot divide and form new daughter neurons. Until recently, scientists thought that new neurons could no longer be formed after the brain developed prenatally. In other words, they thought that people were born with all the brain neurons they would ever have, and as neurons died, they would not be replaced. However, new evidence shows that additional neurons can form in the brain, even in adults, from the division of undifferentiated neural stem cells found throughout the brain. The production of new neurons is called . The extent to which it can occur is not known, but it is not likely to be very great in humans.
Neurons in Nervous Tissues
The in the and consists of gray matter and white matter. contains mainly non-myelinated structures, including the cell bodies and dendrites of neurons. It is gray only in cadavers. Living gray matter is actually more pink than gray (see Figure 8.3.3) consists mainly of axons covered with a , which gives them their white colour. White matter also makes up the of the . Nerves consist of long bundles of myelinated that extend to muscles, organs, or glands throughout the body. The axons in each nerve are bundled together like wires in a cable. Axons in nerves may be more than a metre long in an adult. The longest nerve runs from the base of the spine to the toes.
Types of Neurons
There are hundreds of different types of neurons in the human nervous system that exhibit a variety of structures and functions. Nonetheless, many neurons can be classified functionally based on the direction in which they carry nerve impulses.
- carry nerve impulses from in and to the . They change physical stimuli (such as touch, light, and sound) into nerve impulses.
- , like the one in the diagram below (Figure 8.3.4), carry nerve impulses from the central nervous system to muscles and glands. They change nerve signals into the activation of these structures.
- Within the spinal cord or brain, carry nerve impulses back and forth, often between sensory and motor neurons.
Neuroglia
In addition to neurons, nervous tissues also consist of , also called . The root of the word glial comes from a Greek word meaning “glue,” which reflects earlier ideas about the role of neuroglia in nervous tissues. Neuroglia were thought to be little more than “glue” holding together the all-important neurons, but this is no longer the case. They are now known to play many vital roles in the nervous system. There are several different types of neuroglia, each with a different function. You can see six types of neuroglia in Figure 8.3.5.
In general, neuroglia provide support for neurons and help them carry out the basic function of nervous tissues, which is to transmit nerve impulses. For example, s in the central nervous system and s in the peripheral nervous system generate the lipids that make up , which increase the speed of nerve impulses' transmission. Functions of other neuroglia cells include holding neurons in place, supplying neurons with nutrients, regulating the repair of neurons, destroying pathogens, removing dead neurons, and directing axons to their targets. Neuroglia may also play a role in the transmission of nerve impulses, but this is still under study. Unlike mature neurons, mature glial cells retain the ability to divide by undergoing mitosis.
In the human brain, there are generally roughly equal numbers of neurons and neuroglia. If you think intelligence depends on how many neurons you have, think again. Having a relatively high number of neuroglia is actually associated with higher intelligence. When Einstein’s brain was analyzed, researchers discovered a significantly higher-than-normal ratio of neuroglia to neurons in areas of the brain associated with mathematical processing and language. On an evolutionary scale, as well, an increase in the ratio of neuroglia to neurons is associated with greater intelligence in species.
Feature: My Human Body
Would you like your brain to make new neurons that could help you become a better learner? When it comes to learning new things, what college student wouldn’t want a little more brain power? If research about rats applies to humans, then sustained aerobic exercise (such as running) can increase neurogenesis in the adult brain, and specifically in the hippocampus, a brain structure important for learning temporally and/or spatially complex tasks, as well as memory. Although the research is still at the beginning stages, it suggests that exercise may actually lead to a “smarter” brain. Even if the research results are not ultimately confirmed for humans, though, it can’t hurt to get more aerobic exercise. It is certainly beneficial for your body, if not your brain!
8.3 Summary
- are one of two major types of nervous system cells. They are electrically excitable cells that transmit nerve impulses.
- are the other major type of nervous system cells. There are many types of neuroglia and they have many specific functions. In general, neuroglia function to support, protect, and nourish neurons.
- The main parts of a neuron include the , , and . The cell body contains the . Dendrites receive nerve impulses from other cells, and the axon transmits nerve impulses to other cells at axon terminals. A is a complex membrane junction at the end of an axon terminal that transmits signals to another cell.
- Axons are often wrapped in an electrically-insulating , which is produced by neuroglia. Electrical signals occur at gaps in the myelin sheath, called , which speeds the conduction of nerve impulses down the axon.
- , or the formation of new neurons by cell division, may occur in a mature human brain, but only to a limited extent.
- The nervous tissue in the brain and spinal cord consists of (which contains unmyelinated cell bodies and dendrites of neurons) and (which contains mainly myelinated axons of neurons). Nerves of the peripheral nervous system consist of long bundles of myelinated axons that extend throughout the body.
- There are hundreds of types of neurons in the human nervous system, but many can be classified on the basis of the direction in which they carry nerve impulses. carry nerve impulses away from the body and toward the central nervous system, carry them away from the central nervous system and toward the body, and often carry them between sensory and motor neurons.
8.3 Review Questions
- Describe the myelin sheath and nodes of Ranvier. How does their arrangement allow nerve impulses to travel very rapidly along axons?
- Define neurogenesis. What is the potential for neurogenesis in the human brain?
- Relate neurons to different types of nervous tissues.
- Compare and contrast sensory and motor neurons.
- Identify the role of interneurons.
- Identify four specific functions of neuroglia.
- What is the relationship between the proportion of neuroglia to neurons and intelligence?
8.3 Explore More
https://www.youtube.com/watch?time_continue=1&v=zuLOT6GsAxw&feature=emb_logo
Thriving in the Face of Adversity | Stephanie Buxhoeveden | TEDxHerndon, TEDx Talks, 2015.
https://www.youtube.com/watch?v=B_tjKYvEziI
You can grow new brain cells. Here's how | Sandrine Thuret,
TED, 2015.
Attributions
Figure 8.3.1
Nervous Tissue Confocal Microscopy/ Mouse brain, confocal microscopy by ZEISS Microscopy on Flickr is used under a CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/) license.
Figure 8.3.2
Parts of a Neuron by Open Stax on Wikimedia Commons is used and adapted by Christine Miller under the CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 8.3.3
White_and_Gray_Matter by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 8.3.4
Neuromuscular Junction by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 8.3.5
TypesofNeuroglia by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 18). Figure 12.3 Gray matter and white matter [digital image]. In Anatomy and Physiology (Section 12.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-1-basic-structure-and-function-of-the-nervous-system
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 18). Figure 12.8 Parts of a neuron [digital image]. In Anatomy and Physiology (Section 12.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-2-nervous-tissue
Blausen.com staff. (2014). Types of neuroglia cells [digital image]. Medical gallery of Blausen Medical 2014. WikiJournal of Medicine, 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. Wikiversity.org. https://en.wikiversity.org/wiki/WikiJournal_of_Medicine/Medical_gallery_of_Blausen_Medical_2014
Brainard, J/ CK-12 Foundation. (2016). Figure 3 The axon in this diagram is part of a motor neuron. [digital image]. In CK-12 College Human Biology (Section 10.3) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/10.3/
TED. (2015, October 30). You can grow new brain cells. Here's how | Sandrine Thuret. YouTube. https://www.youtube.com/watch?v=B_tjKYvEziI&feature=youtu.be
TEDx Talks. (2015, April 3). Thriving in the face of adversity | Stephanie Buxhoeveden | TEDxHerndon. YouTube. https://www.youtube.com/watch?v=zuLOT6GsAxw&feature=youtu.be
The ability of an organism to maintain constant internal conditions despite external changes.
The process by which DNA is copied.
Figure 7.4.1 Construction — It's important to have the right materials for the job.
The Right Material for the Job
Building a house is a big job and one that requires a lot of different materials for specific purposes. As you can see in Figure 7.4.1, many different types of materials are used to build a complete house, but each type of material fulfills certain functions. You wouldn't use insulation to cover your roof, and you wouldn't use lumber to wire your home. Just as a builder chooses the appropriate materials to build each aspect of a home (wires for electrical, lumber for framing, shingles for roofing), your body uses the right cells for each type of role. When many cells work together to perform a specific function, this is termed a .
Tissues
Groups of connected cells form tissues. The cells in a tissue may all be the same type, or they may be of multiple types. In either case, the cells in the tissue work together to carry out a specific function, and they are always specialized to be able to carry out that function better than any other type of tissue. There are four main types of human tissues: connective, epithelial, muscle, and nervous tissues. We use tissues to build organs and organ systems. The 200 types of cells that the body can produce based on our single set of DNA can create all the types of tissue in the body.
Epithelial Tissue
is made up of cells that line inner and outer body surfaces, such as the skin and the inner surface of the digestive tract. Epithelial tissue that lines inner body surfaces and body openings is called mucous membrane. This type of epithelial tissue produces mucus, a slimy substance that coats mucous membranes and traps pathogens, particles, and debris. Epithelial tissue protects the body and its internal organs, secretes substances (such as hormones) in addition to mucus, and absorbs substances (such as nutrients).
The key identifying feature of epithelial tissue is that it contains a free surface and a basement membrane. The free surface is not attached to any other cells and is either open to the outside of the body, or is open to the inside of a hollow organ or body tube. The basement membrane anchors the epithelial tissue to underlying cells.
Epithelial tissue is identified and named by shape and layering. Epithelial cells exist in three main shapes: squamous, cuboidal, and columnar. These specifically shaped cells can, depending on function, be layered several different ways: simple, stratified, pseudostratified, and transitional.
Epithelial tissue forms coverings and linings and is responsible for a range of functions including diffusion, absorption, secretion and protection. The shape of an epithelial cell can maximize its ability to perform a certain function. The thinner an epithelial cell is, the easier it is for substances to move through it to carry out diffusion and/or absorption. The larger an epithelial cell is, the more room it has in its cytoplasm to be able to make products for secretion, and the more protection it can provide for underlying tissues. Their are three main shapes of epithelial cells: squamous (which is shaped like a pancake- flat and oval), cuboidal (cube shaped), and columnar (tall and rectangular).
Figure 7.4.2 The shape of epithelial tissues is important.
Epithelial tissue will also organize into different layerings depending on their function. For example, multiple layers of cells provide excellent protection, but would no longer be efficient for diffusion, whereas a single layer would work very well for diffusion, but no longer be as protective; a special type of layering called transitional is needed for organs that stretch, like your bladder. Your tissues exhibit the layering that makes them most efficient for the function they are supposed to perform. There are four main layerings found in epithelial tissue: simple (one layer of cells), stratified (many layers of cells), pseudostratified (appears stratified, but upon closer inspection is actually simple), and transitional (can stretch, going from many layers to fewer layers).
Figure 7.4.3 The layerings found in epithelial tissues is important.
See Table 7.4.1 for a summary of the different layering types and shapes epithelial cells can form and their related functions and locations.
Table 7.4.1
Summary of Epithelial Tissue Cells
So far, we have identified epithelial tissue based on shape and layering. The representative diagrams we have seen so far are helpful for visualizing the tissue structures, but it is important to look at real examples of these cells. Since cells are too tiny to see with the naked eye, we rely on microscopes to help us study them. is the study of the microscopic anatomy and cells and tissues. See Table 7.4.2 to see some examples of slides of epithelial tissues prepared for the purpose of histology.
Table 7.4.2
Epithelial Tissues and Histological Samples
Epithelial Tissue Type | Tissue Diagram | Histological Sample |
Stratified squamous
(from skin) |
||
Simple cuboidal
(from kidney tubules) |
||
Pseudostratified ciliated columnar
(from trachea) |
Connective Tissue
Bone and blood are examples of connective tissue. is very diverse. In general, it forms a framework and support structure for body tissues and organs. It's made up of living cells separated by non-living material, called , which can be solid or liquid. The extracellular matrix of bone, for example, is a rigid mineral framework. The extracellular matrix of blood is liquid plasma.
The key identifying feature of connective tissue is that is is composed of a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, based on the nature of the matrix. They look very different from one another, which is a reflection of their different functions:
- Fibrous connective tissue: is characterized by a matrix which is flexible and is made of protein fibres including collagen, elastin and possibly reticular fibres. These tissues are found making up tendons, ligaments, and body membranes.
- Supportive connective tissue: is characterized by a solid matrix and is what is used to make bone and cartilage. These tissues are used for support and protection.
- Fluid connective tissue: is characterized by a fluid matrix and includes both blood and lymph.
Fibrous Connective Tissue
Fibrous connective tissue contains cells called . These cells produce fibres of collagen, elastin, or reticular fibre which makes up the matrix of this type of connective tissue. Based on how tightly packed these fibres are and how they are oriented changes the properties, and therefore the function of the fibrous connective tissue.
- Loose fibrous connective tissue: composed of a loose and disorganized weave of collagen and elastin fibres, creating a tissue that is thin and flexible, yet still tough. This tissue, which is also sometimes referred to as "areolar tissue", is found in membranes and surrounding blood vessels and most body organs. As you can see from the diagram in Figure 7.4.4, loose fibrous connective tissue fulfills the definition of connectives tissue since it is a scattering of cells (fibroblasts) in a non-cellular matrix (a mesh of collagen and elastin fibres). There are two types of specialized loose fibrous connective tissue: reticular and adipose. Adipose tissue stores fat and reticular tissue forms the spleen and lymph nodes.
- Dense Fibrous Connective Tissue: composed of a dense mat of parallel collagen fibres and a scattering of fibroblasts, creating a tissue that is very strong. Dense fibrous connective tissue forms tendons and ligaments, which connect bones to muscles and/or bones to neighbouring bones.
Supportive Connective Tissue
Supportive connective tissue exhibits the defining feature of connective tissue in that it is a scattering of cells in a non-cellular matrix; what sets it apart from other connective tissues is its solid matrix. In this tissue group, the matrix is solid- either bone or cartilage. While fibrous connective tissue contained cells called fibroblasts which produced fibres, supportive connective tissue contains cells that either create bone () or cells that create cartilage ().
Cartilage
Chondrocytes produce the cartilage matrix in which they reside. Cartilage is made up of protein fibres and chondrocytes in lacunae. This is tissue is strong yet flexible and is used many places in the body for protection and support. Cartilage is one of the few tissues that is not vascular (doesn't have a direct blood supply) meaning it relies on diffusion to obtain nutrients and gases; this is the cause of slow healing rates in injuries involving cartilage. There are three main types of cartilage:
- Hyaline cartilage: a smooth, strong and flexible tissue. Found at the ends of ribs and long bones, in the nose, and comprising the entire fetal skeleton.
- Fibrocartilage: a very strong tissue containing thick bundles of collagen. Found in joints that need cushioning from high impact (knees, jaw).
- Elastic cartilage: contains elastic fibres in addition to collagen, giving support with the benefit of elasticity. Found in earlobes and the epiglottis.
Bone
Osteocytes produce the bone matrix in which they reside. Since bone is very solid, these cells reside in small spaces called . This bone tissue is composed of collagen fibres embedded in calcium phosphate giving it strength without brittleness. There are two types of bone: compact and spongy.
- Compact bone: has a dense matrix organized into cylindrical units called osteons. Each osteon contains a central canal (sometimes called a Harversian Canal) which allows for space for blood vessels and nerves, as well as concentric rings of bone matrix and osteocytes in lacunae, as per the diagram here. Compact bone is found in long bones and forms a shell around spongy bone.
- Spongy bone: a very porous type of bone which most often contains bone marrow. It is found at the end of long bones, and makes up the majority of the ribs, shoulder blades and flat bones of the cranium.
Fluid Connective Tissue
Fluid connective tissue has a matrix that is fluid; unlike the other two categories of connective tissue, the cells that reside in the matrix do not actually produce the matrix. Fibroblasts make the fibrous matrix, chondrocytes make the cartilaginous matrix, osteocytes make the bony matrix, yet blood cells do not make the fluid matrix of either lymph or plasma. This tissue still fits the definition of connective tissue in that it is still a scattering of cells in a non-cellular matrix.
There are two types of fluid connective tissue:
- Blood: blood contains three types of cells suspended in plasma, and is contained in the cardiovascular system.
- Eryththrocytes, more commonly called red blood cells, are present in high numbers (roughly 5 million cells per mL) and are responsible for delivering oxygen from to the lungs to all the other areas of the body. These cells are relatively small in size with a diameter of around 7 micrometres and live no longer than 120 days.
- Leukocytes, often referred to as white blood cells, are present in lower numbers (approximately 5 thousand cells per mL) are responsible for various immune functions. They are typically larger than erythrocytes, but can live much longer, particularly white blood cells responsible for long term immunity. The number of leukocytes in your blood can go up or down based on whether or not you are fighting an infection.
- Thrombocytes, also known as platelets, are very small cells responsible for blood clotting. Thrombocytes are not actually true cells, they are fragments of a much larger cell called a megakaryocyte.
- Lymph: contains a liquid matrix and white blood cells and is contained in the lymphatic system, which ultimately drains into the cardiovascular system.
Figure 7.4.11 A stained lymphocyte surrounded by red blood cells viewed using a light microscope.
Muscular Tissue
is made up of cells that have the unique ability to contract- which is the defining feature of muscular tissue. There are three major types of muscle tissue, as pictured in Figure 7.4.12 skeletal, smooth, and cardiac muscle tissues.
Skeletal Muscle
Skeletal muscles are voluntary muscles, meaning that you exercise conscious control over them. Skeletal muscles are attached to bones by tendons, a type of connective tissue. When these muscles shorten to pull on the bones to which they are attached, they enable the body to move. When you are exercising, reading a book, or making dinner, you are using skeletal muscles to move your body to carry out these tasks.
Under the microscope, skeletal muscles are striated (or striped) in appearance, because of their internal structure which contains alternating protein fibres of actin and myosin. Skeletal muscle is described as multinucleated, meaning one "cell" has many nuclei. This is because in utero, individual cells destined to become skeletal muscle fused, forming muscle fibres in a process known as myogenesis. You will learn more about skeletal muscle and how it contracts in the Muscular System.
Smooth Muscle
Smooth muscles are nonstriated muscles- they still contain the muscle fibres actin and myosin, but not in the same alternating arrangement seen in skeletal muscle. Smooth muscle is found in the tubes of the body - in the walls of blood vessels and in the reproductive, gastrointestinal, and respiratory tracts. Smooth muscles are not under voluntary control meaning that they operate unconsciously, via the autonomic nervous system. Smooth muscles move substances through a wave of contraction which cascades down the length of a tube, a process termed .
Watch the YouTube video "What is Peristalsis" by Mister Science to see peristalsis in action.
https://www.youtube.com/watch?v=kVjeNZA5pi4
What is Peristalsis, Mister Science, 2018.
Cardiac Muscle
Cardiac muscles work involuntarily, meaning they are regulated by the autonomic nervous system. This is probably a good thing, since you wouldn't want to have to consciously concentrate on keeping your heart beating all the time! Cardiac muscle, which is found only in the heart, is mononucleated and striated (due to alternating bands of myosin and actin). Their contractions cause the heart to pump blood. In order to make sure entire sections of the heart contract in unison, cardiac muscle tissue contains special cell junctions called , which conduct the electrical signals used to "tell" the chambers of the heart when to contract.
Nervous Tissue
is made up of neurons and a group of cells called neuroglia (also known as glial cells). Nervous tissue makes up the central nervous system (mainly the brain and spinal cord) and peripheral nervous system (the network of nerves that runs throughout the rest of the body). The defining feature of nervous tissue is that it is specialized to be able to generate and conduct nerve impulses. This function is carried out by neurons, and the purpose of neuroglia is to support neurons.
A neuron has several parts to its structure:
- Dendrites which collect incoming nerve impulses
- A cell body, or soma, which contains the majority of the neuron's organelles, including the nucleus
- An axon, which carries nerve impulses away from the soma, to the next neuron in the chain
- A myelin sheath, which encases the axon and increases that rate at which nerve impulses can be conducted
- Axon terminals, which maintain physical contact with the dendrites of neighbouring neurons
Neuroglia can be understood as support staff for the neuron. The neurons have such an important job, they need cells to bring them nutrients, take away cell waste, and build their mylein sheath. There are many types of neuroglia, which are categorized based on their function and/or their location in the nervous system. Neuroglia outnumber neurons by as much as 50 to 1, and are much smaller. See the diagram in 7.4.17 to compare the size and number of neurons and neuroglia.
Try out this memory game to test your tissues knowledge:
7.4 Summary
- Tissues are made up of cells working together.
- There are four main types of tissues: epithelial, connective, muscular and nervous.
- Epithelial tissue makes up the linings and coverings of the body and is characterized by having a free surface and a basement membrane. Types of epithelial tissue are distinguished by shape of cell (squamous, cuboidal or columnar) and layering (simple, stratified, pseudostratified and transitional). Different epithelial tissues can carry out diffusion, secretion, absorption, and/or protection depending on their particular cell shape and layering.
- Connective tissue provides structure and support for the body and is characterized as a scattering of cells in a non-cellular matrix. There are three main categories of connective tissue, each characterized by a particular type of matrix:
- Fibrous connective tissue contains protein fibres. Both loose and dense fibrous connective tissue belong in this category.
- Supportive connective tissue contains a very solid matrix, and includes both bone and cartilage.
- Fluid connective tissue contains cells in a fluid matrix with the two types of blood and lymph.
- Muscular tissue's defining feature is that it is contractile. There are three types of muscular tissue: skeletal muscle which is found attached to the skeleton for voluntary movement, smooth muscle which moves substances through body tubes, and cardiac muscle which moves blood through the heart.
- Nervous tissue contains specialized cells called neurons which can conduct electrical impulses. Also found in nervous tissue are neuroglia, which support neurons by providing nutrients, removing wastes, and creating myelin sheath.
7.4 Review Questions
- Define the term tissue.
- If a part of the body needed a lining that was both protective, but still able to absorb nutrients, what would be the best type of epithelial tissue to use?
- Where do you find skeletal muscle? Smooth muscle? Cardiac muscle?
- What are some of the functions of neuroglia?
7.4 Explore More
https://www.youtube.com/watch?v=O0ZvbPak4ck
Types of Human Body Tissue, MoomooMath and Science, 2017.
https://www.youtube.com/watch?v=uHbn7wLN_3k
How to 3D print human tissue - Taneka Jones, TED-Ed, 2019.
https://www.youtube.com/watch?v=1Qfmkd6C8u8
How bones make blood - Melody Smith, TED-Ed, 2020.
Attributions
Figure 7.4.1
- Construction man kneeling in front of wall by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Beige wooden frame by Charles Deluvio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tambour on green by Pierre Châtel-Innocention Unsplash is used under the Unsplash License (https://unsplash.com/license).
- Tags: Construction Studs Plumbing Wiring by JWahl on Pixabay is used under the Pixabay License (https://pixabay.com/es/service/license/).
Figure 7.4.2 and Figure 7.4.3
- Simple columnar epithelium tissue by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple cuboidal epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
- Simple squamous epithelium by Kamil Danak on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.4
Loose fibrous connective tissue by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.5
Connective Tissue: Loose Aerolar by Berkshire Community College Bioscience Image Library on Flickr is used under a CC0 1.0 Universal public domain dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
Figure 7.4.6
Dense Fibrous Connective Tissue by by CNX OpenStax. Biology. on Wikimedial Commons is used under a CC BY 4.0. (https://creativecommons.org/licenses/by/4.0) license.
Figure 7.4.7
Dense_connective_tissue-400x by J Jana on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.8
Types_of_Cartilage-new by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 7.4.9
Compact_bone_histology_2014 by Athikhun.suw on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.10
Bone_normal_and_degraded_micro_structure by Gtirouflet on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.11
Lymphocyte2 by NicolasGrandjean on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license. [No machine-readable author provided. NicolasGrandjean is assumed, based on copyright claims.]
Figure 7.4.12
Skeletal_muscle_横纹肌1 by 乌拉跨氪 on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en) license.
Figure 7.4.13
Smooth_Muscle_new by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 7.4.14
Peristalsis by OpenStax on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
Figure 7.4.15
400x Cardiac Muscle by Jessy731 on Flickr is used and adapted by Christine Miller under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Figure 7.4.16
Neuron.svg by User:Dhp1080 on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.4.17
400x Nervous Tissue by Jessy731 on Flickr is used under a CC BY-NC 2.0 (https://creativecommons.org/licenses/by-nc/2.0/) license.
Table 7.4.1
Summary of Epithelial Tissue Cells, by OpenStax College on Wikipedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Table 7.4.2
- Epithelial_Tissues_Stratified_Squamous_Epithelium_(40230842160) by
Berkshire Community College Bioscience Image Library on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license. - Simple cuboidal epithelial tissue histology by Berkshire Community College on Flickr is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/) license.
- Pseudostratified_Epithelium by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.8 Summary of epithelial tissue cells [digital image]. In Anatomy and Physiology (Section 4.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-2-epithelial-tissue
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 4.16 Types of cartilage [digital image]. In Anatomy and Physiology (Section 4.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-3-connective-tissue-supports-and-protects
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 10.23 Smooth muscle [digital micrograph]. In Anatomy and Physiology (Section 10.8). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-8-smooth-muscle (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 22.5 Pseudostratified ciliated columnar epithelium [digital micrograph]. In Anatomy and Physiology (Section 22.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/22-1-organs-and-structures-of-the-respiratory-system
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 23.5 Peristalsis [diagram]. In Anatomy and Physiology (Section 23.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/23-2-digestive-system-processes-and-regulation
Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/watch?v=kVjeNZA5pi4
MoomooMath and Science. (2017, May 18). Types of human body tissue. YouTube. https://www.youtube.com/watch?v=O0ZvbPak4ck&feature=youtu.be
Open Stax. (2016, May 27). Figure 6 Loose connective tissue [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
Open Stax. (2016, May 27). Figure 7 Fibrous connective tissue from the tendon [digital image]. In OpenStax Biology (Section 33.2). OpenStax CNX. https://cnx.org/contents/GFy_h8cu@10.53:-LfhWRES@4/Animal-Primary-Tissues
TED-Ed. (2019, October 17). How to 3D print human tissue - Taneka Jones. YouTube. https://www.youtube.com/watch?v=uHbn7wLN_3k&feature=youtu.be
TED-Ed. (2020, January 27). How bones make blood - Melody Smith. YouTube. https://www.youtube.com/watch?v=1Qfmkd6C8u8&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
Life as Art
This colourful picture (Figure 8.3.1) could be an abstract work of modern art. You might imagine it hanging in an art museum or art gallery. In fact, the picture illustrates real life — not artistic creation. It is a micrograph of human . The neon green structures in the picture are . The neuron is one of two basic types of cells in the nervous system. The other type is the cell.
Neurons
— also called nerve cells — are electrically excitable cells that are the main functional units of the . Their function is to transmit , and they are the only type of human cells that can carry out this function.
Neuron Structure
Figure 8.3.2 shows the structure of a typical neuron. Click on each of the main parts to learn about their functions.
Figure 8.3.2 The structure of a typical neuron.
Neurogenesis
Fully differentiated neurons, with all their special structures, cannot divide and form new daughter neurons. Until recently, scientists thought that new neurons could no longer be formed after the brain developed prenatally. In other words, they thought that people were born with all the brain neurons they would ever have, and as neurons died, they would not be replaced. However, new evidence shows that additional neurons can form in the brain, even in adults, from the division of undifferentiated neural stem cells found throughout the brain. The production of new neurons is called . The extent to which it can occur is not known, but it is not likely to be very great in humans.
Neurons in Nervous Tissues
The in the and consists of gray matter and white matter. contains mainly non-myelinated structures, including the cell bodies and dendrites of neurons. It is gray only in cadavers. Living gray matter is actually more pink than gray (see Figure 8.3.3) consists mainly of axons covered with a , which gives them their white colour. White matter also makes up the of the . Nerves consist of long bundles of myelinated that extend to muscles, organs, or glands throughout the body. The axons in each nerve are bundled together like wires in a cable. Axons in nerves may be more than a metre long in an adult. The longest nerve runs from the base of the spine to the toes.
Types of Neurons
There are hundreds of different types of neurons in the human nervous system that exhibit a variety of structures and functions. Nonetheless, many neurons can be classified functionally based on the direction in which they carry nerve impulses.
- carry nerve impulses from in and to the . They change physical stimuli (such as touch, light, and sound) into nerve impulses.
- , like the one in the diagram below (Figure 8.3.4), carry nerve impulses from the central nervous system to muscles and glands. They change nerve signals into the activation of these structures.
- Within the spinal cord or brain, carry nerve impulses back and forth, often between sensory and motor neurons.
Neuroglia
In addition to neurons, nervous tissues also consist of , also called . The root of the word glial comes from a Greek word meaning “glue,” which reflects earlier ideas about the role of neuroglia in nervous tissues. Neuroglia were thought to be little more than “glue” holding together the all-important neurons, but this is no longer the case. They are now known to play many vital roles in the nervous system. There are several different types of neuroglia, each with a different function. You can see six types of neuroglia in Figure 8.3.5.
In general, neuroglia provide support for neurons and help them carry out the basic function of nervous tissues, which is to transmit nerve impulses. For example, s in the central nervous system and s in the peripheral nervous system generate the lipids that make up , which increase the speed of nerve impulses' transmission. Functions of other neuroglia cells include holding neurons in place, supplying neurons with nutrients, regulating the repair of neurons, destroying pathogens, removing dead neurons, and directing axons to their targets. Neuroglia may also play a role in the transmission of nerve impulses, but this is still under study. Unlike mature neurons, mature glial cells retain the ability to divide by undergoing mitosis.
In the human brain, there are generally roughly equal numbers of neurons and neuroglia. If you think intelligence depends on how many neurons you have, think again. Having a relatively high number of neuroglia is actually associated with higher intelligence. When Einstein’s brain was analyzed, researchers discovered a significantly higher-than-normal ratio of neuroglia to neurons in areas of the brain associated with mathematical processing and language. On an evolutionary scale, as well, an increase in the ratio of neuroglia to neurons is associated with greater intelligence in species.
Feature: My Human Body
Would you like your brain to make new neurons that could help you become a better learner? When it comes to learning new things, what college student wouldn’t want a little more brain power? If research about rats applies to humans, then sustained aerobic exercise (such as running) can increase neurogenesis in the adult brain, and specifically in the hippocampus, a brain structure important for learning temporally and/or spatially complex tasks, as well as memory. Although the research is still at the beginning stages, it suggests that exercise may actually lead to a “smarter” brain. Even if the research results are not ultimately confirmed for humans, though, it can’t hurt to get more aerobic exercise. It is certainly beneficial for your body, if not your brain!
8.3 Summary
- are one of two major types of nervous system cells. They are electrically excitable cells that transmit nerve impulses.
- are the other major type of nervous system cells. There are many types of neuroglia and they have many specific functions. In general, neuroglia function to support, protect, and nourish neurons.
- The main parts of a neuron include the , , and . The cell body contains the . Dendrites receive nerve impulses from other cells, and the axon transmits nerve impulses to other cells at axon terminals. A is a complex membrane junction at the end of an axon terminal that transmits signals to another cell.
- Axons are often wrapped in an electrically-insulating , which is produced by neuroglia. Electrical signals occur at gaps in the myelin sheath, called , which speeds the conduction of nerve impulses down the axon.
- , or the formation of new neurons by cell division, may occur in a mature human brain, but only to a limited extent.
- The nervous tissue in the brain and spinal cord consists of (which contains unmyelinated cell bodies and dendrites of neurons) and (which contains mainly myelinated axons of neurons). Nerves of the peripheral nervous system consist of long bundles of myelinated axons that extend throughout the body.
- There are hundreds of types of neurons in the human nervous system, but many can be classified on the basis of the direction in which they carry nerve impulses. carry nerve impulses away from the body and toward the central nervous system, carry them away from the central nervous system and toward the body, and often carry them between sensory and motor neurons.
8.3 Review Questions
- Describe the myelin sheath and nodes of Ranvier. How does their arrangement allow nerve impulses to travel very rapidly along axons?
- Define neurogenesis. What is the potential for neurogenesis in the human brain?
- Relate neurons to different types of nervous tissues.
- Compare and contrast sensory and motor neurons.
- Identify the role of interneurons.
- Identify four specific functions of neuroglia.
- What is the relationship between the proportion of neuroglia to neurons and intelligence?
8.3 Explore More
https://www.youtube.com/watch?time_continue=1&v=zuLOT6GsAxw&feature=emb_logo
Thriving in the Face of Adversity | Stephanie Buxhoeveden | TEDxHerndon, TEDx Talks, 2015.
https://www.youtube.com/watch?v=B_tjKYvEziI
You can grow new brain cells. Here's how | Sandrine Thuret,
TED, 2015.
Attributions
Figure 8.3.1
Nervous Tissue Confocal Microscopy/ Mouse brain, confocal microscopy by ZEISS Microscopy on Flickr is used under a CC BY-NC-ND 2.0 (https://creativecommons.org/licenses/by-nc-nd/2.0/) license.
Figure 8.3.2
Parts of a Neuron by Open Stax on Wikimedia Commons is used and adapted by Christine Miller under the CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 8.3.3
White_and_Gray_Matter by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) license.
Figure 8.3.4
Neuromuscular Junction by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 8.3.5
TypesofNeuroglia by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0/deed.en) license.
References
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 18). Figure 12.3 Gray matter and white matter [digital image]. In Anatomy and Physiology (Section 12.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-1-basic-structure-and-function-of-the-nervous-system
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2016, May 18). Figure 12.8 Parts of a neuron [digital image]. In Anatomy and Physiology (Section 12.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/12-2-nervous-tissue
Blausen.com staff. (2014). Types of neuroglia cells [digital image]. Medical gallery of Blausen Medical 2014. WikiJournal of Medicine, 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. Wikiversity.org. https://en.wikiversity.org/wiki/WikiJournal_of_Medicine/Medical_gallery_of_Blausen_Medical_2014
Brainard, J/ CK-12 Foundation. (2016). Figure 3 The axon in this diagram is part of a motor neuron. [digital image]. In CK-12 College Human Biology (Section 10.3) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/10.3/
TED. (2015, October 30). You can grow new brain cells. Here's how | Sandrine Thuret. YouTube. https://www.youtube.com/watch?v=B_tjKYvEziI&feature=youtu.be
TEDx Talks. (2015, April 3). Thriving in the face of adversity | Stephanie Buxhoeveden | TEDxHerndon. YouTube. https://www.youtube.com/watch?v=zuLOT6GsAxw&feature=youtu.be
also called vasopressin. A hormone made by the hypothalamus in the brain and stored in the posterior pituitary gland. It tells your kidneys how much water to conserve. ADH constantly regulates and balances the amount of water in your blood.
Created by: CK-12/Adapted by Christine Miller
Giving the Gift of Life
Did you ever donate blood? If you did, then you probably know that your blood type is an important factor in blood transfusions. People vary in the type of blood they inherit, and this determines which type(s) of blood they can safely receive in a transfusion. Do you know your blood type?
What Are Blood Types?
is composed of cells suspended in a liquid called plasma. There are three types of cells in blood: red blood cells, which carry oxygen; white blood cells, which fight infections and other threats; and platelets, which are cell fragments that help blood clot. (or blood group) is a genetic characteristic associated with the presence or absence of certain molecules, called antigens, on the surface of red blood cells. These molecules may help maintain the integrity of the cell membrane, act as receptors, or have other biological functions. A blood group system refers to all of the (s), , and possible and that exist for a particular set of blood type antigens. Human blood group systems include the well-known ABO and Rhesus (Rh) systems, as well as at least 33 others that are less well known.
Antigens and Antibodies
— such as those on the red blood cells — are molecules that the immune system identifies as either self (produced by your own body) or non-self (not produced by your own body). Blood group antigens may be proteinsno post, , glycoproteins (proteins attached to chains of sugars), or glycolipids (lipids attached to chains of sugars), depending on the particular blood group system. If antigens are identified as non-self, the immune system responds by forming antibodies that are specific to the non-self antigens. are large, Y-shaped proteins produced by the immune system that recognize and bind to non-self antigens. The analogy of a lock and key is often used to represent how an antibody and antigen fit together, as shown in the illustration below (Figure 6.5.2). When antibodies bind to antigens, it marks them for destruction by other immune system cells. Non-self antigens may enter your body on pathogens (such as bacteria or viruses), on foods, or on red blood cells in a blood transfusion from someone with a different blood type than your own. The last way is virtually impossible nowadays because of effective blood typing and screening protocols.
Genetics of Blood Type
An individual’s depends on which for a blood group system were inherited from their parents. Generally, blood type is controlled by alleles for a single , or for two or more very closely linked genes. Closely linked genes are almost always inherited together, because there is little or no recombination between them. Like other genetic traits, a person’s blood type is generally fixed for life, but there are rare instances in which blood type can change. This could happen, for example, if an individual receives a bone marrow transplant to treat a disease, such as leukemia. If the bone marrow comes from a donor who has a different blood type, the patient’s blood type may eventually convert to the donor’s blood type, because red blood cells are produced in bone marrow.
ABO Blood Group System
The ABO blood group system is the best known human blood group system. in this system are glycoproteins. These antigens are shown in the list below. There are four common blood types for the ABO system:
- Type A, in which only the A antigen is present.
- Type B, in which only the B antigen is present.
- Type AB, in which both the A and B antigens are present.
- Type O, in which neither the A nor the B antigen is present.
Genetics of the ABO System
The ABO blood group system is controlled by a single on chromosome 9. There are three common for the gene, often represented by the letters A , B , and O. With three alleles, there are six possible genotypes for ABO blood group. Alleles A and B, however, are both dominant to allele O and codominant to each other. This results in just four possible phenotypes (blood types) for the ABO system. These genotypes and phenotypes are shown in Table 6.5.1.
Table 6.5.1
ABO Blood Group System: Genotypes and Phenotypes
ABO Blood Group System | |
Genotype | Phenotype (Blood Type, or Group) |
AA | A |
AO | A |
BB | B |
BO | B |
OO | O |
AB | AB |
The diagram below (Figure 6.5.3) shows an example of how ABO blood type is inherited. In this particular example, the father has blood type A (genotype AO) and the mother has blood type B (genotype BO). This mating type can produce children with each of the four possible ABO , although in any given family, not all phenotypes may be present in the children.
Medical Significance of ABO Blood Type
The ABO system is the most important blood group system in blood transfusions. If red blood cells containing a particular ABO antigen are transfused into a person who lacks that antigen, the person’s immune system will recognize the antigen on the red blood cells as non-self. Antibodies specific to that antigen will attack the red blood cells, causing them to agglutinate (or clump) and break apart. If a unit of incompatible blood were to be accidentally transfused into a patient, a severe reaction (called acute hemolytic transfusion reaction) is likely to occur, in which many red blood cells are destroyed. This may result in kidney failure, shock, and even death. Fortunately, such medical accidents virtually never occur today.
These antibodies are often spontaneously produced in the first years of life, after exposure to common microorganisms in the environment that have antigens similar to blood antigens. Specifically, a person with type A blood will produce anti-B antibodies, while a person with type B blood will produce anti-A antibodies. A person with type AB blood does not produce either antibody, while a person with type O blood produces both anti-A and anti-B antibodies. Once the antibodies have been produced, they circulate in the plasma. The relationship between ABO red blood cell antigens and plasma antibodies is shown in Figure 6.5.4.
The antibodies that circulate in the plasma are for different antigens than those on red blood cells, which are recognized as self antigens.
Which blood types are compatible and which are not? Type O blood contains both anti-A and anti-B antibodies, so people with type O blood can only receive type O blood. However, they can donate blood to people of any ABO blood type, which is why individuals with type O blood are called universal donors. Type AB blood contains neither anti-A nor anti-B antibodies, so people with type AB blood can receive blood from people of any ABO blood type. That’s why individuals with type AB blood are called universal recipients. They can donate blood, however, only to people who also have type AB blood. These and other relationships between blood types of donors and recipients are summarized in the simple diagram to the right.
Geographic Distribution of ABO Blood Groups
The frequencies of blood groups for the ABO system vary around the world. You can see how the A and B alleles and the blood group O are distributed geographically on the maps in Figure 6.5.6.
- Worldwide, B is the rarest ABO allele, so type B blood is the least common ABO blood type. Only about 16 per cent of all people have the B allele. Its highest frequency is in Asia. Its lowest frequency is among the indigenous people of Australia and the Americas.
- The A allele is somewhat more common around the world than the B allele, so type A blood is also more common than type B blood. The highest frequencies of the A allele are in Australian Aborigines, the Lapps (Sami) of Northern Scandinavia, and Blackfoot Native Americans in North America. The allele is nearly absent among Native Americans in Central and South America.
- The O allele is the most common ABO allele around the world, and type O blood is the most common ABO blood type. Almost two-thirds of people have at least one copy of the O allele. It is especially common in Native Americans in Central and South America, where it reaches frequencies close to 100 per cent. It also has relatively high frequencies in Australian Aborigines and Western Europeans. Its frequencies are lowest in Eastern Europe and Central Asia.
Figure 6.5.6 Maps of populations that have the A, B and O alleles.
Evolution of the ABO Blood Group System
The geographic distribution of ABO blood type alleles provides indirect evidence for the evolutionary history of these alleles. Evolutionary biologists hypothesize that the allele for blood type A evolved first, followed by the allele for blood type O, and then by the allele for blood type B. This chronology accounts for the percentages of people worldwide with each blood group, and is also consistent with known patterns of early population movements.
The evolutionary forces of and have no doubt played a significant role in the current distribution of ABO blood types worldwide. Geographic variation in ABO blood groups is also likely to be influenced by , because different blood types are thought to vary in their susceptibility to certain diseases. For example:
- People with type O blood may be more susceptible to cholera and plague. They are also more likely to develop gastrointestinal ulcers.
- People with type A blood may be more susceptible to smallpox and more likely to develop certain cancers.
- People with types A, B, and AB blood appear to be less likely to form blood clots that can cause strokes. However, early in our history, the ability of blood to form clots — which appears greater in people with type O blood — may have been a survival advantage.
- Perhaps the greatest natural selective force associated with ABO blood types is malaria. There is considerable evidence to suggest that people with type O blood are somewhat resistant to malaria, giving them a selective advantage where malaria is endemic.
Rhesus Blood Group System
Another well-known blood group system is the Rhesus (Rh) blood group system. The Rhesus system has dozens of different antigens, but only five main antigens (called D, C, c, E, and e). The major Rhesus antigen is the D antigen. People with the D antigen are called Rh positive (Rh+), and people who lack the D antigen are called Rh negative (Rh-). Rhesus antigens are thought to play a role in transporting ions across cell membranes by acting as channel proteins.
The Rhesus blood group system is controlled by two linked genes on chromosome 1. One gene, called RHD, produces a single antigen, antigen D. The other gene, called RHCE, produces the other four relatively common Rhesus antigens (C, c, E, and e), depending on which alleles for this gene are inherited.
Rhesus Blood Group and Transfusions
After the ABO system, the Rhesus system is the second most important blood group system in blood transfusions. The D antigen is the one most likely to provoke an immune response in people who lack the antigen. People who have the D antigen (Rh+) can be safely transfused with either Rh+ or Rh- blood, whereas people who lack the D antigen (Rh-) can be safely transfused only with Rh- blood.
Unlike anti-A and anti-B antibodies to ABO antigens, anti-D antibodies for the Rhesus system are not usually produced by sensitization to environmental substances. People who lack the D antigen (Rh-), however, may produce anti-D antibodies if exposed to Rh+ blood. This may happen accidentally in a blood transfusion, although this is extremely unlikely today. It may also happen during pregnancy with an Rh+ fetus if some of the fetal blood cells pass into the mother’s blood circulation.
Hemolytic Disease of the Newborn
If a woman who is Rh- is carrying an Rh+ fetus, the fetus may be at risk. This is especially likely if the mother has formed anti-D antibodies during a prior pregnancy because of a mixing of maternal and fetal blood during childbirth. Unlike antibodies against ABO antigens, antibodies against the Rhesus D antigen can cross the placenta and enter the blood of the fetus. This may cause hemolytic disease of the newborn (HDN), also called erythroblastosis fetalis, an illness in which fetal red blood cells are destroyed by maternal antibodies, causing . This illness may range from mild to severe. If it is severe, it may cause brain damage and is sometimes fatal for the fetus or newborn. Fortunately, HDN can be prevented by preventing the formation of anti-D antibodies in the Rh- mother. This is achieved by injecting the mother with a medication called Rho(D) immune globulin.
Geographic Distribution of Rhesus Blood Types
The majority of people worldwide are Rh+, but there is regional variation in this blood group system, as there is with the ABO system. The aboriginal inhabitants of the Americas and Australia originally had very close to 100 per cent Rh+ blood. The frequency of the Rh+ blood type is also very high in African populations, at about 97 to 99 per cent. In East Asia, the frequency of Rh+ is slightly lower, at about 93 to 99 per cent. Europeans have the lowest frequency of the Rh+ blood type at about 83 to 85 per cent.
What explains the population variation in Rhesus blood types? Prior to the advent of modern medicine, Rh+ positive children conceived by Rh- women were at risk of fetal or newborn death or impairment from HDN. This was an enigma, because presumably, natural selection would work to remove the rarer phenotype (Rh-) from populations. However, the frequency of this phenotype is relatively high in many populations.
Recent studies have found evidence that natural selection may actually favor heterozygotes for the Rhesus D antigen. The selective agent in this case is thought to be , a parasitic disease caused by the protozoan Toxoplasma gondii, which is very common worldwide. You can see a life cycle diagram of the parasite in Figure 6.5.7. Infection by this parasite often causes no symptoms at all, or it may cause flu-like symptoms for a few days or weeks. Exposure to the parasite has been linked, however, to increased risk of mental disorders (such as schizophrenia), neurological disorders (such as Alzheimer’s), and other neurological problems, including delayed reaction times. One study found that people who tested positive for antibodies to the parasite were more than twice as likely to be involved in traffic accidents.
People who are heterozygous for the D antigen appear less likely to develop the negative neurological and mental effects of Toxoplasma gondii infection. This could help explain why both phenotypes (Rh+ and Rh-) are maintained in most populations. There are also striking geographic differences in the prevalence of toxoplasmosis worldwide, ranging from zero to 95 per cent in different regions. This could explain geographic variation in the D antigen worldwide, because its strength as a selective agent would vary with its prevalence.
Feature: Myth vs. Reality
Myth |
Reality |
"Your nutritional needs can be determined by your ABO blood type. Knowing your blood type allows you to choose the appropriate foods that will help you lose weight, increase your energy, and live a longer, healthier life." | This idea was proposed in 1996 in a New York Times bestseller Eat Right for Your Type, by Peter D’Adamo, a naturopath. Naturopathy is a method of treating disorders that involves the use of herbs, sunlight, fresh air, and other natural substances. Some medical doctors consider naturopathy a pseudoscience. A major scientific review of the blood type diet could find no evidence to support it. In one study, adults eating the diet designed for blood type A showed improved health — but this occurred in everyone, regardless of their blood type. Because the blood type diet is based solely on blood type, it fails to account for other factors that might require dietary adjustments or restrictions. For example, people with diabetes — but different blood types — would follow different diets, and one or both of the diets might conflict with standard diabetes dietary recommendations and be dangerous. |
"ABO blood type is associated with certain personality traits. People with blood type A, for example, are patient and responsible, but may also be stubborn and tense, whereas people with blood type B are energetic and creative, but may also be irresponsible and unforgiving. In selecting a spouse, both your own and your potential mate’s blood type should be taken into account to ensure compatibility of your personalities." | The belief that blood type is correlated with personality is widely held in Japan and other East Asian countries. The idea was originally introduced in the 1920s in a study commissioned by the Japanese government, but it was later shown to have no scientific support. The idea was revived in the 1970s by a Japanese broadcaster, who wrote popular books about it. There is no scientific basis for the idea, and it is generally dismissed as pseudoscience by the scientific community. Nonetheless, it remains popular in East Asian countries, just as astrology is popular in many other countries. |
6.5 Summary
- Blood type (or blood group) is a genetic characteristic associated with the presence or absence of on the surface of red blood cells. A blood group system refers to all of the (s), , and possible and s that exist for a particular set of blood type antigens.
- Antigens are molecules that the immune system identifies as either self or non-self. If antigens are identified as non-self, the immune system responds by forming antibodies that are specific to the non-self antigens, leading to the destruction of cells bearing the antigens.
- The ABO blood group system is a system of red blood cell antigens controlled by a single gene with three common alleles on chromosome 9. There are four possible ABO blood types: A, B, AB, and O. The ABO system is the most important blood group system in blood transfusions. People with type O blood are universal donors, and people with type AB blood are universal recipients.
- The frequencies of ABO blood type alleles and blood groups vary around the world. The allele for the B antigen is least common, and blood type O is the most common. The evolutionary forces of founder effect, genetic drift, and natural selection are responsible for the geographic distribution of ABO alleles and blood types. People with type O blood, for example, may be somewhat resistant to malaria, possibly giving them a selective advantage where malaria is endemic.
- The Rhesus blood group system is a system of red blood cell antigens controlled by two genes with many alleles on chromosome 1. There are five common Rhesus antigens, of which antigen D is most significant. Individuals who have antigen D are called Rh+, and individuals who lack antigen D are called Rh-. Rh- mothers of Rh+ fetuses may produce antibodies against the D antigen in the fetal blood, causing hemolytic disease of the newborn (HDN).
- The majority of people worldwide are Rh+, but there is regional variation in this blood group system. This variation may be explained by natural selection that favors heterozygotes for the D antigen, because this genotype seems to be protected against some of the neurological consequences of the common parasitic infection toxoplasmosis.
6.5 Review Questions
- Define blood type and blood group system.
- Explain the relationship between antigens and antibodies.
- Identify the alleles, genotypes, and phenotypes in the ABO blood group system.
- Discuss the medical significance of the ABO blood group system.
- Compare the relative worldwide frequencies of the three ABO alleles.
- Give examples of how different ABO blood types vary in their susceptibility to diseases.
- Describe the Rhesus blood group system.
- Relate Rhesus blood groups to blood transfusions.
- What causes hemolytic disease of the newborn?
- Describe how toxoplasmosis may explain the persistence of the Rh- blood type in human populations.
- A woman is blood type O and Rh-, and her husband is blood type AB and Rh+. Answer the following questions about this couple and their offspring.
- What are the possible genotypes of their offspring in terms of ABO blood group?
- What are the possible phenotypes of their offspring in terms of ABO blood group?
- Can the woman donate blood to her husband? Explain your answer.
- Can the man donate blood to his wife? Explain your answer.
- Type O blood is characterized by the presence of O antigens — explain why this statement is false.
- Explain why newborn hemolytic disease may be more likely to occur in a second pregnancy than in a first.
6.5 Explore More
https://www.youtube.com/watch?v=xfZhb6lmxjk
Why do blood types matter? - Natalie S. Hodge, TED-Ed, 2015.
https://www.youtube.com/watch?v=qcZKbjYyOfE
How do blood transfusions work? - Bill Schutt, TED-Ed, 2020.
Attributes
Figure 6.5.1
Following the Blood Donation Trail by EJ Hersom/ USA Department of Defense is in the public domain. [Disclaimer: The appearance of U.S. Department of Defense (DoD) visual information does not imply or constitute DoD endorsement.]
Figure 6.5.2
Antibody by Fvasconcellos on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 6.5.3
ABO system codominance.svg, adapted by YassineMrabet (original "Codominant" image from US National Library of Medicine) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 6.5.4
ABO_blood_type.svg by InvictaHOG on Wikimedia Commons is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
Figure 6.5.5
Blood Donor and recipient ABO by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
Figure 6.5.6
- Map of Blood Group A by Muntuwandi at en.wikipedia on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/) license.
- Map of Blood Group B by Muntuwandi at en.wikipedia on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/) license.
- Map of Blood Group O by anthro palomar at en.wikipedia on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/) license.
Figure 6.5.7
Toxoplasma_gondii_Life_cycle_PHIL_3421_lores by Alexander J. da Silva, PhD/Melanie Moser, Centers for Disease Control and Prevention's Public Health Image Library (PHIL#3421) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
Table 6.5.1
ABO Blood Group System: Genotypes and Phenotypes was created by Christine Miller.
References
Dean, L. (2005). Chapter 4 Hemolytic disease of the newborn. In Blood Groups and Red Cell Antigens [Internet]. National Center for Biotechnology Information (US). https://www.ncbi.nlm.nih.gov/books/NBK2266/
Mayo Clinic Staff. (n.d.). Toxoplasmosis [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/toxoplasmosis/symptoms-causes/syc-20356249
MedlinePlus. (2019, January 29). Hemolytic transfusion reaction [online article]. U.S. National Library of Medicine. https://en.wikipedia.org/w/index.php?title=Chromosome_9&oldid=946440619
TED-Ed. (2015, June 29). Why do blood types matter? - Natalie S. Hodge. YouTube. https://www.youtube.com/watch?v=xfZhb6lmxjk&feature=youtu.be
TED-Ed. (2020, February 18). How do blood transfusions work? - Bill Schutt. YouTube. https://www.youtube.com/watch?v=qcZKbjYyOfE&feature=youtu.be
Wikipedia contributors. (2020, May 10). Chromosome 1. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Chromosome_1&oldid=955942444
Wikipedia contributors. (2020, March 20). Chromosome 9. In Wikipedia. https://en.wikipedia.org/w/index.php?title=Chromosome_9&oldid=946440619
The movement of water or other solvent through a plasma membrane from a region of low solute concentration to a region of high solute concentration.
Created by CK-12 Foundation
Contain the Brain
You probably recognize the colourful object in this photo (Figure 7.6.1) as a human brain. The brain is arguably the most important organ in the human body. Fortunately for us, the brain has its own special “container,” called the cranial cavity. The cranial cavity enclosing the brain is just one of several cavities in the human body that form “containers” for vital organs.
What Are Body Cavities?
The human body, like that of many other multicellular organisms, is divided into a number of body cavities. A is a fluid-filled space inside the body that holds and protects internal organs. Human body cavities are separated by membranes and other structures. The two largest human body cavities are the ventral cavity and dorsal cavity. These two body cavities are subdivided into smaller body cavities. Both the dorsal and ventral cavities and their subdivisions are shown in the Figure 7.6.2 diagram.
Ventral Cavity
The is at the anterior (or front) of the trunk. Organs contained within this body cavity include the lungs, heart, stomach, intestines, and reproductive organs. The ventral cavity allows for considerable changes in the size and shape of the organs inside as they perform their functions. Organs such as the lungs, stomach, or uterus, for example, can expand or contract without distorting other tissues or disrupting the activities of nearby organs.
The ventral cavity is subdivided into the and .
- The fills the chest and is subdivided into two pleural cavities and the pericardial cavity. The pleural cavities hold the lungs, and the pericardial cavity holds the heart.
- The fills the lower half of the trunk and is subdivided into the abdominal cavity and the pelvic cavity. The abdominal cavity holds digestive organs and the kidneys, and the pelvic cavity holds reproductive organs and organs of excretion.
Dorsal Cavity
The is at the posterior (or back) of the body, including both the head and the back of the trunk. The dorsal cavity is subdivided into the cranial and spinal cavities.
- The fills most of the upper part of the skull and contains the brain.
- The is a very long, narrow cavity inside the vertebral column. It runs the length of the trunk and contains the spinal cord.
The brain and spinal cord are protected by the bones of the skull and the vertebrae of the spine. They are further protected by the , a three-layer membrane that encloses the brain and spinal cord. A thin layer of is maintained between two of the meningeal layers. This clear fluid is produced by the brain, and it provides extra protection and cushioning for the brain and spinal cord.
Feature: My Human Body
The meninges membranes that protect the brain and spinal cord inside their cavities may become inflamed, generally due to a bacterial or viral infection. This condition is called meningitis, and it can lead to serious long-term consequences such as deafness, epilepsy, or cognitive deficits, especially if not treated quickly. Meningitis can also rapidly become life-threatening, so it is classified as a medical emergency.
Learning the symptoms of meningitis may help you or a loved one get prompt medical attention if you ever develop the disease. Common symptoms include fever, headache, and neck stiffness. Other symptoms include confusion or altered consciousness, vomiting, and an inability to tolerate light or loud noises. Young children often exhibit less specific symptoms, such as irritability, drowsiness, or poor feeding.
Meningitis is diagnosed with a lumbar puncture (commonly known as a "spinal tap"), in which a needle is inserted into the spinal canal to collect a sample of . The fluid is analyzed in a medical lab for the presence of pathogens. If meningitis is diagnosed, treatment consists of antibiotics and sometimes antiviral drugs. Corticosteroids may also be administered to reduce inflammation and the risk of complications (such as brain damage). Supportive measures such as IV fluids may also be provided.
Some types of meningitis can be prevented with a vaccine. Ask your health care professional whether you have had the vaccine or should get it. Giving antibiotics to people who have had significant exposure to certain types of meningitis may reduce their risk of developing the disease. If someone you know is diagnosed with meningitis and you are concerned about contracting the disease yourself, see your doctor for advice.
7.6 Summary
- The human body is divided into a number of body cavities, fluid-filled spaces in the body that hold and protect internal organs. The two largest human body cavities are the ventral cavity and dorsal cavity.
- The ventral cavity is at the anterior (or front) of the trunk. It is subdivided into the thoracic cavity and abdominopelvic cavity.
- The dorsal cavity is at the posterior (or back) of the body, and includes the head and the back of the trunk. It is subdivided into the cranial cavity and spinal cavity.
7.6 Review Questions
-
- What is a body cavity?
- Compare and contrast the ventral and dorsal body cavities.
- Identify the subdivisions of the ventral cavity, and the organs each contains.
- Describe the subdivisions of the dorsal cavity and their contents.
- Identify and describe all the tissues that protect the brain and spinal cord.
- What do you think might happen if fluid were to build up excessively in one of the body cavities?
- Explain why a woman’s body can accommodate a full-term fetus during pregnancy without damaging her internal organs.
- Which body cavity does the needle enter in a lumbar puncture?
- What are the names given to the three body cavity divisions where the heart is located?What are the names given to the three body cavity divisions where the kidneys are located?
7.6 Explore More
https://www.youtube.com/watch?v=IaQdv_dBDqM
Why is meningitis so dangerous? - Melvin Sanicas, TED-Ed, 2018.
Attributions
Figure 7.6.1
Brain Lobes by John A Beal, Department of Cellular Biology & Anatomy, Louisiana State University Health Sciences Center Shreveport on Wikimedia Commons is used under a CC BY 2.5 (https://creativecommons.org/licenses/by/2.5/deed.en) license.
Figure 7.6.2
body_cavities-en.svg by Mysid (SVG) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain). (Original by US National Cancer Institute [NCI].)
References
Mayo Clinic Staff. (n.d.). Meningitis. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/meningitis/symptoms-causes/syc-20350508
TED-Ed. (2018, November 19). Why is meningitis so dangerous? - Melvin Sanicas. YouTube. https://www.youtube.com/watch?v=IaQdv_dBDqM&feature=youtu.be
Image shows a diagram of the negative feedback loops that maintain homeostasis of body temperature. When body temperature falls, blood vessels constrict so that heat is conserved, sweat glands do not secrete fluid, and shivering generates body heat, which warms the body. When body temperature rises, blood vessels dilate, resulting in heat loss to the environment, sweat glands release fluid and as the fluid evaporates, heat is lost from the body.
What Are You Made of?
Your entire body is made of cells and cells are made of molecules.If you look at your hand, what do you see? Of course, you see skin, which consists of . But what are skin cells made of? Like all living cells, they are made of matter. In fact, all things are made of matter. is anything that takes up space and has mass. Matter, in turn, is made up of chemical substances. A is matter that has a definite composition that is consistent throughout. A chemical substance may be either an element or a compound.
Elements and Atoms
An is a pure substance. It cannot be broken down into other types of substances. Each element is made up of just one type of .
Structure of an Atom
An is the smallest particle of an element that still has the properties of that element. Every substance is composed of atoms. Atoms are extremely small, typically about a ten-billionth of a metre in diametre. However, atoms do not have well-defined boundaries, as suggested by the atomic model shown below.
Every is composed of a central area — called the — and one or more subatomic particles called , which move around the nucleus. The nucleus also consists of subatomic particles. It contains one or more s and typically a similar number of . The number of protons in the nucleus determines the type of element an atom represents. An atom of hydrogen, for example, contains just one proton. Atoms of the same element may have different numbers of neutrons in the nucleus. Atoms of the same element with the same number of protons — but different numbers of neutrons — are called .
Protons have a positive electric charge and neutrons have no electric charge. Virtually all of an atom's mass is in the protons and neutrons in the nucleus. Electrons surrounding the nucleus have almost no mass, as well as a negative electric charge. If the number of protons and electrons in an atom are equal, then an atom is electrically neutral, because the positive and negative charges cancel each other out. If an atom has more or fewer electrons than protons, then it has an overall negative or positive charge, respectively, and it is called an .
The negatively-charged electrons of an atom are attracted to the positively-charged protons in the nucleus by a force called , for which opposite charges attract. Electromagnetic force between protons in the nucleus causes these subatomic particles to repel each other, because they have the same charge. However, the protons and neutrons in the nucleus are attracted to each other by a different force, called , which is usually stronger than the electromagnetic force. Nuclear force repels the positively-charged protons from each other.
Periodic Table of the Elements
There are almost 120 known elements. As you can see in the Periodic Table of the Elements shown below, the majority of elements are metals. Examples of metals are iron (Fe) and copper (Cu). Metals are shiny and good conductors of electricity and heat. Nonmetal elements are far fewer in number. They include hydrogen (H) and oxygen (O). They lack the properties of metals.
The periodic table of the elements arranges elements in groups based on their properties. The element most important to life is carbon (C). Find carbon in the table. What type of element is it: metal or nonmetal?
Compounds and Molecules
A is a unique substance that consists of two or more elements combined in fixed proportions. This means that the composition of a compound is always the same. The smallest particle of most compounds in living things is called a .
Consider water as an example. A molecule of water always contains one atom of oxygen and two atoms of hydrogen. The composition of water is expressed by the chemical formula H2O. A model of a water molecule is shown in Figure 3.2.4.
What causes the atoms of a water molecule to “stick” together? The answer is chemical bonds. A is a force that holds together the atoms of molecules. Bonds in molecules involve the sharing of electrons among atoms. New chemical bonds form when substances react with one another. A is a process that changes some chemical substances into others. A chemical reaction is needed to form a compound, and another chemical reaction is needed to separate the substances in that compound.
3.2 Summary
- All consists of chemical substances. A has a definite composition which is consistent throughout. A chemical substance may be either an element or a compound.
- An is a pure substance that cannot be broken down into other types of substances.
- An is the smallest particle of an element that still has the properties of that element. Atoms, in turn, are composed of subatomic particles, including negative , positive , and neutral . The number of protons in an atom determines the element it represents.
- Atoms have equal numbers of electrons and protons, so they have no charge. Ions are atoms that have lost or gained electrons, and as a result have either a positive or negative charge. Atoms with the same number of protons — but different numbers of neutrons — are called .
- There are almost 120 known elements. The majority of elements are metals. A smaller number are nonmetals. The latter include carbon, hydrogen, and oxygen.
- A compound is a substance that consists of two or more elements in a unique composition. The smallest particle of a compound is called a . Chemical bonds hold together the atoms of molecules. Compounds can form only in chemical reactions, and they can break down only in other chemical reactions.
3.2 Review Questions
- What is an element? Give three examples.
- Define compound. Explain how compounds form.
- Compare and contrast atoms and molecules.
- The compound called water can be broken down into its constituent elements by applying an electric current to it. What ratio of elements is produced in this process?
- Relate ions and isotopes to elements and atoms.
- What is the most important element to life?
- Iron oxide is often known as rust — the reddish substance you might find on corroded metal. The chemical formula for this type of iron oxide is Fe2O3. Answer the following questions about iron oxide and briefly explain each answer.
- Is iron oxide an element or a compound?
- Would one particle of iron oxide be considered a molecule or an atom?
- Describe the relative proportion of atoms in iron oxide.
- What causes the Fe and O to stick together in iron oxide?
- Is iron oxide made of metal atoms, metalloid atoms, nonmetal atoms, or a combination of any of these?
- 14C is an isotope of carbon used in the radiocarbon dating of organic material. The most common isotope of carbon is 12C. Do you think 14C and 12C have different numbers of neutrons or protons? Explain your answer.
- Explain why ions have a positive or negative charge.
- Name the three subatomic particles described in this section.
3.2 Explore More
https://www.youtube.com/watch?v=yQP4UJhNn0I&feature=emb_logo
Just how small is an atom? TED-Ed, 2012
Attributions
Figure 3.2.1
Man Sitting, by Gregory Culmer, on Unsplash, is used under the Unsplash license (https://unsplash.com/license).
Figure 3.2.2
Lithium Atom diagram, by AG Caesar, is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en)
Figure 3.2.3
Periodic Table Armtuk3, by Armtuk, is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/) license.
Figure 3.2.4
Water molecule, by Sakurambo, is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
TED-Ed. (2012, April 16). Just how small is an atom. YouTube. https://www.youtube.com/watch?v=yQP4UJhNn0I&feature=youtu.be
Image shows a diagram of a chemical synapse. The axon terminals of the pre-synaptic neuron are resting on the dendrites of the post-synaptic neuron. In the synapse, the axon terminal contains tiny vesicle filled with neurotransmitters which can be released through exocytosis into the synapse and be absorbed by the neighboring neuron's dendrites.
When Lightning Strikes
This amazing cloud-to-surface lightning occurred when a difference in electrical charge built up in a cloud relative to the ground. When the buildup of charge was great enough, a sudden discharge of electricity occurred. A is similar to a lightning strike. Both a nerve impulse and a lightning strike occur because of differences in electrical charge, and both result in an electric current.
Generating Nerve Impulses
A , like a lightning strike, is an electrical phenomenon. A nerve impulse occurs because of a difference in electrical charge across the plasma membrane of a neuron. How does this difference in electrical charge come about? The answer involves , which are electrically-charged or .
Resting Potential
When a is not actively transmitting a nerve impulse, it is in a resting state, ready to transmit a nerve impulse. During the resting state, the maintains a difference in charge across the of the neuron. The sodium-potassium pump is a mechanism of that moves sodium ions (Na+) out of cells and potassium ions (K+) into cells. The sodium-potassium pump moves both ions from areas of lower to higher concentration, using energy in and carrier proteins in the cell membrane. The video below, "Sodium Potassium Pump" by Amoeba Sisters, describes in greater detail how the sodium-potassium pump works. Sodium is the principal ion in the fluid outside of cells, and potassium is the principal ion in the fluid inside of cells. These differences in concentration create an electrical gradient across the cell membrane, called resting potentialno post. Tightly controlling membrane resting potential is critical for the transmission of nerve impulses.
https://www.youtube.com/watch?v=7NY6XdPBhxo
Sodium Potassium Pump, Amoeba Sisters, 2020.
Action Potential
A nerve impulse is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. The reversal of charge is called an . It begins when the neuron receives a chemical signal from another cell or some other type of . If the stimulus is strong enough to reach , an action potential will take place is a cascade along the axon.
This reversal of charges ripples down the axon of the neuron very rapidly as an electric current, which is illustrated in the diagram below (Figure 8.4.2). A nerve impulse is an all-or-nothing response depending on if the stimulus input was strong enough to reach threshold. If a neuron responds at all, it responds completely. A greater stimulation does not produce a stronger impulse.
In neurons with a myelin sheath on their axon, ions flow across the membrane only at the nodes between sections of myelin. As a result, the action potential appears to jump along the axon membrane from node to node, rather than spreading smoothly along the entire membrane. This increases the speed at which the action potential travels.
Transmitting Nerve Impulses
The place where an axon terminal meets another cell is called a . This is where the transmission of a nerve impulse to another cell occurs. The cell that sends the nerve impulse is called the , and the cell that receives the nerve impulse is called the .
Some synapses are purely electrical and make direct electrical connections between neurons. Most synapses, however, are chemical synapses. Transmission of nerve impulses across chemical synapses is more complex.
Chemical Synapses
At a chemical synapse, both the presynaptic and postsynaptic areas of the cells are full of molecular machinery that is involved in the transmission of nerve impulses. As shown in Figure 8.4.3, the presynaptic area contains many tiny spherical vessels called that are packed with chemicals called . When an reaches the axon terminal of the presynaptic cell, it opens channels that allow calcium to enter the terminal. Calcium causes synaptic vesicles to fuse with the membrane, releasing their contents into the narrow space between the presynaptic and postsynaptic membranes. This area is called the . The neurotransmitter molecules travel across the synaptic cleft and bind to receptors, which are proteins embedded in the membrane of the postsynaptic cell.
Neurotransmitters and Receptors
There are more than a hundred known neurotransmitters, and more than one type of neurotransmitter may be released at a given synapse by a presynaptic cell. For example, it is common for a faster-acting neurotransmitter to be released, along with a slower-acting neurotransmitter. Many neurotransmitters also have multiple types of to which they can bind. Receptors, in turn, can be divided into two general groups: chemically gated ion channels and second messenger systems.
- When a chemically gated ion channel is activated, it forms a passage that allows specific types of ions to flow across the cell membrane. Depending on the type of ion, the effect on the target cell may be or .
- When a second messenger system is activated, it starts a cascade of molecular interactions inside the target cell. This may ultimately produce a wide variety of complex effects, such as increasing or decreasing the sensitivity of the cell to stimuli, or even altering gene transcription.
The effect of a neurotransmitter on a postsynaptic cell depends mainly on the type of receptors that it activates, making it possible for a particular neurotransmitter to have different effects on various target cells. A neurotransmitter might excite one set of target cells, inhibit others, and have complex modulatory effects on still others, depending on the type of receptors. However, some neurotransmitters have relatively consistent effects on other cells. Consider the two most widely used neurotransmitters, and (gamma-aminobutyric acid). Glutamate receptors are either excitatory or modulatory in their effects, whereas GABA receptors are all inhibitory in their effects in adults.
Problems with neurotransmitters or their receptors can cause neurological disorders. The disease myasthenia gravis, for example, is caused by from the immune system blocking receptors for the neurotransmitter in postsynaptic muscle cells. This inhibits the effects of acetylcholine on muscle contractions, producing symptoms, such as muscle weakness and excessive fatigue during simple activities. Some mental illnesses (including depression) are caused, at least in part, by imbalances of certain neurotransmitters in the brain. One of the neurotransmitters involved in depression is thought to be , which normally helps regulate mood, among many other functions. Some antidepressant drugs are thought to help alleviate depression in many patients by normalizing the activity of serotonin in the brain.
8.4 Summary
- A is an electrical phenomenon that occurs because of a difference in electrical charge across the plasma membrane of a neuron.
- The maintains an electrical gradient across the plasma membrane of a neuron when it is not actively transmitting a nerve impulse. This gradient is called the resting potentialno post of the neuron.
- An is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. It begins when the neuron receives a chemical signal from another cell or some other type of stimulus. The action potential travels rapidly down the neuron’s axon as an electric current and occurs in three stages: Depolarization, Repolarization and Recovery.
- A nerve impulse is transmitted to another cell at either an electrical or a chemical . At a chemical synapse, chemicals are released from the presynaptic cell into the synaptic cleft between cells. The chemicals travel across the cleft to the postsynaptic cell and bind to receptors embedded in its membrane.
- There are many different types of neurotransmitters. Their effects on the postsynaptic cell generally depend on the type of receptor they bind to. The effects may be excitatory, inhibitory, or modulatory in more complex ways. Both physical and mental disorders may occur if there are problems with neurotransmitters or their receptors.
8.4 Review Questions
- Define nerve impulse.
- What is the resting potential of a neuron, and how is it maintained?
- Explain how and why an action potential occurs.
- Outline how a signal is transmitted from a presynaptic cell to a postsynaptic cell at a chemical synapse.
- What generally determines the effects of a neurotransmitter on a postsynaptic cell?
- Identify three general types of effects that neurotransmitters may have on postsynaptic cells.
- Explain how an electrical signal in a presynaptic neuron causes the transmission of a chemical signal at the synapse.
- The flow of which type of ion into a neuron results in an action potential? How do these ions get into the cell? What does this flow of ions do to the relative charge inside the neuron compared to the outside?
- Name three neurotransmitters.
8.4 Explore More
https://www.youtube.com/watch?v=FEHNIELPb0s
Action Potentials, Teacher's Pet, 2018.
https://www.youtube.com/watch?v=rBcU_apy0h8
TED Ed| What is depression? - Helen M. Farrell, Parta Learning, 2017.
https://youtu.be/ZE8sRMZ5BCA
5 Weird Involuntary Behaviors Explained!, It's Okay To Be Smart, 2015.
Attributions
Figure 8.4.1
Lightening/ Purple Lightning, Dee Why by Jeremy Bishop on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 8.4.2
Action Potential by CNX OpenStax, Biology on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 8.4.3
Chemical_synapse_schema_cropped by Looie496 created file (adapted from original from US National Institutes of Health, National Institute on Aging) is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Amoeba Sisters. (2020, January 29). Sodium potassium pump. YouTube. https://www.youtube.com/watch?v=7NY6XdPBhxo&feature=youtu.be
CNX OpenStax. (2016, May 27) Figure 4 The
It's Okay To Be Smart. (2015, January 26). 5 Weird involuntary behaviors explained! YouTube. https://www.youtube.com/watch?v=ZE8sRMZ5BCA&feature=youtu.be
Mayo Clinic Staff. (n.d.). Depression (major depressive disorder) [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/depression/symptoms-causes/syc-20356007
Mayo Clinic Staff. (n.d.). Myasthenia gravis [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/myasthenia-gravis/symptoms-causes/syc-20352036
National Institute on Aging. (2006, April 8). Alzheimers disease: Unraveling the mystery. National Institutes of Health. https://www.nia.nih.gov/ (archived version)
Parta Learning. (2017, December 8). TED Ed| What is depression? - Helen M. Farrell. YouTube. https://www.youtube.com/watch?v=rBcU_apy0h8&t=291s
Teacher's Pet. (2018, August 26). Action potentials. YouTube. https://www.youtube.com/watch?v=FEHNIELPb0s&feature=youtu.be
Created by CK-12 Foundation/Adapted by Christine Miller
When Lightning Strikes
This amazing cloud-to-surface lightning occurred when a difference in electrical charge built up in a cloud relative to the ground. When the buildup of charge was great enough, a sudden discharge of electricity occurred. A is similar to a lightning strike. Both a nerve impulse and a lightning strike occur because of differences in electrical charge, and both result in an electric current.
Generating Nerve Impulses
A , like a lightning strike, is an electrical phenomenon. A nerve impulse occurs because of a difference in electrical charge across the plasma membrane of a neuron. How does this difference in electrical charge come about? The answer involves , which are electrically-charged or .
Resting Potential
When a is not actively transmitting a nerve impulse, it is in a resting state, ready to transmit a nerve impulse. During the resting state, the maintains a difference in charge across the of the neuron. The sodium-potassium pump is a mechanism of that moves sodium ions (Na+) out of cells and potassium ions (K+) into cells. The sodium-potassium pump moves both ions from areas of lower to higher concentration, using energy in and carrier proteins in the cell membrane. The video below, "Sodium Potassium Pump" by Amoeba Sisters, describes in greater detail how the sodium-potassium pump works. Sodium is the principal ion in the fluid outside of cells, and potassium is the principal ion in the fluid inside of cells. These differences in concentration create an electrical gradient across the cell membrane, called resting potentialno post. Tightly controlling membrane resting potential is critical for the transmission of nerve impulses.
https://www.youtube.com/watch?v=7NY6XdPBhxo
Sodium Potassium Pump, Amoeba Sisters, 2020.
Action Potential
A nerve impulse is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. The reversal of charge is called an . It begins when the neuron receives a chemical signal from another cell or some other type of . If the stimulus is strong enough to reach , an action potential will take place is a cascade along the axon.
This reversal of charges ripples down the axon of the neuron very rapidly as an electric current, which is illustrated in the diagram below (Figure 8.4.2). A nerve impulse is an all-or-nothing response depending on if the stimulus input was strong enough to reach threshold. If a neuron responds at all, it responds completely. A greater stimulation does not produce a stronger impulse.
In neurons with a myelin sheath on their axon, ions flow across the membrane only at the nodes between sections of myelin. As a result, the action potential appears to jump along the axon membrane from node to node, rather than spreading smoothly along the entire membrane. This increases the speed at which the action potential travels.
Transmitting Nerve Impulses
The place where an axon terminal meets another cell is called a . This is where the transmission of a nerve impulse to another cell occurs. The cell that sends the nerve impulse is called the , and the cell that receives the nerve impulse is called the .
Some synapses are purely electrical and make direct electrical connections between neurons. Most synapses, however, are chemical synapses. Transmission of nerve impulses across chemical synapses is more complex.
Chemical Synapses
At a chemical synapse, both the presynaptic and postsynaptic areas of the cells are full of molecular machinery that is involved in the transmission of nerve impulses. As shown in Figure 8.4.3, the presynaptic area contains many tiny spherical vessels called that are packed with chemicals called . When an reaches the axon terminal of the presynaptic cell, it opens channels that allow calcium to enter the terminal. Calcium causes synaptic vesicles to fuse with the membrane, releasing their contents into the narrow space between the presynaptic and postsynaptic membranes. This area is called the . The neurotransmitter molecules travel across the synaptic cleft and bind to receptors, which are proteins embedded in the membrane of the postsynaptic cell.
Neurotransmitters and Receptors
There are more than a hundred known neurotransmitters, and more than one type of neurotransmitter may be released at a given synapse by a presynaptic cell. For example, it is common for a faster-acting neurotransmitter to be released, along with a slower-acting neurotransmitter. Many neurotransmitters also have multiple types of to which they can bind. Receptors, in turn, can be divided into two general groups: chemically gated ion channels and second messenger systems.
- When a chemically gated ion channel is activated, it forms a passage that allows specific types of ions to flow across the cell membrane. Depending on the type of ion, the effect on the target cell may be or .
- When a second messenger system is activated, it starts a cascade of molecular interactions inside the target cell. This may ultimately produce a wide variety of complex effects, such as increasing or decreasing the sensitivity of the cell to stimuli, or even altering gene transcription.
The effect of a neurotransmitter on a postsynaptic cell depends mainly on the type of receptors that it activates, making it possible for a particular neurotransmitter to have different effects on various target cells. A neurotransmitter might excite one set of target cells, inhibit others, and have complex modulatory effects on still others, depending on the type of receptors. However, some neurotransmitters have relatively consistent effects on other cells. Consider the two most widely used neurotransmitters, and (gamma-aminobutyric acid). Glutamate receptors are either excitatory or modulatory in their effects, whereas GABA receptors are all inhibitory in their effects in adults.
Problems with neurotransmitters or their receptors can cause neurological disorders. The disease myasthenia gravis, for example, is caused by from the immune system blocking receptors for the neurotransmitter in postsynaptic muscle cells. This inhibits the effects of acetylcholine on muscle contractions, producing symptoms, such as muscle weakness and excessive fatigue during simple activities. Some mental illnesses (including depression) are caused, at least in part, by imbalances of certain neurotransmitters in the brain. One of the neurotransmitters involved in depression is thought to be , which normally helps regulate mood, among many other functions. Some antidepressant drugs are thought to help alleviate depression in many patients by normalizing the activity of serotonin in the brain.
8.4 Summary
- A is an electrical phenomenon that occurs because of a difference in electrical charge across the plasma membrane of a neuron.
- The maintains an electrical gradient across the plasma membrane of a neuron when it is not actively transmitting a nerve impulse. This gradient is called the resting potentialno post of the neuron.
- An is a sudden reversal of the electrical gradient across the plasma membrane of a resting neuron. It begins when the neuron receives a chemical signal from another cell or some other type of stimulus. The action potential travels rapidly down the neuron’s axon as an electric current and occurs in three stages: Depolarization, Repolarization and Recovery.
- A nerve impulse is transmitted to another cell at either an electrical or a chemical . At a chemical synapse, chemicals are released from the presynaptic cell into the synaptic cleft between cells. The chemicals travel across the cleft to the postsynaptic cell and bind to receptors embedded in its membrane.
- There are many different types of neurotransmitters. Their effects on the postsynaptic cell generally depend on the type of receptor they bind to. The effects may be excitatory, inhibitory, or modulatory in more complex ways. Both physical and mental disorders may occur if there are problems with neurotransmitters or their receptors.
8.4 Review Questions
- Define nerve impulse.
- What is the resting potential of a neuron, and how is it maintained?
- Explain how and why an action potential occurs.
- Outline how a signal is transmitted from a presynaptic cell to a postsynaptic cell at a chemical synapse.
- What generally determines the effects of a neurotransmitter on a postsynaptic cell?
- Identify three general types of effects that neurotransmitters may have on postsynaptic cells.
- Explain how an electrical signal in a presynaptic neuron causes the transmission of a chemical signal at the synapse.
- The flow of which type of ion into a neuron results in an action potential? How do these ions get into the cell? What does this flow of ions do to the relative charge inside the neuron compared to the outside?
- Name three neurotransmitters.
8.4 Explore More
https://www.youtube.com/watch?v=FEHNIELPb0s
Action Potentials, Teacher's Pet, 2018.
https://www.youtube.com/watch?v=rBcU_apy0h8
TED Ed| What is depression? - Helen M. Farrell, Parta Learning, 2017.
https://youtu.be/ZE8sRMZ5BCA
5 Weird Involuntary Behaviors Explained!, It's Okay To Be Smart, 2015.
Attributions
Figure 8.4.1
Lightening/ Purple Lightning, Dee Why by Jeremy Bishop on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 8.4.2
Action Potential by CNX OpenStax, Biology on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 8.4.3
Chemical_synapse_schema_cropped by Looie496 created file (adapted from original from US National Institutes of Health, National Institute on Aging) is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Amoeba Sisters. (2020, January 29). Sodium potassium pump. YouTube. https://www.youtube.com/watch?v=7NY6XdPBhxo&feature=youtu.be
CNX OpenStax. (2016, May 27) Figure 4 The
It's Okay To Be Smart. (2015, January 26). 5 Weird involuntary behaviors explained! YouTube. https://www.youtube.com/watch?v=ZE8sRMZ5BCA&feature=youtu.be
Mayo Clinic Staff. (n.d.). Depression (major depressive disorder) [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/depression/symptoms-causes/syc-20356007
Mayo Clinic Staff. (n.d.). Myasthenia gravis [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/myasthenia-gravis/symptoms-causes/syc-20352036
National Institute on Aging. (2006, April 8). Alzheimers disease: Unraveling the mystery. National Institutes of Health. https://www.nia.nih.gov/ (archived version)
Parta Learning. (2017, December 8). TED Ed| What is depression? - Helen M. Farrell. YouTube. https://www.youtube.com/watch?v=rBcU_apy0h8&t=291s
Teacher's Pet. (2018, August 26). Action potentials. YouTube. https://www.youtube.com/watch?v=FEHNIELPb0s&feature=youtu.be
Danger! Acid!
You probably know that batteries contain dangerous chemicals, including strong . Strong acids can hurt you if they come into contact with your skin or eyes. Therefore, it may surprise you to learn that your life depends on acids. There are many acids inside your body, and some of them are as strong as battery acid. Acids are needed for digestion and some forms of production. Genes are made of , proteins of , and lipids of .
Water and Solutions
Acids (such as battery acid) are solutions. A is a mixture of two or more substances that has the same composition throughout. Many solutions are a mixture of water and some other substance. Not all solutions are acids. Some are bases and some are neither acids nor bases. To understand acids and bases, you need to know more about pure water.
In pure water (such as distilled water), a tiny fraction of water molecules naturally breaks down to form ions. An ion is an electrically charged atom or molecule. The breakdown of water is represented by the chemical equation:
2 H2O → H3O+ + OH-
The products of this reaction are a hydronium ion (H3O+) and a hydroxide ion (OH-). The hydroxide ion, which has a negative charge, forms when a water molecule gives up a positively charged hydrogen ion (H+). The , which has a positive charge, forms when another water molecule accepts the hydrogen ion.
Acidity and pH
The concentration of hydronium ions in a solution is known as . In pure water, the concentration of hydronium ions is very low; only about one in ten million water molecules naturally breaks down to form a hydronium ion. As a result, pure water is essentially neutral. is measured on a scale called , as shown in Figure 3.12.2. Pure water has a pH of 7, so the point of neutrality on the pH scale is 7.
This pH scale shows the acidity of many common substances. The lower the pH value, the more a substance is.
Acids
If a solution has a higher concentration of s than pure water, it has a pH lower than 7. A solution with a pH lower than 7 is called an . As the hydronium ion concentration increases, the pH value decreases. Therefore, the more acidic a solution is, the lower its pH value is.
Did you ever taste vinegar? Like other acids, it tastes sour. Stronger acids can be harmful to organisms. Even stomach acid would eat through the stomach if it were not lined with a layer of mucus. Strong acids can also damage materials, even hard materials such as glass.
Bases
If a solution has a lower concentration of hydronium ions than pure water, it has a pH higher than 7. A solution with a pH higher than 7 is called a . Bases, such as baking soda, have a bitter taste. Like strong acids, strong bases can harm organisms and damage materials. For example, lye can burn the skin, and bleach can remove the colour from clothing.
Buffers
A bufferno post is a solution that can resist changes in pH. Buffers are able to maintain a certain pH by by absorbing any H+ or OH- ions added to the solution. Buffers are extremely important in biological systems in order to maintain a pH conducive to life. Bicarbonate is an example of a buffer which is used to maintain pH of the blood. In this buffering system, if blood becomes too acidic, carbonic acid will convert to carbon dioxide and water. If the blood becomes too basic, carbonic acid will convert to bicarbonate and H+ ions:
CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
Acids, Bases, and Enzymes
Many acids and bases in living things provide the pH that need. Enzymes are biological catalysts that must work effectively for to occur. Most enzymes can do their job only at a certain level of acidity. secrete and to maintain the proper pH for enzymes to do their work.
Every time you digest food, acids and bases are at work in your digestive system. Consider the enzyme pepsin, which helps break down in the stomach. Pepsin needs an environment to do its job. The stomach secretes a strong called hydrochloric acid that allows pepsin to work. When stomach contents enter the small intestine, the acid must be neutralized, because enzymes in the small intestine need a basic environment in order to work. An organ called the pancreas secretes a named bicarbonate into the small intestine, and this base neutralizes the acid.
Feature: My Human Body
Do you ever have heartburn? The answer is probably "yes." More than 60 million Americans have heartburn at least once a month, and more than 15 million suffer from it on a daily basis. Knowing more about heartburn may help you prevent it or know when it's time to seek medical treatment.
Heartburn doesn't have anything to do with the heart, but it does cause a burning sensation in the vicinity of the chest. Normally, the acid secreted into the stomach remains in the stomach where it is needed to allow pepsin to do its job of digesting proteins. A long tube called the esophagus carries food from the mouth to the stomach. A sphincter, or valve, between the esophagus and stomach opens to allow swallowed food to enter the stomach and then closes to prevent stomach contents from backflowing into the esophagus. If this sphincter is weak or relaxes inappropriately, stomach contents flow into the esophagus. Because stomach contents are usually acidic, this causes the burning sensation known as heartburn. People who are prone to heartburn and suffer from it often may be diagnosed with GERD, which stands for gastroesophageal reflux disease.
GERD — as well as occasional heartburn — often can be improved by dietary and other lifestyle changes that decrease the amount and acidity of reflux from the stomach into the esophagus.
- Some foods and beverages seem to contribute to GERD, so these should be avoided. Problematic foods include chocolate, fatty foods, peppermint, coffee, and alcoholic beverages.
- Decreasing portion size and eating the last meal of the day at least a couple of hours before bedtime may reduce the risk of reflux occurring.
- Smoking tends to weaken the lower esophageal sphincter, so quitting the habit may help control reflux.
- GERD is often associated with being overweight. Losing weight often brings improvement.
- Some people are helped by sleeping with the head of the bed elevated. This allows gravity to help control the backflow of acids into the esophagus from the stomach.
If you have frequent heartburn and lifestyle changes don't help, you may need medication to control the condition. Over-the-counter (OTC) antacids may be all that you need to control the occasional heartburn attack. OTC medications are usually bases that neutralize stomach acids. They may also create bubbles that help block stomach contents from entering the esophagus. For some people, OTC medications are not enough, and prescription medications are instead required for the control of GERD. These prescription medications generally work by inhibiting acid secretion in the stomach.
Be sure to see a doctor if you can't control your heartburn, or you have it often. Untreated GERD not only interferes with quality of life, it may also lead to more serious complications, ranging from esophageal bleeding to esophageal cancer.
3.12 Summary
- A is a mixture of two or more substances that has the same composition throughout. Many solutions consist of water and one or more dissolved substances.
- is a measure of the hydronium ion concentration in a solution. Pure water has a very low concentration and a pH of 7, which is the point of neutrality on the .
- Acids have a higher hydronium ion concentration than pure water and a pH lower than 7. Bases have a lower hydronium ion concentration than pure water and a pH higher than 7.
- Many acids and bases in living things are secreted to provide the proper pH for enzymes to work properly. Enzymes are the biological catalysts (like pepsin) needed to digest protein in the stomach. Pepsin requires an acidic environment.
3.12 Review Questions
- What is a solution?
- Define acidity.
- Explain how acidity is measured.
- Compare and contrast acids and bases.
- Hydrochloric acid is secreted by the stomach to provide an acidic environment for the enzyme pepsin. What is the pH of this acid? How strong of an acid is it compared with other acids?
- Define an ion. Identify the ions in the equation below, and explain what makes them ions:
- 2 H2O → H3O+ + OH-
- Explain why the pancreas secretes bicarbonate into the small intestine.
- Do you think pepsin would work in the small intestine? Why or why not?
- You may have mixed vinegar and baking soda and noticed that they bubble and react with each other. Explain why this happens. Explain also what happens to the pH of this solution after you mix the vinegar and baking soda.
- Pregnancy hormones can cause the lower esophageal sphincter to relax. What effect do you think this has on pregnant women? Explain your answer.
3.12 Explore More
https://www.youtube.com/watch?v=rIvEvwViJGk&feature=youtu.be
pH and Buffers by Bozeman Science, 2014.
https://www.youtube.com/watch?v=DupXDD87oHc&feature=youtu.be
The strengths and weaknesses of acids and bases - George Zaidan and Charles Morton, TED-Ed, 2013.
Attributions
Figure 3.12.1
Leaky battery by Carbon Arc on Flickr is used under a CC BY-NC-SA 2.0 (https://creativecommons.org/licenses/by-nc-sa/2.0/) license.
Figure 3.12.2
PH_Scale by Christinelmiller on Wikimedia Commons is used under a © CC0 1.0 (https://creativecommons.org/publicdomain/zero/1.0/) public domain dedication license.
Figure 3.12.3
Ph scale with examples by OpenStax College, on Wikimedia Commons, is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
Figure 3.12.4
GERD by BruceBlaus on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
References
Betts, J.G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, April 25). Figure 26.15 The pH Scale [digital image]. In Anatomy and Physiology. OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/26-4-acid-base-balance
Bozeman Science. (2014, February 22). pH and buffers. YouTube. https://www.youtube.com/watch?v=rIvEvwViJGk&feature=youtu.be
TED-Ed. (2013, October 24). The strengths and weaknesses of acids and bases - George Zaidan and Charles Morton. YouTube. https://www.youtube.com/watch?v=DupXDD87oHc&feature=youtu.be
Created by: CK-12/Adapted by Christine Miller
Like Father, Like Son
This father-son duo share some similarities. The shape of their faces and their facial features look very similar. If you saw them together, you might well guess that they are father and son. People have long known that the characteristics of living things are similar between parents and their offspring. However, it wasn’t until the experiments of Gregor Mendel that scientists understood how those traits are inherited.
The Father of Genetics
Mendel did experiments with pea plants to show how traits such as seed shape and flower colour are inherited. Based on his research, he developed his two well known laws of inheritance: the and the . When Mendel died in 1884, his work was still virtually unknown. In 1900, three other researchers working independently came to the same conclusions that Mendel had drawn almost half a century earlier. Only then was Mendel's work rediscovered.
Mendel knew nothing about genes, because they were discovered after his death. He did think, however, that some type of "factors" controlled traits, and that those "factors" were passed from parents to offspring. We now call these "factors" genes. , now expressed in terms of genes, form the basis of , the science of heredity. For this reason, Mendel is often called the father of genetics.
The Language of Genetics
Today, we know that traits of organisms are controlled by on . To talk about inheritance in terms of genes and chromosomes, you need to know the language of genetics. The terms below serve as a good starting point. They are illustrated in the figure that follows.
- A is the part of a that contains the genetic code for a given . For example, in pea plants, a given gene might code for flower colour.
- The position of a given gene on a chromosome is called its (plural, loci). A gene might be located near the center, or at one end or the other of a .
- A given gene may have different normal versions, which are called . For example, in pea plants, there is a purple-flower allele (B) and a white-flower allele (b) for the flower-colour gene. Different alleles account for much of the variation in the traits of organisms, including people.
- In sexually reproducing organisms, each individual has two copies of each type of chromosome. Paired chromosomes of the same type are called . They are about the same size and shape, and they have all the same genes at the same loci.
Genotype
When occurs, sex cells (called ) unite during to form a single cell called a . The zygote inherits two of each type of chromosome, with one chromosome of each type coming from the father, and the other coming from the mother. Because have the same genes at the same loci, each individual also inherits two copies of each gene. The two copies may be the same allele or different . The alleles an individual inherits for a given gene make up the individual’s . As shown in Table 5.11.1, an organism with two of the same allele (for example, BB or bb) is called a . An organism with two different alleles (in this example, Bb) is called a .
Table 5.11.1
Allele Combinations Associated With the Terms Homozygous and Heterozygous
Phenotype
The expression of an organism’s genotype is referred to as its , and it refers to the organism’s traits, such as purple or white flowers in pea plants. As you can see from Table 5.11.1, different genotypes may produce the same phenotype. In this example, both BB and Bb genotypes produce plants with the same phenotype, purple flowers. Why does this happen? In a Bb heterozygote, only the B allele is expressed, so the b allele doesn’t influence the phenotype. In general, when only one of two alleles is expressed in the phenotype, the expressed allele is called , and the allele that isn’t expressed is called .
The terms dominant and recessive may also be used to refer to phenotypic traits. For example, purple flower colour in pea plants is a dominant trait. It shows up in the phenotype whenever a plant inherits even one dominant allele for the trait. Similarly, white flower colour is a recessive trait. Like other recessive traits, it shows up in the phenotype only when a plant inherits two recessive alleles for the trait.
5.11 Summary
- Mendel's laws of inheritance, now expressed in terms of , form the basis of genetics, which is the science of heredity. This is why Mendel is often called the father of genetics.
- A gene is the part of a that codes for a given . The position of a gene on a chromosome is its . A given gene may have different versions, called . Paired chromosomes of the same type are called . They have the same size and shape, and they have the same genes at the same .
- The alleles an individual inherits for a given gene make up the individual's . An organism with two of the same allele is called a homozygote, and an individual with two different alleles is called a heterozygote.
- The expression of an organism's genotype is referred to as its . A dominant allele is always expressed in the phenotype, even when just one dominant allele has been inherited. A recessive allele is expressed in the phenotype only when two recessive alleles have been inherited.
5.11 Review Questions
- Define genetics.
- Why is Gregor Mendel called the father of genetics if genes were not discovered until after his death?
- Imagine that there are two alleles, R and r, for a given gene. R is dominant to r. Answer the following questions about this gene:
- What are the possible homozygous and heterozygous genotypes?
- Which genotype or genotypes express the dominant R phenotype? Explain your answer.
- Are R and r on different loci? Why or why not?
- Can R and r be on the same exact chromosome? Why or why not? If not, where are they located?
5.11 Explore More
https://www.youtube.com/watch?v=pv3Kj0UjiLE
Alleles and Genes, Amoeba Sisters, 2018.
https://www.youtube.com/watch?v=OaovnS7BAoc
Genotypes and Phenotypes, Bozeman Science, 2011.
Attributions
Figure 5.11.1
Father holding his baby boy with matching haircut [photo] by Kelly Sikkema on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 5.11.2
Chromosome, Gene, Locus, and Allele by CK-12 Foundation is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.
©CK-12 Foundation Licensed under • Terms of Use • Attribution
Table 5.11.1
Allele Combinations Associated With the Terms Homozygous and Heterozygous by Christine Miller is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Amoeba Sisters. (2018, February 1). Alleles and genes. YouTube. https://www.youtube.com/watch?v=pv3Kj0UjiLE&feature=youtu.be
Bozeman Science. (2011, August 4). Genotypes and phenotypes. YouTube. https://www.youtube.com/watch?v=OaovnS7BAoc&feature=youtu.be
Brainard, J/ CK-12 Foundation. (2016). Figure 2 Chromosome, gene, locus, and allele [digital image]. In CK-12 College Human Biology (Section 5.10) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-human-biology/section/5.9/
Created by CK-12 Foundation/Adapted by Christine Miller
It’s All about Sex
A tiny from dad breaks through the surface of a huge egg from mom. Voilà! In nine months, a new son or daughter will be born. Like most other multicellular organisms, human beings reproduce sexually. In human sexual reproduction, males produce sperm and females produce eggs, and a new offspring forms when a sperm unites with an egg. How do sperm and eggs form? And how do they arrive together at the right place and time so they can unite to form a new offspring? These are functions of the reproductive system.
What Is the Reproductive System?
The is the human organ system responsible for the production and fertilization of gametes (sperm or eggs) and, in females, the carrying of a fetus. Both male and female reproductive systems have organs called s that produce gametes. A is a cell that combines with another haploid gamete during , forming a single diploid cell called a . Besides producing gametes, the gonads also produce sex hormones. are endocrine hormones that control the development of sex organs before birth, sexual maturation at puberty, and reproduction once sexual maturation has occurred. Other reproductive system organs have various functions, such as maturing gametes, delivering gametes to the site of fertilization, and providing an environment for the development and growth of an offspring.
Sex Differences in the Reproductive System
The reproductive system is the only human organ system that is significantly different between males and females. Embryonic structures that will develop into the reproductive system start out the same in males and females, but by birth, the reproductive systems have differentiated. How does this happen?
Sex Differentiation
Starting around the seventh week after conception in genetically male (XY) embryos, a gene called SRY on the Y chromosome (shown in Figure 18.2.2) initiates the production of multiple proteins. These proteins cause undifferentiated gonadal tissue to develop into male gonads (testes). The male gonads then secrete hormones — including the male sex hormone testosterone — that trigger other changes in the developing offspring (now called a fetus), causing it to develop a complete male reproductive system. Without a Y chromosome, an embryo will develop female gonads (ovaries) that will produce the female sex hormone estrogen. Estrogen, in turn, will lead to the formation of the other organs of a normal female reproductive system.
Homologous Structures
Undifferentiated embryonic tissues develop into different structures in male and female . Structures that arise from the same tissues in males and females are called s. The male testes and female ovaries, for example, are homologous structures that develop from the undifferentiated gonads of the embryo. Likewise, the male penis and female clitoris are homologous structures that develop from the same embryonic tissues.
Sex Hormones and Maturation
Male and female reproductive systems are different at birth, but they are immature and incapable of producing gametes or sex hormones. Maturation of the reproductive system occurs during puberty, when hormones from the and stimulate the testes or ovaries to start producing sex hormones again. The main sex hormones are in males and in females. Sex hormones, in turn, lead to the growth and maturation of the reproductive organs, rapid body growth, and the development of secondary sex characteristics. s are traits that are different in mature males and females, but are not directly involved in reproduction. They include facial hair in males and breasts in females.
Male Reproductive System
The main structures of the male reproductive system are external to the body and illustrated in Figure 18.2.3. The two (singular, testis) hang between the thighs in a sac of skin called the . The testes produce both and . Resting atop each testis is a coiled structure called the (plural, epididymes). The function of the epididymes is to mature and store sperm. The is a tubular organ that contains the urethra and has the ability to stiffen during sexual arousal. Sperm passes out of the body through the urethra during a sexual climax (orgasm). This release of sperm is called ejaculation.
In addition to these organs, the male reproductive system consists of several ducts and glands that are internal to the body. The ducts, which include the (also called the ductus deferens), transport sperm from the to the . The glands, which include the and , produce fluids that become part of semen. is the fluid that carries sperm through the urethra and out of the body. It contains substances that control pH and provide sperm with nutrients for energy.
Female Reproductive System
The main structures of the female reproductive system are internal to the body and shown in the following figure. They include the paired , which are small, ovoid structures that produce and secrete . The two (sometimes called Fallopian tubes or uterine tubes) start near the ovaries and end at the . Their function is to transport ova from the ovaries to the uterus. If an egg is fertilized, it usually occurs while it is traveling through an oviduct. The uterus is a pear-shaped muscular organ that functions to carry a fetus until birth. It can expand greatly to accommodate a growing fetus, and its muscular walls can contract forcefully during labour to push the baby out of the uterus and into the vagina. The is a tubular tract connecting the uterus to the outside of the body. The vagina is where sperm are usually deposited during and . The vagina is also called the birth canal because a baby travels through the vagina to leave the body during birth.
The external structures of the female reproductive system are referred to collectively as the . They include the , which is homologous to the male penis. They also include two pairs of (singular, labium), which surround and protect the openings of the urethra and vagina.
18.2 Summary
- The is the human organ system responsible for the production and of and, in females, the carrying of a .
- Both male and female reproductive systems have organs called ( in males, in females) that produce gametes ( or ova) and sex hormones (such as in males and in females). Sex are endocrine hormones that control the prenatal development of reproductive organs, sexual maturation at puberty, and reproduction after .
- The reproductive system is the only organ system that is significantly different between males and females. A Y-chromosome gene called SRY is responsible for undifferentiated embryonic tissues developing into a male reproductive system. Without a Y chromosome, the undifferentiated embryonic tissues develop into a female reproductive system.
- Structures such as testes and ovaries that arise from the same undifferentiated embryonic tissues in males and females are called .
- Male and female reproductive systems are different at birth, but at that point, they are immature and nonfunctioning. Maturation of the reproductive system occurs during puberty, when hormones from the and stimulate the gonads to produce sex hormones again. The sex hormones, in turn, cause the changes of puberty.
- Male reproductive system organs include the , , , , , and .
- Female reproductive system organs include the , , , , , and .
18.2 Review Questions
- What is the reproductive system?
- Explain the difference between the vulva and the vagina.
18.2 Explore More
https://youtu.be/kMWxuF9YW38
Sex Determination: More Complicated Than You Thought, TED-Ed, 2012.
https://youtu.be/vcPJkz-D5II
The evolution of animal genitalia - Menno Schilthuizen, TED-Ed, 2017.
https://youtu.be/l5knvmy1Z3s
Hormones and Gender Transition, Reactions, 2015.
Attributions
Figure 18.2.1
Sperm-egg by Unknown author on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/public_domain).
Figure 18.2.2
Y Chromosome by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.3
3D_Medical_Animation_Vas_Deferens by https://www.scientificanimations.com on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 18.2.4
Blausen_0399_FemaleReproSystem_01 by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.
References
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.
Reactions. (2015, June 8). Hormones and gender transition. YouTube. https://www.youtube.com/watch?v=l5knvmy1Z3s&feature=youtu.be
TED-Ed. (2012, April 23). Sex determination: More complicated than you thought. YouTube. https://www.youtube.com/watch?v=kMWxuF9YW38&feature=youtu.be
TED-Ed. (2017, April 24). The evolution of animal genitalia - Menno Schilthuizen. YouTube. https://www.youtube.com/watch?v=vcPJkz-D5II&feature=youtu.be