7.1 Case Study: Under Pressure
Looking at this photo of a football game (Figure 7.1.1), you can see why it is so important that the players wear helmets. As players tackle each other, football often involves forceful impact to the head. This can cause damage to the brain — temporarily (as in the case of a concussion) or long-term and more severe. Helmets are critical in reducing the incidence of (TBIs), but they do not fully prevent them.
As a former professional football player who also played in college and high school, 43-year-old Jayson sustained many high-impact head injuries over the course of his football playing years. A few years ago, Jayson began experiencing a variety of troubling symptoms, including the loss of bladder control (the involuntary leakage of urine), memory loss, and difficulty walking. Symptoms like these are often signs of damage to the nervous system, which includes the brain, spinal cord, and nerves, but they can result from many different types of injuries or diseases that affect the nervous system. In order to treat him properly, Jayson’s doctors needed to do several tests to determine the exact cause of his symptoms. The doctors ordered a spinal tap to see if he had an infection, and an MRI (magnetic resonance imaging) to see if there were any observable problems in and around his brain.
The MRI revealed the cause of Jayson’s symptoms. There are fluid-filled spaces within the brain called ventricles, and compared to normal ventricles, Jayson’s ventricles were enlarged. Based on this observation, along with the results of other tests, Jayson’s doctor diagnosed him with , a term that literally means “water head.” Hydrocephalus occurs when the fluid that fills the ventricles — called cerebrospinal fluid — builds up excessively, causing the ventricles to become enlarged. This puts pressure on the brain, which can cause a variety of neurological symptoms, including the ones Jayson was experiencing. In Figure 7.1.2, you can see the difference between normal ventricles and ventricles that are enlarged due to hydrocephalus. Notice in the image on the right how the brain becomes “squeezed” due to hydrocephalus.
Hydrocephalus often occurs at birth, as a result of genetic factors or events that occurred during fetal development. Because babies are born with skull bones that are not fully fused, the skull of a baby born with hydrocephalus can expand and relieve some of the pressure on the brain, as reflected in the enlarged head size shown in Figure 7.1.2. Adults have fully fused, inflexible skulls, so when hydrocephalus occurs in an adult, the brain experiences all of the increased pressure.
Why did Jayson develop hydrocephalus? There are many possible causes of hydrocephalus in adults, including tumors, infections, hemorrhages, and TBIs. Given his repeated and long history of football-related TBIs and the absence of any evidence of infection, tumor, or other cause, Jayson’s doctor thinks his head injuries were most likely responsible for his hydrocephalus.
Although hydrocephalus is serious, there are treatments. Read the rest of this chapter to learn about the cells, tissues, organs, cavities, and systems of the body, how they are interconnected, and the importance of keeping the body in a state of (or balance). The amount of cerebrospinal fluid in the ventricles is normally kept at a relatively steady level, and the potentially devastating symptoms of hydrocephalus are an example of what can happen when a system in the body becomes unbalanced. At the end of the chapter, you will learn about Jayson’s treatment and prognosis.
Chapter Overview: Introduction to the Human Body
In this chapter, you will learn about the general organization and functions of the human body. Specifically, you will learn about:
- The organization of the body from and up through , tissues, organs, and organ systems.
- How organ systems work together to carry out the functions of life.
- The variety of different specialized cell types in humans, the four major types of human tissues, and some of their functions.
- The five vital organs and the 11 major organ systems of the human body.
- Spaces in the body called body cavities, and the organs they hold and protect.
- The tissues and fluid that protect the brain and spinal cord.
- How organ systems communicate and interact in body processes, such as cellular respiration, digestion, the fight-or-flight response to stressors, and physical activities (such as sports).
- How homeostasis is maintained to keep the body in a relatively steady state, and the problems that can be caused by loss of homeostasis, such as diabetes.
As you read the chapter, think about the following questions:
- What is the normal function of cerebrospinal fluid?
- What is a spinal tap and how does it test for infection?
- In Jayson’s case, what organs and organ systems are probably affected by his hydrocephalus? What are some ways in which these organ systems interact?
- The level of cerebrospinal fluid is normally kept in a state of homeostasis. What are other examples of types of homeostasis that keep your body functioning properly?
Attributions
Figure 7.1.1.
Football tackel [photo] by John Torcasio on Unsplash is used under the Unsplash License (https://unsplash.com/license).
Figure 7.1.2
Hydrocephalus by Centers for Disease Control and Prevention (CDC) on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).
References
Mayo Clinic Staff. (n.d.). Hydrocephalus [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/hydrocephalus/symptoms-causes/syc-20373604
Mayo Clinic Staff. (n.d.). Traumatic brain injury [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/traumatic-brain-injury/symptoms-causes/syc-20378557
Created by CK-12 Foundation/Adapted by Christine Miller
Steady as She Goes
This device (Figure 7.8.1) looks simple, but it controls a complex system that keeps a home at a steady temperature — it's a thermostat. The device shows the current temperature in the room, and also allows the occupant to set the thermostat to the desired temperature. A thermostat is a commonly cited model of how living systems — including the human body— maintain a steady state called homeostasis.
What Is Homeostasis?
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 , , , and throughout the body to maintain many different variables within narrow ranges compatible with life. Keeping a stable internal environment requires continually monitoring the internal environment and constantly making adjustments to keep things in balance.
Set Point and Normal Range
For any given variable, such as body temperature or blood glucose level, there is a particular that is the physiological optimum value. The set point for human body temperature, for example, is about 37 degrees C (98.6 degrees F). As the body works to maintain for temperature or any other internal variable, the value typically fluctuates around the set point. Such fluctuations are normal, as long as they do not become too extreme. The spread of values within which such fluctuations are considered insignificant is called the . In the case of body temperature, for example, the normal range for an adult is about 36.5 to 37.5 degrees C (97.7 to 99.5 degrees F).
A good analogy for set point, normal range, and maintenance of homeostasis is driving. When you are driving a vehicle on the road, you are supposed to drive in the centre of your lane — this is analogous to the . Sometimes, you are not driving in the exact centre of the lane, but you are still within your lines, so you are in the equivalent of the . However, if you were to get too close to the centre line or the shoulder of the road, you would take action to correct your position. You'd move left if you were too close to the shoulder, or right if too close to the centre line — which is analogous to our next concept, to maintain .
Maintaining Homeostasis
is normally maintained in the human body by an extremely complex balancing act. Regardless of the variable being kept within its normal range, maintaining homeostasis requires at least four interacting components: stimulus, sensor, control centre, and effector.
- The is provided by the variable being regulated. Generally, the stimulus indicates that the value of the variable has moved away from the set point or has left the normal range.
- The monitors the values of the variable and sends data on it to the control centre.
- The matches the data with normal values. If the value is not at the set point or is outside the normal range, the control centre sends a signal to the effector.
- The is an organ, gland, muscle, or other structure that acts on the signal from the control centre to move the variable back toward the set point.
Each of these components is illustrated in Figure 7.8.2. The diagram on the left is a general model showing how the components interact to maintain homeostasis. The diagram on the right shows the example of body temperature. From the diagrams, you can see that maintaining homeostasis involves feedback, which is data that feeds back to control a response. Feedback may be negative (as in the example below) or positive. All the feedback mechanisms that maintain homeostasis use . Biological examples of positive feedback are much less common.
Negative Feedback
In a , feedback serves to reduce an excessive response and keep a variable within the . Two processes controlled by negative feedback are body temperature regulation and control of blood glucose.
Body Temperature
Body temperature regulation involves , whether it lowers the temperature or raises it, as shown in Figure 7.8.3 and explained in the text that follows.
Cooling Down
The human body’s temperature regulatory centre is the in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher than the , it sets into motion the following responses:
- Blood vessels in the skin dilate (vasodilation) to allow more blood from the warm body core to flow close to the surface of the body, so heat can be radiated into the environment.
- As blood flow to the skin increases, sweat glands in the skin are activated to increase their output of sweat (diaphoresis). When the sweat evaporates from the skin surface into the surrounding air, it takes heat with it.
- Breathing becomes deeper, and the person may breathe through the mouth instead of the nasal passages. This increases heat loss from the lungs.
Heating Up
When the brain’s temperature regulatory centre receives data that body temperature is lower than the set point, it sets into motion the following responses:
- Blood vessels in the skin contract (vasoconstriction) to prevent blood from flowing close to the surface of the body, which reduces heat loss from the surface.
- As temperature falls lower, random signals to skeletal muscles are triggered, causing them to contract. This causes shivering, which generates a small amount of heat.
- The may be stimulated by the brain (via the pituitary gland) to secrete more thyroid hormone. This hormone increases metabolic activity and heat production in cells throughout the body.
- The may also be stimulated to secrete the hormone . This hormone causes the breakdown of glycogen (the carbohydrate used for energy storage in animals) to , which can be used as an energy source. This catabolic chemical process is , or heat producing.
Blood Glucose
In controlling the blood glucose level, certain endocrine cells in the pancreas (called alpha and beta cells) detect the level of glucose in the blood. They then respond appropriately to keep the level of blood glucose within the normal range.
- If the blood glucose level rises above the normal range, pancreatic beta cells release the hormone insulin into the bloodstream. Insulin signals cells to take up the excess glucose from the blood until the level of blood glucose decreases to the normal range.
- If the blood glucose level falls below the normal range, pancreatic alpha cells release the hormone glucagon into the bloodstream. Glucagon signals cells to break down stored glycogen to glucose and release the glucose into the blood until the level of blood glucose increases to the normal range.
https://www.youtube.com/watch?v=Iz0Q9nTZCw4
Homeostasis and Negative/Positive Feedback, Amoeba Sisters, 2017.
Positive Feedback
In a , feedback serves to intensify a response until an end point is reached. Examples of processes controlled by positive feedback in the human body include blood clotting and childbirth.
Blood Clotting
When a wound causes bleeding, the body responds with a positive feedback loop to clot the blood and stop blood loss. Substances released by the injured blood vessel wall begin the process of blood clotting. Platelets in the blood start to cling to the injured site and release chemicals that attract additional platelets. As the platelets continue to amass, more of the chemicals are released and more platelets are attracted to the site of the clot. The positive feedback accelerates the process of clotting until the clot is large enough to stop the bleeding.
Childbirth
Figure 7.8.6 shows the positive feedback loop that controls childbirth. The process normally begins when the head of the infant pushes against the cervix. This stimulates nerve impulses, which travel from the cervix to the hypothalamus in the brain. In response, the hypothalamus sends the hormone to the pituitary gland, which secretes it into the bloodstream so it can be carried to the uterus. Oxytocin stimulates uterine contractions, which push the baby harder against the cervix. In response, the cervix starts to dilate in preparation for the passage of the baby. This cycle of positive feedback continues, with increasing levels of oxytocin, stronger uterine contractions, and wider dilation of the cervix until the baby is pushed through the birth canal and out of the body. At that point, the cervix is no longer stimulated to send nerve impulses to the brain, and the entire process stops.
Normal childbirth is driven by a positive feedback loop. Positive feedback causes an increasing deviation from the normal state to a fixed end point, rather than a return to a normal set point as in homeostasis.
When Homeostasis Fails
Homeostatic mechanisms work continuously to maintain stable conditions in the human body. Sometimes, however, the mechanisms fail. When they do, may result, in which cells may not get everything they need or toxic wastes may accumulate in the body. If homeostasis is not restored, the imbalance may lead to disease — or even death. is an example of a disease caused by homeostatic imbalance. In the case of diabetes, blood glucose levels are no longer regulated and may be dangerously high. Medical intervention can help restore homeostasis and possibly prevent permanent damage to the organism.
Normal aging may bring about a reduction in the efficiency of the body’s control systems, which makes the body more susceptible to disease. Older people, for example, may have a harder time regulating their body temperature. This is one reason they are more likely than younger people to develop serious heat-induced illnesses, such as heat stroke.
Feature: My Human Body
is diagnosed in people who have abnormally high levels of blood glucose after fasting for at least 12 hours. A fasting level of blood glucose below 100 is normal. A level between 100 and 125 places you in the pre-diabetes category, and a level higher than 125 results in a diagnosis of diabetes.
Of the two types of diabetes, is the most common, accounting for about 90 per cent of all cases of diabetes in the United States. Type 2 diabetes typically starts after the age of 40. However, because of the dramatic increase in recent decades in obesity in younger people, the age at which type 2 diabetes is diagnosed has fallen. Even children are now being diagnosed with type 2 diabetes. Today, about 3 million Canadians (8.1% of total population) are living with diabetes.
You may at some point have your blood glucose level tested during a routine medical exam. If your blood glucose level indicates that you have diabetes, it may come as a shock to you because you may not have any symptoms of the disease. You are not alone, because as many as one in four diabetics do not know they have the disease. Once the diagnosis of diabetes sinks in, you may be devastated by the news. Diabetes can lead to heart attacks, strokes, blindness, kidney failure, nerve damage, and loss of toes or feet. The risk of death in adults with diabetes is 50 per cent greater than it is in adults without diabetes, and diabetes is the seventh leading cause of death of adults. In addition, controlling diabetes usually requires frequent blood glucose testing, watching what and when you eat, and taking medications or even insulin injections. All of this may seem overwhelming.
The good news is that changing your lifestyle may stop the progression of type 2 diabetes or even reverse it. By adopting healthier habits, you may be able to keep your blood glucose level within the normal range without medications or insulin. Here’s how:
- Lose weight. Any weight loss is beneficial. Losing as little as seven per cent of your weight may be all that is needed to stop diabetes in its tracks. It is especially important to eliminate excess weight around your waist.
- Exercise regularly. You should try to exercise for at least 30 minutes, five days a week. This will not only lower your blood sugar and help your insulin work better, but it will also lower your blood pressure and improve your heart health. Another bonus of exercise is that it will help you lose weight by increasing your basal metabolic rate.
- Adopt a healthy diet. Decrease your consumption of refined carbohydrates, such as sweets and sugary drinks. Increase your intake of fibre-rich foods, such as fruits, vegetables, and whole grains. About one-quarter of each meal should consist of high-protein foods, such as fish, chicken, dairy products, legumes, or nuts.
- Control stress. Stress can increase your blood glucose and also raise your blood pressure and risk of heart disease. When you feel stressed out, do breathing exercises or take a brisk walk or jog. Try to replace stressful thoughts with more calming ones.
- Establish a support system. Enlist the help and support of loved ones, as well as medical professionals, such as a nutritionist and diabetes educator. Having a support system will help ensure that you are on the path to wellness, and that you can stick to your plan.
7.8 Summary
- 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.
- 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.
- 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, which makes the elderly more susceptible to disease.
7.8 Review Questions
- Compare and contrast negative and positive feedback loops.
- Explain how negative feedback controls body temperature.
- Give two examples of physiological processes controlled by positive feedback loops.
- During breastfeeding, the stimulus of the baby sucking on the nipple increases the amount of milk produced by the mother. The more sucking, the more milk is usually produced. Is this an example of negative or positive feedback? Explain your answer. What do you think might be the evolutionary benefit of the milk production regulation mechanism you described?
- Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops.
- The level of a sex hormone, testosterone (T), is controlled by negative feedback. Another hormone, gonadotropin-releasing hormone (GnRH), is released by the hypothalamus of the brain, which triggers the pituitary gland to release luteinizing hormone (LH). LH stimulates the gonads to produce T. When there is too much T in the bloodstream, it feeds back on the hypothalamus, causing it to produce less GnRH. While this does not describe all the feedback loops involved in regulating T, answer the following questions about this particular feedback loop.
- What is the stimulus in this system? Explain your answer.
- What is the control centre in this system? Explain your answer.
- In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer.
7.8 Explore More
https://www.youtube.com/watch?v=LSgEJSlk6W4
Homeostasis - What Is Homeostasis - What Is Set Point For Homeostasis - Homeostasis In The Human Body, Whats Up Dude, 2017.
https://www.youtube.com/watch?v=XMsJ-3qRVJM
Attributions
Figure 7.8.1
Nest_Thermostat by Amanitamano on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) license.
Figure 7.8.2
Negative_Feedback_Loops by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
Figure 7.8.3
Body Temperature Homeostasis by OpenStax College, Biology is used under a CC BY 4.0 license.
Figure 7.8.4
Homeostasis_of_blood_sugar by Christinelmiller on Wikimedia Commons is used under a CC0 1.0 Universal Public Domain Dedication (https://creativecommons.org/publicdomain/zero/1.0/deed.en) license.
Figure 7.8.5
Positive_Feedback_Diagram_Blood_Clotting by Elliottuttle on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.
Figure 7.8.6
Pregnancy-Positive_Feedback by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/deed.en) license.
References
Amoeba Sisters. (2017, September 7). Homeostasis and negative/positive feedback. YouTube. https://www.youtube.com/watch?v=Iz0Q9nTZCw4&feature=youtu.be
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 1.10 Negative feedback loop [digital image/ diagram]. In Anatomy and Physiology (Section 1.5). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-5-homeostasis
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 1.11 Positive feedback loop normal childbirth is driven by a positive feedback loop [digital image/ diagram]. In Anatomy and Physiology (Section 1.5). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/1-5-homeostasis
Cognito. (2018, December 18). GCSE Biology - Homeostasis #38. YouTube. https://www.youtube.com/watch?v=XMsJ-3qRVJM&feature=youtu.be
Mayo Clinic Staff. (n.d.). Type 2 diabetes [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/type-2-diabetes/symptoms-causes/syc-20351193
OpenStax CNX. (2016, March 23). Figure 4 The body is able to regulate temperature in response to signals from the nervous system [digital image]. In OpenStax, Biology (Section 33.3). https://cnx.org/contents/GFy_h8cu@10.8:BP24ZReh@7/Homeostasis
Whats Up Dude. (2017, September 20). Homeostasis - What is homeostasis - What is set point for homeostasis - Homeostasis in the human body. YouTube. https://www.youtube.com/watch?v=LSgEJSlk6W4&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].
The ability of an organism to maintain constant internal conditions despite external changes.
The smallest particle of an element that still has the properties of that element.
A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.
The smallest unit of life, consisting of at least a membrane, cytoplasm, and genetic material.
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