Angela and Saloni are college students who met in physics class. They decide to study together for their upcoming midterm, but first, they want to grab some lunch. Angela says there is a particular restaurant she would like to go to, because they are able to accommodate her dietary restrictions. Saloni agrees and they head to the restaurant.

At lunch, Saloni asks Angela what is special about her diet. Angela tells her that she can’t eat gluten. Saloni says, “My cousin did that for a while because she heard that gluten is bad for you. But it was too hard for her to not eat bread and pasta, so she gave it up.” Angela tells Saloni that avoiding gluten isn’t optional for her — she has celiac disease. Eating even very small amounts of gluten could damage her digestive system.  It can be difficult for people living with celiac disease to find foods when eating out.

You have probably heard of gluten, but what is it, and why is it harmful to people with celiac disease? Gluten is a protein present in wheat and some other grains (such as barley, rye, and oats), so it is commonly found in foods like bread, pasta, baked goods, and many packaged foods, like the ones pictured in Figure 15.1.2.

Figure 15.1.2 Gluten is a protein present in foods like bread, pasta, and baked goods.

For people with celiac disease, eating gluten causes an autoimmune reaction that results in damage to the small, finger-like villi lining the small intestine, causing them to become inflamed and flattened (see Figure 15.1.3). This damage interferes with the digestive process, which can result in a wide variety of symptoms including diarrhea, anemia, skin rash, bone pain, depression, and anxiety, among others. The degree of damage to the villi can vary from mild to severe, with more severe damage generally resulting in more significant symptoms and complications. Celiac disease can have serious long-term consequences, such as osteoporosis, problems in the nervous and reproductive systems, and the development of certain types of cancers.

 

Why does celiac disease cause so many different types of symptoms and have such significant negative health consequences? As you read this chapter and learn about how the digestive system works, you will see just how important the villi of the small intestine are to the body as a whole. At the end of the chapter, you will learn more about celiac disease, why it can be so serious, and whether it is worth avoiding gluten for people who do not have a diagnosed medical issue with it.

Attributions

Figure 15.1.1

Bread [photo] by Sergio Arze on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 15.1.2

• Paste cu sos de roșii by Sestrjevitovschii Ina on Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Cookies and More by Sarah Shaffer on Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Raspberry waffles by Izabelle Acheson on Unsplash is used under the Unsplash License (https://unsplash.com/license).
• Homemade croissant & pain au chocolat by Cristiano Pinto on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 15.1.3

Inflammed_mucous_layer_of_the_intestinal_villi_depicting_Celiac_disease by www.scientificanimations.com (image 140/191) on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

 

The female sex hormone secreted mainly by the ovaries.

As per caption.

Image shows a diagram labeling the major arteries of the body. Some of these include the carotid artery which provides blood to the neck and head, the brachiocephalic artery which supplies blood to the arms and head, the renal artery supplying blood to the kidneys, the mesenteric arteries supplying blood to the intestines, the femoral arteries supplying blood to the legs.

A testable proposed explanation for a phenomenon.

 

If you’re an ice cream lover, then just the sight of this yummy ice cream cone may make your mouth water. The “water” in your mouth is actually saliva, a fluid released by glands that are part of the digestive system. Saliva contains digestive enzymes, among other substances important for digestion. When your mouth waters at the sight of a tasty treat, it’s a sign that your digestive system is preparing to digest food.

The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Organs of the digestive system are shown in Figure 15.2.2. Most of these organs make up the gastrointestinal (GI) tract, through which food actually passes. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them.

The digestive system has three main functions relating to food: digestion of food, absorption of nutrients from food, and elimination of solid food waste. Digestion is the process of breaking down food into components the body can absorb. It consists of two types of processes: mechanical digestion and chemical digestion. Mechanical digestion is the physical breakdown of chunks of food into smaller pieces, and it takes place mainly in the mouth and stomach. Chemical digestion is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by body fluids (blood or lymph). This type of digestion begins in the mouth and continues in the stomach, but occurs mainly in the small intestine.

After food is digested, the resulting nutrients are absorbed. Absorption is the process in which substances pass into the bloodstream or lymph system to circulate throughout the body. Absorption of nutrients occurs mainly in the small intestine. Any remaining matter from food that is not digested and absorbed passes out of the body through the anus in the process of elimination.

The gastrointestinal (GI) tract is basically a long, continuous tube that connects the mouth with the anus. If it were fully extended, it would be about nine metres long in adults. It includes the mouth, pharynx, esophagus, stomach, and small and large intestines. Food enters the mouth, and then passes through the other organs of the GI tract, where it is digested and/or absorbed. Finally, any remaining food waste leaves the body through the anus at the end of the large intestine. It takes up to 50 hours for food or food waste to make the complete trip through the GI tract.

Tissues of the GI Tract

The walls of the organs of the GI tract consist of four different tissue layers, which are illustrated in Figure 15.2.3: mucosa, submucosa, muscularis externa, and serosa.

1. The mucosa is the innermost layer surrounding the lumen (open space within the organs of the GI tract). This layer consists mainly of epithelium with the capacity to secrete and absorb substances. The epithelium can secret digestive enzymes and mucus, and it can absorb nutrients and water.
2. The submucosa layer consists of connective tissue that contains blood and lymph vessels, as well as nerves. The vessels are needed to absorb and carry away nutrients after food is digested, and nerves help control the muscles of the GI tract organs.
3. The muscularis externa layer contains two types of smooth muscle: longitudinal muscle and circular muscle. Longitudinal muscle runs the length of the GI tract organs, and circular muscle encircles the organs. Both types of muscles contract to keep food moving through the tract by the process of peristalsis, which is described below.
4. The serosa layer is the outermost layer of the walls of GI tract organs. This is a thin layer that consists of connective tissue and separates the organs from surrounding cavities and tissues.

Peristalisis in the GI Tract

The muscles in the walls of GI tract organs enable peristalsis, which is illustrated in Figure 15.2.5. Peristalsis is a continuous sequence of involuntary muscle contraction and relaxation that moves rapidly along an organ like a wave, similar to the way a wave moves through a spring toy. Peristalsis in organs of the GI tract propels food through the tract.

Watch the video "What is peristalsis?" by Mister Science to see peristalsis in action:

https://youtu.be/kVjeNZA5pi4

What is peristalsis?, Mister Science, 2018.

Immune Function of the GI Tract

The GI tract plays an important role in protecting the body from pathogens. The surface area of the GI tract is estimated to be about 32 square metres (105 square feet), or about half the area of a badminton court. This is more than three times the area of the exposed skin of the body, and it provides a lot of area for pathogens to invade the tissues of the body. The innermost mucosal layer of the walls of the GI tract provides a barrier to pathogens so they are less likely to enter the blood or lymph circulations. The mucus produced by the mucosal layer, for example, contains antibodies that mark many pathogenic microorganisms for destruction. Enzymes in some of the secretions of the GI tract also destroy pathogens. In addition, stomach acids have a very low pH that is fatal for many microorganisms that enter the stomach.

Divisions of the GI Tract

The GI tract is often divided into an upper GI tract and a lower GI tract. For medical purposes, the upper GI tract is typically considered to include all the organs from the mouth through the first part of the small intestine, called the duodenum. For our instructional purposes, it makes more sense to include the mouth through the stomach in the upper GI tract, and all of the small intestine — as well as the large intestine — in the lower GI tract.

Upper GI Tract

The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of digestive enzymes and other secretions by salivary glands inside the mouth. The major salivary gland enzyme is amylase. It begins the chemical digestion of carbohydrates by breaking down starches into sugar. The mouth also begins the mechanical digestion of food. When you chew, your teeth break, crush, and grind food into increasingly smaller pieces. Your tongue helps mix the food with saliva and also helps you swallow.

A lump of swallowed food is called a bolus. The bolus passes from the mouth into the pharynx, and from the pharynx into the esophagus. The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other digestive functions. Peristalsis starts at the top of the esophagus when food is swallowed and continues down the esophagus in a single wave, pushing the bolus of food ahead of it.

From the esophagus, food passes into the stomach, where both mechanical and chemical digestion continue. The muscular walls of the stomach churn and mix the food, thus completing mechanical digestion, as well as mixing the food with digestive fluids secreted by the stomach. One of these fluids is hydrochloric acid (HCl). In addition to killing pathogens in food, it gives the stomach the low pH needed by digestive enzymes that work in the stomach. One of these enzymes is pepsin, which chemically digests proteins. The stomach stores the partially digested food until the small intestine is ready to receive it. Food that enters the small intestine from the stomach is in the form of a thick slurry (semi-liquid) called chyme.

Lower GI Tract

The small intestine is a narrow, but very long tubular organ. It may be almost seven metres long in adults. It is the site of most chemical digestion and virtually all absorption of nutrients. Many digestive enzymes are active in the small intestine, some of which are produced by the small intestine itself, and some of which are produced by the pancreas, an accessory organ of the digestive system. Much of the inner lining of the small intestine is covered by tiny finger-like projections called villi, each of which is covered by even tinier projections called microvilli. These projections, shown in the drawing below (Figure 15.2.6), greatly increase the surface area through which nutrients can be absorbed from the small intestine.

From the small intestine, any remaining nutrients and food waste pass into the large intestine. The large intestine is another tubular organ, but it is wider and shorter than the small intestine. It connects the small intestine and the anus. Waste that enters the large intestine is in a liquid state. As it passes through the large intestine, excess water is absorbed from it. The remaining solid waste — called feces — is eventually eliminated from the body through the anus.

Accessory organs of the digestive system are not part of the GI tract, so they are not sites where digestion or absorption take place. Instead, these organs secrete or store substances needed for the chemical digestion of food. The accessory organs include the liver, gallbladder, and pancreas. They are shown in Figure 15.2.7 and described in the text that follows.

• The liver is an organ with multitude of functions. Its main digestive function is producing and secreting a fluid called bile, which reaches the small intestine through a duct. Bile breaks down large globules of lipids into smaller ones that are easier for enzymes to chemically digest. Bile is also needed to reduce the acidity of food entering the small intestine from the highly acidic stomach, because enzymes in the small intestine require a less acidic environment in order to work.
• The gallbladder is a small sac below the liver that stores some of the bile from the liver. The gallbladder also concentrates the bile by removing some of the water from it. It then secretes the concentrated bile into the small intestine as needed for fat digestion following a meal.
• The pancreas secretes many digestive enzymes, and releases them into the small intestine for the chemical digestion of carbohydrates, proteins, and lipids. The pancreas also helps lessen the acidity of the small intestine by secreting bicarbonate, a basic substance that neutralizes acid.

 

Attributions

Figure 15.2.1

Ice Cream [photo] by Mark Cruz on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 15.2.2

Blausen_0316_DigestiveSystem by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 15.2.3

Intestinal_layers by Boumphreyfr on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

Figure 15.2.4

512px-Normal_gastric_mucosa_intermed_mag by Nephron on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

Figure 15.2.5

Peristalsis pushes food through the GI tract by CK-12 Foundation is used under a CC BY NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.

Figure 15.2.6

Villi_&_microvilli_of_small_intestine.svg by BallenaBlanca on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 15.2.7

Blausen_0428_Gallbladder-Liver-Pancreas_Location 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.

Brainard, J/ CK-12 Foundation. (2016). Figure 4 Peristalsis pushes food through the GI tract. [digital image]. In CK-12 College Human Biology (Section 17.2) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/17.2/

Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/channel/UCxTlkZfjArUobBAeVwzJjYg/videos

TED-Ed. (2017, November 13). How does your body know you're full? - Hilary Coller. YouTube. https://www.youtube.com/watch?v=YVfyYrEmzgM&feature=youtu.be

TED-Ed. (2017, December 14). How your digestive system works - Emma Bryce. YouTube. https://www.youtube.com/watch?v=Og5xAdC8EUI&feature=youtu.be

 

 

Created by CK-12 Foundation/Adapted by Christine Miller

If you’re an ice cream lover, then just the sight of this yummy ice cream cone may make your mouth water. The “water” in your mouth is actually saliva, a fluid released by glands that are part of the digestive system. Saliva contains digestive enzymes, among other substances important for digestion. When your mouth waters at the sight of a tasty treat, it’s a sign that your digestive system is preparing to digest food.

The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Organs of the digestive system are shown in Figure 15.2.2. Most of these organs make up the gastrointestinal (GI) tract, through which food actually passes. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them.

The digestive system has three main functions relating to food: digestion of food, absorption of nutrients from food, and elimination of solid food waste. Digestion is the process of breaking down food into components the body can absorb. It consists of two types of processes: mechanical digestion and chemical digestion. Mechanical digestion is the physical breakdown of chunks of food into smaller pieces, and it takes place mainly in the mouth and stomach. Chemical digestion is the chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by body fluids (blood or lymph). This type of digestion begins in the mouth and continues in the stomach, but occurs mainly in the small intestine.

After food is digested, the resulting nutrients are absorbed. Absorption is the process in which substances pass into the bloodstream or lymph system to circulate throughout the body. Absorption of nutrients occurs mainly in the small intestine. Any remaining matter from food that is not digested and absorbed passes out of the body through the anus in the process of elimination.

The gastrointestinal (GI) tract is basically a long, continuous tube that connects the mouth with the anus. If it were fully extended, it would be about nine metres long in adults. It includes the mouth, pharynx, esophagus, stomach, and small and large intestines. Food enters the mouth, and then passes through the other organs of the GI tract, where it is digested and/or absorbed. Finally, any remaining food waste leaves the body through the anus at the end of the large intestine. It takes up to 50 hours for food or food waste to make the complete trip through the GI tract.

Tissues of the GI Tract

The walls of the organs of the GI tract consist of four different tissue layers, which are illustrated in Figure 15.2.3: mucosa, submucosa, muscularis externa, and serosa.

1. The mucosa is the innermost layer surrounding the lumen (open space within the organs of the GI tract). This layer consists mainly of epithelium with the capacity to secrete and absorb substances. The epithelium can secret digestive enzymes and mucus, and it can absorb nutrients and water.
2. The submucosa layer consists of connective tissue that contains blood and lymph vessels, as well as nerves. The vessels are needed to absorb and carry away nutrients after food is digested, and nerves help control the muscles of the GI tract organs.
3. The muscularis externa layer contains two types of smooth muscle: longitudinal muscle and circular muscle. Longitudinal muscle runs the length of the GI tract organs, and circular muscle encircles the organs. Both types of muscles contract to keep food moving through the tract by the process of peristalsis, which is described below.
4. The serosa layer is the outermost layer of the walls of GI tract organs. This is a thin layer that consists of connective tissue and separates the organs from surrounding cavities and tissues.

Peristalisis in the GI Tract

The muscles in the walls of GI tract organs enable peristalsis, which is illustrated in Figure 15.2.5. Peristalsis is a continuous sequence of involuntary muscle contraction and relaxation that moves rapidly along an organ like a wave, similar to the way a wave moves through a spring toy. Peristalsis in organs of the GI tract propels food through the tract.

Watch the video "What is peristalsis?" by Mister Science to see peristalsis in action:

https://youtu.be/kVjeNZA5pi4

What is peristalsis?, Mister Science, 2018.

Immune Function of the GI Tract

The GI tract plays an important role in protecting the body from pathogens. The surface area of the GI tract is estimated to be about 32 square metres (105 square feet), or about half the area of a badminton court. This is more than three times the area of the exposed skin of the body, and it provides a lot of area for pathogens to invade the tissues of the body. The innermost mucosal layer of the walls of the GI tract provides a barrier to pathogens so they are less likely to enter the blood or lymph circulations. The mucus produced by the mucosal layer, for example, contains antibodies that mark many pathogenic microorganisms for destruction. Enzymes in some of the secretions of the GI tract also destroy pathogens. In addition, stomach acids have a very low pH that is fatal for many microorganisms that enter the stomach.

Divisions of the GI Tract

The GI tract is often divided into an upper GI tract and a lower GI tract. For medical purposes, the upper GI tract is typically considered to include all the organs from the mouth through the first part of the small intestine, called the duodenum. For our instructional purposes, it makes more sense to include the mouth through the stomach in the upper GI tract, and all of the small intestine — as well as the large intestine — in the lower GI tract.

Upper GI Tract

The mouth is the first digestive organ that food enters. The sight, smell, or taste of food stimulates the release of digestive enzymes and other secretions by salivary glands inside the mouth. The major salivary gland enzyme is amylase. It begins the chemical digestion of carbohydrates by breaking down starchesno post into sugar. The mouth also begins the mechanical digestion of food. When you chew, your teeth break, crush, and grind food into increasingly smaller pieces. Your tongue helps mix the food with saliva and also helps you swallow.

A lump of swallowed food is called a bolus. The bolus passes from the mouth into the pharynx, and from the pharynx into the esophagus. The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other digestive functions. Peristalsis starts at the top of the esophagus when food is swallowed and continues down the esophagus in a single wave, pushing the bolus of food ahead of it.

From the esophagus, food passes into the stomach, where both mechanical and chemical digestion continue. The muscular walls of the stomach churn and mix the food, thus completing mechanical digestion, as well as mixing the food with digestive fluids secreted by the stomach. One of these fluids is hydrochloric acid (HCl). In addition to killing pathogens in food, it gives the stomach the low pH needed by digestive enzymes that work in the stomach. One of these enzymes is pepsin, which chemically digests proteins. The stomach stores the partially digested food until the small intestine is ready to receive it. Food that enters the small intestine from the stomach is in the form of a thick slurry (semi-liquid) called chyme.

Lower GI Tract

The small intestine is a narrow, but very long tubular organ. It may be almost seven metres long in adults. It is the site of most chemical digestion and virtually all absorption of nutrients. Many digestive enzymes are active in the small intestine, some of which are produced by the small intestine itself, and some of which are produced by the pancreas, an accessory organ of the digestive system. Much of the inner lining of the small intestine is covered by tiny finger-like projections called villi, each of which is covered by even tinier projections called microvilli. These projections, shown in the drawing below (Figure 15.2.6), greatly increase the surface area through which nutrients can be absorbed from the small intestine.

From the small intestine, any remaining nutrients and food waste pass into the large intestine. The large intestine is another tubular organ, but it is wider and shorter than the small intestine. It connects the small intestine and the anus. Waste that enters the large intestine is in a liquid state. As it passes through the large intestine, excess water is absorbed from it. The remaining solid waste — called feces — is eventually eliminated from the body through the anus.

Accessory organs of the digestive system are not part of the GI tract, so they are not sites where digestion or absorption take place. Instead, these organs secrete or store substances needed for the chemical digestion of food. The accessory organs include the liver, gallbladder, and pancreas. They are shown in Figure 15.2.7 and described in the text that follows.

• The liver is an organ with multitude of functions. Its main digestive function is producing and secreting a fluid called bile, which reaches the small intestine through a duct. Bile breaks down large globules of lipids into smaller ones that are easier for enzymes to chemically digest. Bile is also needed to reduce the acidity of food entering the small intestine from the highly acidic stomach, because enzymes in the small intestine require a less acidic environment in order to work.
• The gallbladder is a small sac below the liver that stores some of the bile from the liver. The gallbladder also concentrates the bile by removing some of the water from it. It then secretes the concentrated bile into the small intestine as needed for fat digestion following a meal.
• The pancreas secretes many digestive enzymes, and releases them into the small intestine for the chemical digestion of carbohydrates, proteins, and lipids. The pancreas also helps lessen the acidity of the small intestine by secreting bicarbonate, a basic substance that neutralizes acid.

 

Attributions

Figure 15.2.1

Ice Cream [photo] by Mark Cruz on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 15.2.2

Blausen_0316_DigestiveSystem by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 15.2.3

Intestinal_layers by Boumphreyfr on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

Figure 15.2.4

512px-Normal_gastric_mucosa_intermed_mag by Nephron on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license.

Figure 15.2.5

Peristalsis pushes food through the GI tract by CK-12 Foundation is used under a CC BY NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license.

Figure 15.2.6

Villi_&_microvilli_of_small_intestine.svg by BallenaBlanca on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 15.2.7

Blausen_0428_Gallbladder-Liver-Pancreas_Location 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.

Brainard, J/ CK-12 Foundation. (2016). Figure 4 Peristalsis pushes food through the GI tract. [digital image]. In CK-12 College Human Biology (Section 17.2) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-college-human-biology/section/17.2/

Mister Science. (2018). What is peristalsis? YouTube. https://www.youtube.com/channel/UCxTlkZfjArUobBAeVwzJjYg/videos

TED-Ed. (2017, November 13). How does your body know you're full? - Hilary Coller. YouTube. https://www.youtube.com/watch?v=YVfyYrEmzgM&feature=youtu.be

TED-Ed. (2017, December 14). How your digestive system works - Emma Bryce. YouTube. https://www.youtube.com/watch?v=Og5xAdC8EUI&feature=youtu.be

 

 

Image shows a man participating in a hot-dog eating contest. His mouth is so full of hot dog that he can't close his lips.

Image shows a side view diagram of the male and female pelvis. The male urethra is much longer because it extends through the penis, and in women it exits through the pelvic floor.

A biological process which converts sugars such as glucose, fructose, and sucrose into cellular energy, producing ethanol and carbon dioxide as by-products.

Created by CK-12 Foundation/Adapted by Christine Miller

Case Study Conclusion: Cough That Won't Quit

Inhaling the moist air from a humidifier or steamy shower can feel particularly good if you have a respiratory system infection, such as bronchitis. The moist air helps to loosen and thin mucus in the respiratory system, allowing you to breathe easier.

In the beginning of this chapter, you learned about Erica, who developed acute bronchitis after getting a cold. She had a worsening cough, a sore throat due to coughing, and chest congestion. She was also coughing up thick mucus.

Acute bronchitis usually occurs after a cold or flu, usually due to the same viruses that cause cold or flu. Because bronchitis is not usually caused by bacteria (although it can be), in most cases, antibiotics are not an effective treatment.

Bronchitis affects the bronchial tubes, which, as you have learned, are air passages in the lower respiratory tract. The main bronchi branch off of the trachea and then branch into smaller bronchi, and then bronchioles. In bronchitis, the walls of the bronchi become inflamed, which makes them narrower. There is also excessive production of mucus in the bronchi, which further narrows the pathway where air can flow through. Figure 13.7.2, shows how bronchitis affects the bronchial tubes.

The treatment for most cases of bronchitis involves thinning and loosening the mucus so that it can be effectively coughed out of the airways. This can be done by drinking plenty of fluids, using humidifiers or steam, and — in some cases — using over-the-counter medications (such as expectorants). Dr. Choo recommended some of these treatments to Erica, and also warned against using cough suppressants. Cough suppressants work on the nervous system to suppress the cough reflex. When a patient has a “productive” cough (which means they are coughing up mucus), doctors generally advise them not to take cough suppressants, so that they can cough the mucus out of their bodies.

When Dr. Choo was examining Erica, she used a pulse oximeter to measure the oxygen level in her blood. Why did she do this? As you have learned, the bronchial tubes branch into bronchioles, which ultimately branch into the alveoli of the lungs. The alveoli are where gas exchange occurs between the air and the blood to take in oxygen and remove carbon dioxide and other wastes. By checking Erica’s blood oxygen level, Dr. Choo was making sure that her clogged airways were not impacting her level of much-needed oxygen.

Erica has acute bronchitis, but you may recall that chronic bronchitis was discussed earlier in this chapter (Section 13.5) as a term that describes the symptoms of chronic obstructive pulmonary disease (COPD). COPD is often due to tobacco smoking, and it causes damage to the walls of the alveoli. Acute bronchitis, on the other hand, typically occurs after a cold or flu, and involves inflammation and mucus build-up in the bronchial tubes. As implied by the difference in their names, chronic bronchitis is an ongoing, long-term condition, while acute bronchitis is likely to resolve relatively quickly with proper rest and treatment.

Erica uses e-cigarettes (vaping), so she is more likely to develop chronic respiratory conditions, such as COPD. As you have learned, smoking damages the respiratory system, along with many other systems of the body. Smoking and vaping increases the risk of respiratory infections, including bronchitis and flu, due to its damaging effects on the respiratory and immune systems. Dr. Choo strongly encouraged Erica to quit vaping, not only so that her acute bronchitis resolves, but so that she can avoid future infections and other negative health outcomes associated with vaping and smoking, including COPD and lung cancer.

As you have learned in this chapter, the respiratory system is critical to carry out the gas exchange necessary for life’s functions, and to protect the body from pathogens and other potentially harmful substances in the air. But this ability to interface with the outside air has a cost. The respiratory system is prone to infections, as well as damage and other negative effects from allergens, mold, air pollution, cigarette smoke and vaping. While exposure to most of these things cannot be avoided, not smoking is an important step you can take to protect this organ system — as well as many other systems of your body.

Attributions

Figure 13.7.1

Tags: Essential Oils Aroma Diffuser Diffuse Led by asundermeier on Pixabay is used under the Pixabay License (https://unsplash.com/license).

Figure 13.7.2

Bronchitis by National Heart Lung and Blood Institute on Wikimedia Commons is in the public domain (https://en.wikipedia.org/wiki/Public_domain).

 

The space occurring between two or more membranes. In cell biology, it's most commonly described as the region between the inner membrane and the outer membrane of a mitochondrion or a chloroplast.

Any type of a close and long-term biological interaction between two different biological organisms.

Created by CK-12 Foundation/Adapted by Christine Miller

Nineteen-year-old Malcolm is about to take his first plane flight. Shortly after he boards the plane and sits down, a man in his late sixties sits next to him in the aisle seat. About half an hour after the plane takes off, the pilot announces that she is turning the seat belt light off, and that it is safe to move around the cabin.

The man in the aisle seat — who has introduced himself to Malcolm as Willie — immediately unbuckles his seat belt and paces up and down the aisle a few times before returning to his seat. After about 45 minutes, Willie gets up again, walks some more, then sits back down and does some foot and leg exercises. After the third time Willie gets up and paces the aisles, Malcolm asks him whether he is walking so much to accumulate steps on a pedometer or fitness tracking device. Willie laughs and says no. He is actually trying to do something even more important for his health — prevent a blood clot from forming in his legs.

Willie explains that he has a chronic condition: heart failure. Although it sounds scary, his condition is currently well-managed, and he is able to lead a relatively normal lifestyle. However, it does put him at risk of developing other serious health conditions, such as deep vein thrombosis (DVT), which is when a blood clot occurs in the deep veins, usually in the legs. Air travel — and other situations where a person has to sit for a long period of time — increases the risk of DVT. Willie’s doctor said that he is healthy enough to fly, but that he should walk frequently and do leg exercises to help avoid a blood clot.

As you read this chapter, you will learn about the heart, blood vessels, and blood that make up the cardiovascular system, as well as disorders of the cardiovascular system, such as heart failure. At the end of the chapter you will learn more about why DVT occurs, why Willie has to take extra precautions when he flies, and what can be done to lower the risk of DVT and its potentially deadly consequences.

Attribution

Figure 14.1.1

aircraft-1583871_1920 [photo] by olivier89 from Pixabay is used under the Pixabay License (https://pixabay.com/de/service/license/).

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 cells. But what are skin cells made of? Like all living cells, they are made of matter. In fact, all things are made of matter. Matter is anything that takes up space and has mass. Matter, in turn, is made up of chemical substances. A chemical substance 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 element is a pure substance. It cannot be broken down into other types of substances. Each element is made up of just one type of atom.

Structure of an Atom

An atom 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.

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 ion.

The negatively-charged electrons of an atom are attracted to the positively-charged protons in the nucleus by a force called electromagnetic force, 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 nuclear force, 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.

A compound 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 molecule.

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 chemical bond 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 chemical reaction 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.

 

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 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.

An organisms that is so small it is invisible to the human eye.

Image shows a diagram comparing a healthy nephron and its blood supply and one with diabetic nephropathy. The diseased one has blood vessels that look deformed and fragile.

Image shows a diagram of the process of hemodialysis. Blood is removed from the patient from a location on the arm. Blood enters the hemodialysis apparatus and is run through dialyser to clean wastes from the blood. There are mechanisms to maintain blood tonicity and pressure, to prevent clotting, and ensure no air enters the bloodstream. The cleaned blood is returned to the patient in their arm, proximal to the place where the blood was first removed.

Image shows a photograph of a kidney stone. It has a crystal structure, with irregular sharp edges and points.

Image shows a diagram of the kidney with several kidney stones, which have accumulated in the renal pelvis and are blocking the exit to the ureter.

As per caption

Image shows a photograph of several wine bottles on a shelf. The image has been deliberately blurred to simulate the effects of drunkeness.

Image shows an operating room. There are several surgeons in gowns, masks and gloves. They are operating on a patient.

A semi-permeable lipid bilayer that separates the interior of all cells from their surroundings.

Created by CK-12 Foundation/Adapted by Christine Miller

Imagine the man in Figure 12.3.1 turns his eyes in your direction. This is a very small movement, considering the conspicuously large and strong external eye muscles that control eyeball movements. These muscles have been called the strongest muscles in the human body relative to the work they do. However, the external eye muscles actually do a surprising amount of work. Eye movements occur almost constantly during waking hours, especially when we are scanning faces or reading. Eye muscles are also exercised nightly during the phase of sleep called rapid eye movement sleep. External eye muscles can move the eyes because they are made mainly of muscle tissue.

Muscle tissue is a soft tissue that makes up most of the tissues in the muscles of the human muscular system. Other tissues in muscles are connective tissues, such as tendons that attach skeletal muscles to bones and sheaths of connective tissues that cover or line muscle tissues. Only muscle tissue per se, has cells with the ability to contract.

There are three major types of muscle tissues in the human body: skeletal, smooth, and cardiac muscle tissues. Figure 12.3.2 shows how the three types of muscle tissues appear under magnification. When you read about each type below, you will learn why the three types appear as they do.

Skeletal muscle is muscle tissue that is attached to bones by tendons, which are bundles of collagen fibres. Whether you are moving your eyes or running a marathon, you are using skeletal muscles. Contractions of skeletal muscles are voluntary, or under conscious control of the central nervous system via the somatic nervous system. Skeletal muscle tissue is the most common type of muscle tissue in the human body. By weight, an average adult male is about 42% skeletal muscles, and the average adult female is about 36% skeletal muscles. Some of the major skeletal muscles in the human body are labeled in Figure 12.3.3 below.

Skeletal Muscle Pairs

To move bones in opposite directions, skeletal muscles often consist of muscle pairs that work in opposition to one another, also called antagonistic muscle pairs.  For example, when the biceps muscle (on the front of the upper arm) contracts, it can cause the elbow joint to flex or bend the arm, as shown in Figure 12.3.4. When the triceps muscle (on the back of the upper arm) contracts, it can cause the elbow to extend or straighten the arm. The biceps and triceps muscles, also shown in Figure 12.3.4, are an example of a muscle pair where the muscles work in opposition to each other.

Skeletal Muscle Structure

Each skeletal muscle consists of hundreds — or even thousands — of skeletal muscle fibres, which are long, string-like cells. As shown in Figure 12.3.5 below, skeletal muscle fibres are individually wrapped in connective tissue called endomysium. The skeletal muscle fibres are bundled together in units called muscle fascicles, which are surrounded by sheaths of connective tissue called perimysium. Each fascicle contains between ten and 100 (or even more!) skeletal muscle fibres. Fascicles, in turn, are bundled together to form individual skeletal muscles, which are wrapped in connective tissue called epimysium. The connective tissues in skeletal muscles have a variety of functions. They support and protect muscle fibres, allowing them to withstand the forces of contraction by distributing the forces applied to the muscle. They also provide pathways for nerves and blood vessels to reach the muscles. In addition, the epimysium anchors the muscles to tendons.

The same bundles-within-bundles structure is replicated within each muscle fibre. As shown in Figure 12.3.6, a muscle fibre consists of a bundle of myofibrils, which are themselves bundles of protein filaments. These protein filaments consist of thin filaments of the protein actin, which are anchored to structures called Z discs, and thick filaments of the protein myosin. The filaments are arranged together within a myofibril in repeating units called sarcomeres, which run from one Z disc to the next. The sarcomere is the basic functional unit of skeletal and cardiac muscles. It contracts as actin and myosin filaments slide over one another. Skeletal muscle tissue is said to be striated, because it appears striped. It has this appearance because of the regular, alternating A (dark) and I (light) bands of filaments arranged in sarcomeres inside the muscle fibres. Other components of a skeletal muscle fibre include multiple nuclei and mitochondria.

Slow- and Fast-Twitch Skeletal Muscle Fibres

Skeletal muscle fibres can be divided into two types, called slow-twitch (or type I) muscle fibres and fast-twitch (or type II) muscle fibres.

• Slow-twitch muscle fibres are dense with capillaries and rich in mitochondria and myoglobin, which is a protein that stores oxygen until needed for muscle activity. Relative to fast-twitch fibres, slow-twitch fibres can carry more oxygen and sustain aerobic (oxygen-using) activity. Slow-twitch fibres can contract for long periods of time, but not with very much force. They are relied upon primarily in endurance events, such as distance running or cycling.
• Fast-twitch muscle fibres contain fewer capillaries and mitochondria and less myoglobin. This type of muscle fibre can contract rapidly and powerfully, but it fatigues very quickly. Fast-twitch fibres can sustain only short, anaerobic (non-oxygen-using) bursts of activity. Relative to slow-twitch fibres, fast-twitch fibres contribute more to muscle strength and have a greater potential for increasing in mass. They are relied upon primarily in short, strenuous events, such as sprinting or weightlifting.

Proportions of fibre types vary considerably from muscle to muscle and from person to person. Individuals may be genetically predisposed to have a larger percentage of one type of muscle fibre than the other. Generally, an individual who has more slow-twitch fibres is better suited for activities requiring endurance, whereas an individual who has more fast-twitch fibres is better suited for activities requiring short bursts of power.

Smooth muscle is muscle tissue in the walls of internal organs and other internal structures such as blood vessels. When smooth muscles contract, they help the organs and vessels carry out their functions. When smooth muscles in the stomach wall contract, for example, they squeeze the food inside the stomach, helping to mix and churn the food and break it into smaller pieces. This is an important part of digestion. Contractions of smooth muscles are involuntary, so they are not under conscious control. Instead, they are controlled by the autonomic nervous system, hormones, neurotransmitters, and other physiological factors.

Structure of Smooth Muscle

The cells that make up smooth muscle are generally called myocytes. Unlike the muscle fibres of striated muscle tissue, the myocytes of smooth muscle tissue do not have their filaments arranged in sarcomeres. Therefore, smooth tissue is not striated. However, the myocytes of smooth muscle do contain myofibrils, which in turn contain bundles of myosin and actin filaments. The filaments cause contractions when they slide over each other, as shown in Figure 12.3.7.

Unlike striated muscle, smooth muscle can sustain very long-term contractions. Smooth muscle can also stretch and still maintain its contractile function, which striated muscle cannot. The elasticity of smooth muscle is enhanced by an extracellular matrix secreted by myocytes. The matrix consists of elastin, collagen, and other stretchy fibres. The ability to stretch and still contract is an important attribute of smooth muscle in organs such as the stomach and uterus (see Figures 12.3.8 and 12.3.9), both of which must stretch considerably as they perform their normal functions.

The following list indicates where many smooth muscles are found, along with some of their specific functions.

• Walls of organs of the gastrointestinal tract (such as the esophagus, stomach, and intestines), moving food through the tract by peristalsis
• Walls of air passages of the respiratory tract (such as the bronchi), controlling the diameter of the passages and the volume of air that can pass through them
• Walls of organs of the male and female reproductive tracts; in the uterus, for example, pushing a baby out of the uterus and into the birth canal
• Walls of structures of the urinary system, including the urinary bladder, allowing the bladder to expand so it can hold more urine, and then contract as urine is released
• Walls of blood vessels, controlling the diameter of the vessels and thereby affecting blood flow and blood pressure
• Walls of lymphatic vessels, squeezing the fluid called lymph through the vessels
• Iris of the eyes, controlling the size of the pupils and thereby the amount of light entering the eyes
• Arrector pili in the skin, raising hairs in hair follicles in the dermis

Cardiac muscle is found only in the wall of the heart. It is also called myocardium. As shown in Figure 12.3.10, myocardium is enclosed within connective tissues, including the endocardium on the inside of the heart and pericardium on the outside of the heart. When cardiac muscle contracts, the heart beats and pumps blood. Contractions of cardiac muscle are involuntary, like those of smooth muscles. They are controlled by electrical impulses from specialized cardiac muscle cells in an area of the heart muscle called the sinoatrial node.

Like skeletal muscle, cardiac muscle is striated because its filaments are arranged in sarcomeres inside the muscle fibres. However, in cardiac muscle, the myofibrils are branched at irregular angles rather than arranged in parallel rows (as they are in skeletal muscle). This explains why cardiac and skeletal muscle tissues look different from one another.

The cells of cardiac muscle tissue are arranged in interconnected networks. This arrangement allows rapid transmission of electrical impulses, which stimulate virtually simultaneous contractions of the cells. This enables the cells to coordinate contractions of the heart muscle.

The heart is the muscle that performs the greatest amount of physical work in the course of a lifetime. Although the power output of the heart is much less than the maximum power output of some other muscles in the human body, the heart does its work continuously over an entire lifetime without rest. Cardiac muscle contains a great many mitochondria, which produce ATP for energy and help the heart resist fatigue.

Cardiomyopathy is a disease in which the muscles of the heart are no longer able to effectively pump blood to the body — extreme forms of this disease can lead to heart failure.  There are four main types of cardiomyopathy (also illustrated in Figure 12.3.11):

• Dilated (congestive) cardiomyopathy: the left ventricle (the chamber itself) of the heart becomes enlarged and can't pump blood our to the body.  This is normally related to coronary artery disease and/or heart attack
• Hypertrophic cardiomyopathy: abnormal thickening of the muscular walls of the left ventricle make the chamber less able to work properly.  This condition is more common in patients with a family history of the disease.
• Restrictive cardiomyopathy: the myocardium becomes abnormally rigid and inelastic and is unable to expand in between heartbeats to refill with blood.  Restrictive cardiomyopathy typically affects older people.
• Arrhythmogenic right ventricular cardiomyopathy: the right ventricular muscle is replaced by adipose or scar tissue, reducing elasticity and interfering with normal heartbeat and rhythm.  This disease is often caused by genetic mutations.

Cardiomyopathy is typically diagnosed with a physical exam supplemented by medical and family history, an angiogram, blood tests, chest x-rays and electrocardiograms.  In some cases your doctor would also requisition a CT scan and/or genetic testing.

When treating cardiomyopathy, the goal is to reduce symptoms that affect everyday life.  Certain medications can help regularize and slow heart rate, decrease chances of blood clots and cause vasodilation in the coronary arteries.  If medication is not sufficient to manage symptoms, a pacemaker or even a heart transplant may be the best option.  Lifestyle can also help manage the symptoms of cardiomyopathy — people living with this disease are encouraged to avoid drug and alcohol use, control high blood pressure, eat a healthy diet, get ample rest and exercise, as well as reduce stress levels.

 

Attributions

Figure 12.3.1

Look by ali-yahya-155huuQwGvA [photo] by Ali Yahya on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 12.3.2

Skeletal_Smooth_Cardiac by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 12.3.3

Anterior_and_Posterior_Views_of_Muscles by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.

Figure 12.3.4

Antagonistic Muscle Pair by Laura Guerin at CK-12 Foundation on Wikimedia Commons is used under a CC BY-NC 3.0 (https://creativecommons.org/licenses/by-nc/3.0/) license. 

Figure 12.3.5

Muscle_Fibes_(large) by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.

Figure 12.3.6

Muscle_Fibers_(small) by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.

Figure 12.3.7

Smooth_Muscle_Contraction by OpenStax on Wikimedia Commons is used under a CC BY 4.0 (https://creativecommons.org/licenses/by/4.0) license.

Figure 12.3.8

Blausen_0747_Pregnancy by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 12.3.9

Size_of_Uterus_Throughout_Pregnancy-02 by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 12.3.10

1024px-Blausen_0470_HeartWall by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 12.3.11

Tipet_e_kardiomiopative by Npatchett at English Wikipedia on Wikimedia Commons is used under a CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) license. (Work derived from Blausen 0165 Cardiomyopathy Dilated by BruceBlaus)

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 4.18 Muscle tissue [digital image].  In Anatomy and Physiology (Section 4.4). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/4-4-muscle-tissue-and-motion

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 28.18 Size of uterus throughout pregnancy [digital image].  In Anatomy and Physiology (Section 28.4). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/28-4-maternal-changes-during-pregnancy-labor-and-birth

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 10.3 The three connective tissue layers [digital image].  In Anatomy and Physiology (Section 10.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-2-skeletal-muscle

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 10.4 Muscle fiber [digital image].  In Anatomy and Physiology (Section 10.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-2-skeletal-muscle

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 10.24 Muscle contraction [digital image].  In Anatomy and Physiology (Section 10.8). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/10-8-smooth-muscle

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 11.5 Overview of the muscular system [digital image].  In Anatomy and Physiology (Section 11.2). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/11-2-naming-skeletal-muscles

Blausen.com staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Brainard, J/ CK-12 Foundation. (2012). Figure 5 Triceps and biceps muscles in the upper arm are opposing muscles. [digital image]. In CK-12 Biology (Section 21.3) [online Flexbook]. CK12.org. https://www.ck12.org/book/ck-12-biology/section/21.3/ (Last modified August 11, 2017.)

khanacademymedicine. (2012, October 19). Three types of muscle | Circulatory system physiology | NCLEX-RN | Khan Academy. YouTube.

TED-Ed. (2017, February 14).  What happens during a heart attack? - Krishna Sudhir. YouTube. https://www.youtube.com/watch?v=3_PYnWVoUzM&feature=youtu.be

Created by CK-12/Adapted by Christine Miller

As you read in the beginning of this chapter, new parents Samantha and Aki left their pediatrician’s office still unsure whether or not to vaccinate baby James. Dr. Rodriguez gave them a list of reputable sources where they could look up information about the safety of vaccines, including the Centers for Disease Control and Prevention (CDC). Samantha and Aki read that the consensus within the scientific community is that there is no link between vaccines and autism. They find a long list of studies published in peer-reviewed scientific journals that disprove any link. Additionally, some of the studies are “meta-analyses” that analyzed the findings from many individual studies. The new parents are reassured by the fact that many different researchers, using a large number of subjects in numerous well-controlled and well-reviewed studies, all came to the same conclusion.

Samantha also went back to the web page that originally scared her about the safety of vaccines. She found that the author was not a medical doctor or scientific researcher, but rather a self-proclaimed “child wellness expert.” He sold books and advertising on his site, some of which were related to claims of vaccine injury. She realized that he was both an unqualified and potentially biased source of information.

Samantha also realized that some of his arguments were based on correlations between autism and vaccines, but, as the saying goes, “correlation does not imply causation.” For instance, the recent rise in autism rates may have occurred during the same time period as an increase in the number of vaccines given in childhood, but Samantha could think of many other environmental and social factors that have also changed during this time period. There are just too many variables to come to the conclusion that vaccines, or anything else, are the cause of the rise in autism rates based on that type of argument alone. Also, she learned that the age of onset of autism symptoms happens to typically be around the time that the MMR vaccine is first given, so the apparent association in the timing may just be a coincidence.

Finally, Samantha came across news about  a measles outbreak in Vancouver, British Columbia in the winter of 2019. Measles wasn’t just a disease of the past! She learned that measles and whooping cough, which had previously been rare thanks to widespread vaccinations, are now on the rise, and that people choosing not to vaccinate their children seems to be one of the contributing factors. She realized that it is important to vaccinate her baby against these diseases, not only to protect him from their potentially deadly effects, but also to protect others in the population.

In their reading, Samantha and Aki learn that scientists do not yet know the causes of autism, but they feels reassured by the abundance of data that disproves any link with vaccines. Both parents think that the potential benefits of protecting their baby’s health against deadly diseases outweighs any unsubstantiated claims about vaccines. They will be making an appointment to get baby James his shots soon.

Attribution

Figure 1.8.1

[Photo of person sitting in front of personal computer] by Avel Chuklanov on Unsplash is used under the Unsplash License (https://unsplash.com/license).

a hormonal disorder common among women of reproductive age. Women with PCOS may have infrequent or prolonged menstrual periods or excess male hormone (androgen) levels. The ovaries may develop numerous small collections of fluid (follicles) and fail to regularly release eggs.

A type of disease in which cells of the central nervous system stop working or die. Neurodegenerative disorders usually get worse over time and have no cure. They may be genetic or be caused by a tumor or stroke.

A mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.

A hormone is a signaling molecule produced by glands in multicellular organisms that target distant organs to regulate physiology and behavior.

 

 

Lub dub, lub dub, lub dub... That’s how the sound of a beating heart is typically described. Those are also the only two sounds that should be audible when listening to a normal, healthy heart through a stethoscope, as in Figure 14.3.1.  If a doctor hears something different from the normal lub dub sounds, it’s a sign of a possible heart abnormality. What causes the heart to produce the characteristic lub dub sounds? Read on to find out.

The heart is a muscular organ behind the sternum (breastbone), slightly to the left of the center of the chest. A normal adult heart is about the size of a fist. The function of the heart is to pump blood through blood vessels of the cardiovascular system. The continuous flow of blood through the system is necessary to provide all the cells of the body with oxygen and nutrients, and to remove their metabolic wastes.

The heart has a thick muscular wall that consists of several layers of tissue. Internally, the heart is divided into four chambers through which blood flows. Because of heart valves, blood flows in just one direction through the chambers.

Heart Wall

As shown in Figure 14.3.2, the wall of the heart is made up of three layers, called the endocardium, myocardium, and pericardium.

• The endocardium is the innermost layer of the heart wall. It is made up primarily of simple epithelial cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.
• The myocardium is the middle and thickest layer of the heart wall. It consists of cardiac muscle surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes — which have the ability to contract easily — and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.
• The pericardium is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.

Heart Chambers

As shown in Figure 14.3.3 the four chambers of the heart include two upper chambers called atria (singular, atrium), and two lower chambers called ventricles. The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives deoxygenated blood from the upper and lower body through the superior vena cava and inferior vena cava, respectively. The left atrium receives oxygenated blood from the lungs through the pulmonary veins. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the pulmonary artery, and the left ventricle discharges blood to the rest of the body through the aorta. The four chambers are separated from each other by dense connective tissue consisting mainly of collagen.

Heart Valves

Figure 14.3.4 shows the location of the heart's four valves in a top-down view, looking down at the heart as if the arteries and veins feeding into and out of the heart were removed. The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. Figure 14.3.5 shows how valves open to let blood into the appropriate chamber, and then close to prevent blood from moving in the wrong direction and the next chamber contracts.  The four valves are the:

1. Tricuspid atrioventricular valve, (can be shortened to tricuspid AV valve) which allows blood to flow from the right atrium to the right ventricle.
2. Bicuspid atrioventricular valve (also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.
3. Pulmonary semilunar valve, which allows blood to flow from the right ventricle to the pulmonary artery.
4. Aortic semilunar valve, which allows blood to flow from the left ventricle to the aorta.

The cardiomyocytes of the muscular walls of the heart are very active cells, because they are responsible for the constant beating of the heart. These cells need a continuous supply of oxygen and nutrients. The carbon dioxide and waste products they produce also must be continuously removed. The blood vessels that carry blood to and from the heart muscle cells make up the coronary circulation. Note that the blood vessels of the coronary circulation supply heart tissues with blood, and are different from the blood vessels that carry blood to and from the chambers of the heart as part of the general circulation. Coronary arteries supply oxygen-rich blood to the heart muscle cells. Coronary veins remove deoxygenated blood from the heart muscles cells.

• There are two coronary arteries — a right coronary artery that supplies the right side of the heart, and a left coronary artery that supplies the left side of the heart. These arteries branch repeatedly into smaller and smaller arteries and finally into capillaries, which exchange gases, nutrients, and waste products with cardiomyocytes.
• At the back of the heart, small cardiac veins drain into larger veins, and finally into the great cardiac vein, which empties into the right atrium. At the front of the heart, small cardiac veins drain directly into the right atrium.

Figure 14.3.7 shows how blood circulates through the chambers of the heart. The right atrium collects blood from two large veins, the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The blood that collects in the right atrium is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it enters the pulmonary circulation, gives up carbon dioxide, and picks up oxygen. The oxygenated blood travels back from the lungs through the pulmonary veins (of which there are four), and enters the left atrium of the heart. From the left atrium, the blood is pumped through the mitral valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta, which subsequently branches into smaller arteries that carry the blood throughout the rest of the body. After passing through capillaries and exchanging substances with cells, the blood returns to the right atrium via the superior vena cava and inferior vena cava, and the process begins anew.

The cardiac cycle refers to a single complete heartbeat, which includes one iteration of the lub and dub sounds heard through a stethoscope. During the cardiac cycle, the atria and ventricles work in a coordinated fashion so that blood is pumped efficiently through and out of the heart. The cardiac cycle includes two parts, called diastole and systole, which are illustrated in the diagrams in Figure 14.3.8.

• During diastole, the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.
• During systole, the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.

Electrical Stimulation of the Heart

The normal, rhythmical beating of the heart is called sinus rhythm. It is established by the heart’s pacemaker cells, which are located in an area of the heart called the sinoatrial node (shown in Figure 14.3.9). The pacemaker cells create electrical signals with the movement of electrolytes (sodium, potassium, and calcium ions) into and out of the cells. For each cardiac cycle, an electrical signal rapidly travels first from the sinoatrial node, to the right and left atria so they contract together. Then, the signal travels to another node, called the atrioventricular node (Figure 14.3.9), and from there to the right and left ventricles (which also contract together), just a split second after the atria contract.

The normal sinus rhythm of the heart is influenced by the autonomic nervous system through sympathetic and parasympathetic nerves. These nerves arise from two paired cardiovascular centers in the medulla of the brainstem. The parasympathetic nerves act to decrease the heart rate, and the sympathetic nerves act to increase the heart rate. Parasympathetic input normally predominates. Without it, the pacemaker cells of the heart would generate a resting heart rate of about 100 beats per minute, instead of a normal resting heart rate of about 72 beats per minute. The cardiovascular centers receive input from receptors throughout the body, and act through the sympathetic nerves to increase the heart rate, as needed. Increased physical activity, for example, is detected by receptors in muscles, joints, and tendons. These receptors send nerve impulses to the cardiovascular centers, causing sympathetic nerves to increase the heart rate, and allowing more blood to flow to the muscles.

Besides the autonomic nervous system, other factors can also affect the heart rate. For example, thyroid hormones and adrenal hormones (such as epinephrine) can stimulate the heart to beat faster. The heart rate also increases when blood pressure drops or the body is dehydrated or overheated. On the other hand, cooling of the body and relaxation — among other factors — can contribute to a decrease in the heart rate.

When a patient’s heart is too diseased or damaged to sustain life, a heart transplant is likely to be the only long-term solution. The first successful heart transplant was undertaken in South Africa in 1967. There are over 2,200 Canadians walking around today because of life-saving heart transplant surgery.  Approximately 180 heart transplant surgeries are performed each year, but there are still so many Canadians on the transplant list that some die while waiting for a heart. The problem is that far too few hearts are available for transplant — there is more demand (people waiting for a heart transplant) than supply (organ donors). Sometimes, recipient hopefuls will receive a device called a Total Artificial Heart (see Figure 14.3.10), which can buy them some time until a donor heart becomes available.

Watch the video below "Total artificial heart option..." from Stanford Health Care to see how it works:

https://youtu.be/1PtxaxcPnGc

Total artificial heart option at Stanford (Includes surgical graphic footage), Stanford Health Care, 2014.

Attributions

Figure 14.3.1

• Female clinician dressed in scrubs using a stethoscope by Amanda Mills, USCDCP, on Pixnio is used under a CC0 public domain certification license (https://creativecommons.org/licenses/publicdomain/).
• Human heart beating loud and strong (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 14.3.2

Blausen_0470_HeartWall by BruceBlaus on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 14.3.3

Diagram_of_the_human_heart_(cropped).svg by Wapcaplet on Wikimedia Commons is used under a CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/) license.

Figure 14.3.4

Heart_Valves by OpenStax College on Wikimedia Commons is used under a CC BY 3.0 (https://creativecommons.org/licenses/by/3.0) license.

Figure 14.3.5

CG_Heart Valve Animation by DrJanaOfficial on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license.

Figure 14.3.6

Heart_tee_four_chamber_view by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5 (https://creativecommons.org/licenses/by/2.5) license.

Figure 14.3.7

Circulation of blood through the heart by Christinelmiller on Wikimedia Commons is used under a CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) license. [Original image in the bottom right is by Wapcaplet / CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/)]

Figure 14.3.8

Human_healthy_pumping_heart_en.svg by Mariana Ruiz Villarreal [LadyofHats] on Wikimedia Common is released into the public domain (https://en.wikipedia.org/wiki/Public_domain).

Figure 14.3.9

Cardiac_Conduction_System by Cypressvine 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, June 19). Figure 19.12 Heart valves with the atria and major vessels removed [digital image].  In Anatomy and Physiology (Section 19.1). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/19-1-heart-anatomy#fig-ch20_01_04

Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436.

Heart and Stroke Foundation of Canada. (n.d.). https://www.heartandstroke.ca/

Sliwa, K., Zilla, P. (2017, December 7). 50th anniversary of the first human heart transplant—How is it seen today? European Heart Journal, 38(46):3402–3404. https://doi.org/10.1093/eurheartj/ehx695

Stanford Health Care. (2014, December 3). Total artificial heart option at Stanford (Includes surgical graphic footage). YouTube. https://www.youtube.com/watch?v=1PtxaxcPnGc&feature=youtu.be

TED. (2012, March 21). Noel Bairey Merz: The single biggest health threat women face. YouTube. https://www.youtube.com/watch?v=1bnzVjOJ6NM&feature=youtu.be

TEDx Talks. (2018, April 18). A change of heart: My transplant experience | Thomas Volk | TEDxUWLaCrosse. YouTube. https://www.youtube.com/watch?v=zU6mmix04PI&feature=youtu.be

UMagazine. (2015, Fall). The cutting edge: Patient first to bridge from experimental total artificial heart to transplant. UCLA Health. https://www.uclahealth.org/u-magazine/patient-first-to-bridge-from-experimental-total-artificial-heart-to-transplant

UnityPoint Health - Cedar Rapids. (2018, February 7). Watch a transcatheter aortic valve replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa. YouTube.  https://www.youtube.com/watch?v=jJm7zBcN6-M&feature=youtu.be

WMC Health. (2018, September 13). Heart transplant recipient meets donor family for the first time. YouTube. https://www.youtube.com/watch?v=biGuwQhuAsk&feature=youtu.be

 

 

 

A hollow, tube-like structure through which blood flows in the cardiovascular system; vein, artery, or capillary.

Image shows a photo of a young man.

Image shows a diagram of all the locations that chemical and mechanical digestion take place along the GI tract. In the mouth and pharynx, mechanical digestion includes chewing and swallowing and chemical digestion of carbohydrates and fats occurs. In the stomach, mechanical digestion includes peristaltic mixing and propulsion, and the chemical digestion of proteins and fats occurs. In the small intestine, mechanical digestion includes mixing and propulsion, and chemical digestion of carbohydrates, fats, polypeptides and nucleic acids takes place.

 

Twenty-six-year-old Hakeem wasn’t feeling well. He was more tired than usual, dragging through his workdays despite going to bed earlier, and napping on the weekends. He didn’t have much of an appetite, and had started losing weight. When he pressed on the side of his neck, like the doctor is doing in Figure 17.1.1, he noticed an unusual lump.

Hakeem went to his doctor, who performed a physical exam and determined that the lump was a swollen lymph node. Lymph nodes are part of the immune system, and they will often become enlarged when the body is fighting off an infection. Dr. Hayes thinks that the swollen lymph node and fatigue could be signs of a viral or bacterial infection, although he is concerned about Hakeem’s lack of appetite and weight loss. All of those symptoms combined can indicate a type of cancer called lymphoma. An infection, however, is a more likely cause, particularly in a young person like Hakeem. Dr. Hayes prescribes an antibiotic in case Hakeem has a bacterial infection, and advises him to return in a few weeks if his lymph node does not shrink, or if he is not feeling better.

Hakeem returns a few weeks later. He is not feeling better and his lymph node is still enlarged. Dr. Hayes is concerned, and orders a biopsy of the enlarged lymph node. A lymph node biopsy for suspected lymphoma often involves the surgical removal of all or part of a lymph node. This helps to determine whether the tissue contains cancerous cells.

The initial results of the biopsy indicate that Hakeem does have lymphoma. Although lymphoma is more common in older people, young adults and even children can get this disease. There are many types of lymphoma, with the two main types being Hodgkin's lymphoma and non-Hodgkin's lymphoma. Non-Hodgkin lymphoma (NHL), in turn, has many subtypes. The subtype depends on several factors, including which cell types are affected. Some subtypes of NHL, for example, affect immune system cells called B cells, while others affect different immune system cells called T cells.

Dr. Hayes explains to Hakeem that it is important to determine which type of lymphoma he has, in order to choose the best course of treatment. Hakeem’s biopsied tissue will be further examined and tested to see which cell types are affected, as well as which specific cell-surface proteins — called antigens — are present. This should help identify his specific type of lymphoma.

As you read this chapter, you will learn about the functions of the immune system, and the specific roles that its cells and organs — such as B and T cells and lymph nodes — play in defending the body. At the end of this chapter, you will learn what type of lymphoma Hakeem has and what some of his treatment options are, including treatments that make use of the biochemistry of the immune system to fight cancer with the immune system itself.

Attributions

Figure 17.1.1

Lymph nodes/Is it a Cold or the Flu  by Lee Health on Vimeo is used under Vimeo's Terms of Service (https://vimeo.com/terms#licenses).

Figure 17.1.2

mitchell-luo-ymo_yC_N_2o-unsplash [photo] by Mitchell Luo on Unsplash is used under the Unsplash License (https://unsplash.com/license).

Figure 17.1.3

Lymph node biopsy by US Army Africa on Flickr is used under a  CC BY 2.0 (https://creativecommons.org/licenses/by/2.0/) license.

References

Mayo Clinic Staff. (n.d.). Hodgkin's lymphoma [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/hodgkins-lymphoma/symptoms-causes/syc-20352646

Mayo Clinic Staff. (n.d.). Non-Hodgkin's lymphoma [online article]. MayoClinic.org. https://www.mayoclinic.org/diseases-conditions/non-hodgkins-lymphoma/symptoms-causes/syc-20375680

 

 

As described in the caption.

Genes causing a trait or disorder which are present on the X sex determining chromosome.

Created by CK-12 Foundation/Adapted by Christine Miller

This adorable nursing infant (Figure 9.4.1) is part of a positive feedback loop. When he suckles on the nipple, it sends nerve impulses to his mother’s hypothalamus. Those nerve impulses “tell” her pituitary gland to release the hormone prolactin into her bloodstream. Prolactin travels to the mammary glands in the breasts and stimulates milk production, which motivates the infant to keep suckling.

The pituitary gland is the master gland of the endocrine system, which is the system of glands that secrete hormones into the bloodstream. Endocrine hormones control virtually all physiological processes. They control growth, sexual maturation, reproduction, body temperature, blood pressure, and metabolism. The pituitary gland is considered the master gland of the endocrine system, because it controls the rest of the endocrine system. Many pituitary hormones either promote or inhibit hormone secretion by other endocrine glands.

The pituitary gland is about the size of a pea. It protrudes from the bottom of the hypothalamus at the base of the inner brain (see Figure 9.4.2). The pituitary is connected to the hypothalamus by a thin stalk (called the infundibulum). Blood vessels and nerves in the stalk allow direct connections between the hypothalamus and pituitary gland.

Anterior Lobe

The anterior pituitary is the lobe is at the front of the pituitary gland. It synthesizes and releases hormones into the blood. Table 9.4.1 shows some of the endocrine hormones released by the anterior pituitary, including their targets and effects.

Table 9.4.1

Endocrine Hormones Released by the Anterior Pituitary, and Their Targets and Effects.

Anterior Pituitary Hormone	Target	Effect
Adrenocorticotropic hormone (ACTH)	Adrenal glands	Stimulates the cortex of each adrenal gland to secrete its hormones.
Thyroid-stimulating hormone (TSH)	Thyroid gland	Stimulates the thyroid gland to secrete thyroid hormone.
Growth hormone (GH)	Body cells	Stimulates body cells to synthesize proteins and grow.
Follicle-stimulating hormone (FSH)	Ovaries, testes	Stimulates the ovaries to develop mature eggs.  stimulates the testes to produce sperm.
Luteinizing hormone (LH)	Ovaries, testes	Stimulates the ovaries and testes to secrete sex hormones; stimulates the ovaries to release eggs.
Prolactin (PRL)	Mammary glands	Stimulates the mammary glands to produce milk.

The anterior pituitary gland is regulated mainly by hormones from the hypothalamus. The hypothalamus secretes hormones (called releasing hormones and inhibiting hormones) that travel through capillaries directly to the anterior lobe of the pituitary gland. The hormones stimulate the anterior pituitary to either release or stop releasing particular pituitary hormones. Several of these hypothalamic hormones and their effects on the anterior pituitary are shown in the table below.

Table 9.4.2

Hypothalamic Hormones and Their Effects on the Anterior Pituitary

Hypothalamic Hormone	Effect on Anterior Pituitary
Thyrotropin releasing hormone (TRH)	Release of thyroid stimulating hormone (TSH)
Corticotropin releasing hormone (CRH)	Release of adrenocorticotropic hormone (ACTH)
Gonadotropin releasing hormone (GnRH)	Release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Growth hormone releasing hormone (GHRH)	Release of growth hormone (GH)
Growth hormone inhibiting hormone (GHIH) (Somatostatin)	Stopping of growth hormone release
Prolactin releasing hormone (PRH)	Release of prolactin
Prolactin inhibiting hormone (PIH) (Dopamine)	Stopping of prolactin release

Posterior Lobe

The posterior pituitary is the lobe is at the back of the pituitary gland. This lobe does not synthesize any hormones. Instead, the posterior lobe stores hormones that come from the hypothalamus along the axons of nerves connecting the two structures (also shown in Figure 9.4.2). The posterior pituitary then secretes the hormones into the bloodstream as needed. Hypothalamic hormones secreted by the posterior pituitary include vasopressin and oxytocin.

• Vasopressin (also called antidiuretic hormone, or ADH) helps maintain homeostasis in body water. It stimulates the kidneys to conserve water by producing more concentrated urine. Specifically, vasopressin targets ducts in the kidneys and makes them more permeable to water. This allows more water to be resorbed by the body, rather than excreted in urine.
• Oxytocin (OXY) targets cells in the uterus to stimulate uterine contractions, as in childbirth. It also targets cells in the breasts of a nursing mother to stimulate the letdown of milk.

Attributions

Figure 9.4.1

Breastfeeding by Petr Kratochvil  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 9.4.2

The_Hypothalamus-Pituitary_Complex 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 17.7 Hypothalamus–pituitary complex [digital image]. In Anatomy and Physiology (Section 17.3). OpenStax. https://openstax.org/books/anatomy-and-physiology/pages/17-3-the-pituitary-gland-and-hypothalamus

Swedish. (2012, April 19). Common pituitary diseases. YouTube. https://www.youtube.com/watch?v=jUKQFkmBuww&feature=youtu.be

UCSF Neurosurgery. (2015, May 13). Diagnosing and treating pituitary tumors - California Center for Pituitary Disorders at UCSF. YouTube. https://www.youtube.com/watch?v=v41AJGP-XmI&feature=youtu.be

Image shows a man at an oxygen bar. There are several erlenmeyer flasks of differently scented oxygen with tubes coming out of the top of each. The man is wearing a nasal cannula (tube that blows air into your nostrils).

Image shows a diagram of the heart with all chambers and major vessels labelled. Arrows indicate blood flow. Deoxygenated blood is brought the the right atrium by the superior and inferior vena cava. The right atrium moves blood into the right ventricle, which then sends blood to the lungs via the pulmonary arteries. Oxygenated blood returns to the heart from the lungs via the pulmonary veins and enters the left atrium. From there, blood is pumped into the left ventricle and then into the aorta for distribution to the body.

Image shows a diagram illustrating how peristalsis pushes food through the digestive tract by squeezing just behind the food, pushing it forward.

Having a higher proportion of hydronium ions than hydroxide ions; having the properties of an acid; having a pH below 7.

Image shows a diagram of the four steps of a white blood cell phagocytizing a bacterium. In the first stage, the white blood cell extends its plasma membrane to surround the bacteria and trap it inside a vesicle, very similar to endocytosis. In the next stage, a lysosome merges with the vesicle containing the bacterium; the digestive enzymes break down the bacterium, and the white blood cell absorbs the resulting nutrients.

The fusion of haploid gametes, egg and sperm, to form the diploid zygote.