case study #7 digestive system answers

23.1 Overview of the Digestive System

Learning objectives.

By the end of this section, you will be able to:

Identify the organs of the alimentary canal from proximal to distal, and briefly state their function
Identify the accessory digestive organs and briefly state their function
Describe the four fundamental tissue layers of the alimentary canal
Contrast the contributions of the enteric and autonomic nervous systems to digestive system functioning
Explain how the peritoneum anchors the digestive organs

The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body. Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process ( Figure 23.2 ).

As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body. Consider for example, the interrelationship between the digestive and cardiovascular systems. Arteries supply the digestive organs with oxygen and processed nutrients, and veins drain the digestive tract. These intestinal veins, constituting the hepatic portal system, are unique; they do not return blood directly to the heart. Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its circuit back to the heart. At the same time, the digestive system provides nutrients to the heart muscle and vascular tissue to support their functioning. The interrelationship of the digestive and endocrine systems is also critical. Hormones secreted by several endocrine glands, as well as endocrine cells of the pancreas, the stomach, and the small intestine, contribute to the control of digestion and nutrient metabolism. In turn, the digestive system provides the nutrients to fuel endocrine function. Table 23.1 gives a quick glimpse at how these other systems contribute to the functioning of the digestive system.

Digestive System Organs

The easiest way to understand the digestive system is to divide its organs into two main categories. The first group is the organs that make up the alimentary canal. Accessory digestive organs comprise the second group and are critical for orchestrating the breakdown of food and the assimilation of its nutrients into the body. Accessory digestive organs, despite their name, are critical to the function of the digestive system.

Alimentary Canal Organs

Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = “to nourish”) is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost. The main function of the organs of the alimentary canal is to nourish the body. This tube begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body. Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space.”

Accessory Structures

Each accessory digestive organ aids in the breakdown of food ( Figure 23.3 ). Within the mouth, the teeth and tongue begin mechanical digestion, whereas the salivary glands begin chemical digestion. Once food products enter the small intestine, the gallbladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue. Together, these are called accessory organs because they sprout from the lining cells of the developing gut (mucosa) and augment its function; indeed, you could not live without their vital contributions, and many significant diseases result from their malfunction. Even after development is complete, they maintain a connection to the gut by way of ducts.

Histology of the Alimentary Canal

Throughout its length, the alimentary tract is composed of the same four tissue layers; the details of their structural arrangements vary to fit their specific functions. Starting from the lumen and moving outwards, these layers are the mucosa, submucosa, muscularis, and serosa, which is continuous with the mesentery (see Figure 23.3 ).

The mucosa is referred to as a mucous membrane, because mucus production is a characteristic feature of gut epithelium. The membrane consists of epithelium, which is in direct contact with ingested food, and the lamina propria, a layer of connective tissue analogous to the dermis. In addition, the mucosa has a thin, smooth muscle layer, called the muscularis mucosae (not to be confused with the muscularis layer, described below).

Epithelium —In the mouth, pharynx, esophagus, and anal canal, the epithelium is primarily a non-keratinized, stratified squamous epithelium. In the stomach and intestines, it is a simple columnar epithelium. Notice that the epithelium is in direct contact with the lumen, the space inside the alimentary canal. Interspersed among its epithelial cells are goblet cells, which secrete mucus and fluid into the lumen, and enteroendocrine cells, which secrete hormones into the interstitial spaces between cells. Epithelial cells have a very brief lifespan, averaging from only a couple of days (in the mouth) to about a week (in the gut). This process of rapid renewal helps preserve the health of the alimentary canal, despite the wear and tear resulting from continued contact with foodstuffs.

Lamina propria —In addition to loose connective tissue, the lamina propria contains numerous blood and lymphatic vessels that transport nutrients absorbed through the alimentary canal to other parts of the body. The lamina propria also serves an immune function by housing clusters of lymphocytes, making up the mucosa-associated lymphoid tissue (MALT). These lymphocyte clusters are particularly substantial in the distal ileum where they are known as Peyer’s patches. When you consider that the alimentary canal is exposed to foodborne bacteria and other foreign matter, it is not hard to appreciate why the immune system has evolved a means of defending against the pathogens encountered within it.

Muscularis mucosae —This thin layer of smooth muscle is in a constant state of tension, pulling the mucosa of the stomach and small intestine into undulating folds. These folds dramatically increase the surface area available for digestion and absorption.

As its name implies, the submucosa lies immediately beneath the mucosa. A broad layer of dense connective tissue, it connects the overlying mucosa to the underlying muscularis. It includes blood and lymphatic vessels (which transport absorbed nutrients), and a scattering of submucosal glands that release digestive secretions. Additionally, it serves as a conduit for a dense branching network of nerves, the submucosal plexus, which functions as described below.

The third layer of the alimentary canal is the muscularis (also called the muscularis externa). The muscularis in the small intestine is made up of a double layer of smooth muscle: an inner circular layer and an outer longitudinal layer. The contractions of these layers promote mechanical digestion, expose more of the food to digestive chemicals, and move the food along the canal. In the most proximal and distal regions of the alimentary canal, including the mouth, pharynx, anterior part of the esophagus, and external anal sphincter, the muscularis is made up of skeletal muscle, which gives you voluntary control over swallowing and defecation. The basic two-layer structure found in the small intestine is modified in the organs proximal and distal to it. The stomach is equipped for its churning function by the addition of a third layer, the oblique muscle. While the colon has two layers like the small intestine, its longitudinal layer is segregated into three narrow parallel bands, the tenia coli, which make it look like a series of pouches rather than a simple tube.

The serosa is the portion of the alimentary canal superficial to the muscularis. Present only in the region of the alimentary canal within the abdominal cavity, it consists of a layer of visceral peritoneum overlying a layer of loose connective tissue. Instead of serosa, the mouth, pharynx, and esophagus have a dense sheath of collagen fibers called the adventitia. These tissues serve to hold the alimentary canal in place near the ventral surface of the vertebral column.

Nerve Supply

As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves. Without these nerves, not only would your food be without taste, but you would also be unable to feel either the food or the structures of your mouth, and you would be unable to avoid biting yourself as you chew, an action enabled by the motor branches of cranial nerves.

Intrinsic innervation of much of the alimentary canal is provided by the enteric nervous system, which runs from the esophagus to the anus, and contains approximately 100 million motor, sensory, and interneurons (unique to this system compared to all other parts of the peripheral nervous system). These enteric neurons are grouped into two plexuses. The myenteric plexus (plexus of Auerbach) lies in the muscularis layer of the alimentary canal and is responsible for motility , especially the rhythm and force of the contractions of the muscularis. The submucosal plexus (plexus of Meissner) lies in the submucosal layer and is responsible for regulating digestive secretions and reacting to the presence of food (see Figure 23.3 ).

Extrinsic innervations of the alimentary canal are provided by the autonomic nervous system, which includes both sympathetic and parasympathetic nerves. In general, sympathetic activation (the fight-or-flight response) restricts the activity of enteric neurons, thereby decreasing GI secretion and motility. In contrast, parasympathetic activation (the rest-and-digest response) increases GI secretion and motility by stimulating neurons of the enteric nervous system.

Blood Supply

The blood vessels serving the digestive system have two functions. They transport the protein and carbohydrate nutrients absorbed by mucosal cells after food is digested in the lumen. Lipids are absorbed via lacteals, tiny structures of the lymphatic system. The blood vessels’ second function is to supply the organs of the alimentary canal with the nutrients and oxygen needed to drive their cellular processes.

Specifically, the more anterior parts of the alimentary canal are supplied with blood by arteries branching off the aortic arch and thoracic aorta. Below this point, the alimentary canal is supplied with blood by arteries branching from the abdominal aorta. The celiac trunk services the liver, stomach, and duodenum, whereas the superior and inferior mesenteric arteries supply blood to the remaining small and large intestines.

The veins that collect nutrient-rich blood from the small intestine (where most absorption occurs) empty into the hepatic portal system. This venous network takes the blood into the liver where the nutrients are either processed or stored for later use. Only then does the blood drained from the alimentary canal viscera circulate back to the heart. To appreciate just how demanding the digestive process is on the cardiovascular system, consider that while you are “resting and digesting,” about one-fourth of the blood pumped with each heartbeat enters arteries serving the intestines.

The Peritoneum

The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue. It is composed of two different regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs ( Figure 23.4 ). The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces. A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum.

Disorders of the...

Digestive system: peritonitis.

Inflammation of the peritoneum is called peritonitis. Chemical peritonitis can develop any time the wall of the alimentary canal is breached, allowing the contents of the lumen entry into the peritoneal cavity. For example, when an ulcer perforates the stomach wall, gastric juices spill into the peritoneal cavity. Hemorrhagic peritonitis occurs after a ruptured tubal pregnancy or traumatic injury to the liver or spleen fills the peritoneal cavity with blood. Even more severe peritonitis is associated with bacterial infections seen with appendicitis, colonic diverticulitis, and pelvic inflammatory disease (infection of uterine tubes, usually by sexually transmitted bacteria). Peritonitis is life threatening and often results in emergency surgery to correct the underlying problem and intensive antibiotic therapy. When your great grandparents and even your parents were young, the mortality from peritonitis was high. Aggressive surgery, improvements in anesthesia safety, the advance of critical care expertise, and antibiotics have greatly improved the mortality rate from this condition. Even so, the mortality rate still ranges from 30 to 40 percent.

Interactive Link

By clicking on this link you can watch a short video of what happens to the food you eat, as it passes from your mouth to your intestine. Along the way, note how the food changes consistency and form. How does this change in consistency facilitate your gaining nutrients from food?

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Access for free at https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction

Authors: J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix
Publisher/website: OpenStax
Book title: Anatomy and Physiology 2e
Publication date: Apr 20, 2022
Location: Houston, Texas
Book URL: https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction
Section URL: https://openstax.org/books/anatomy-and-physiology-2e/pages/23-1-overview-of-the-digestive-system

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18.1: Case Study: Food Processing

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Page ID 16830

Suzanne Wakim & Mandeep Grewal
Butte College

Case Study: Please Don’t Pass the Bread

Rania and Tui 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. Rania says there is a particular restaurant she would like to go to because they are able to accommodate her dietary restrictions. Tui agrees and they head to the restaurant.

At lunch, Tui asks Rania what is special about her diet. Rania tells her that she can’t eat gluten. Tui says, “Oh yeah, 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.” Rania tells Tui that avoiding gluten isn’t optional for her—she has celiac disease. Eating even very small amounts of gluten could damage her digestive system.

You have probably heard of gluten—but what is it and why is it harmful to people with celiac disease? Gluten is a protein found in wheat and some other grains such as barley, rye, and oats. Therefore, it is commonly found in foods such as bread, pasta, baked goods, and many packaged foods. In 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. 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.

How can 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.

Chapter Overview: Digestive System

In this chapter, you will learn about the digestive system, which processes food so that our bodies can obtain nutrients. Specifically, you will learn about:

The structures and organs of the gastrointestinal (GI) tract through which food directly passes. This includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.
The functions of the GI tract, including mechanical and chemical digestion, absorption of nutrients, and the elimination of solid waste.
The accessory organs of digestion—the liver, gallbladder, and pancreas—secrete substances needed for digestion into the GI tract, in addition to other important functions.
Specializations of the tissues of the digestive system that allow it to carry out its functions.
How different types of nutrients such as carbohydrates, proteins, and fats are digested and absorbed by the body.
Beneficial bacteria that live in the GI tract and help us digest food, produce vitamins, and protect us from harmful pathogens and toxic substances.
Disorders of the digestive system, including inflammatory bowel diseases, ulcers, diverticulitis, and gastroenteritis (commonly known as “stomach flu”).

As you read this chapter, think about the following questions related to celiac disease:

What are the general functions of the small intestine? What do the villi in the small intestine do?
Why do you think celiac disease causes so many different types of symptoms and potentially serious complications?
What are some other autoimmune diseases that involve the body attacking its own digestive system?

Attributions

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178 Chapter 15 Answers: Digestive System

15.2 introduction to the digestive system: review questions and answers.

What is the digestive system? The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining food waste.
What are the three main functions of the digestive system? Define each function. The three main functions of the digestive system are digestion, absorption, and elimination. Digestion is the process of breaking down food into components that the body can absorb. It includes mechanical digestion and chemical digestion. Absorption is the process of taking up nutrients from food by body fluids for circulation to the rest of the body. Elimination is the process of excreting any remaining food waste after digestion and absorption are finished.
Self-marking
Relate the tissues in the walls of GI tract organs to the functions the organs perform. Digestion and/or absorption take place in all the organs of the GI tract. Organs of the GI tract have walls that consist of several tissue layers that enable them to carry out these functions. For example, the inner mucosa has cells that secrete digestive enzymes and other digestive substances and also cells that absorb nutrients. The muscle layer of the organs enables them to contract and relax in waves of peristalsis to move food through the GI tract.

15.3 Digestion and Absorption: Review Questions and Answers

Define digestion. Where does it occur? Digestion is a form of catabolism, in which food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs in the organs of the digestive system that make up the gastrointestinal tract.
Identify two organ systems that control the process of digestion by the digestive system. The process of digestion by the digestive system is controlled by the endocrine system and the nervous system.
What is mechanical digestion? Where does it occur? Mechanical digestion is a physical process in which food is broken into smaller pieces without becoming chemically changed. It occurs mainly in the mouth and stomach.
Describe chemical digestion. Chemical digestion is a chemical process in which macromolecules in food are broken down into simple nutrient molecules that can be absorbed into body fluids. Carbohydrates are chemically digested to sugars, proteins to amino acids, lipids to fatty acids, and nucleic acids to individual nucleotides.
What is the role of enzymes in chemical digestion? Chemical digestion requires digestive enzymes to catalyze the chemical reactions involved in digesting food.
What is absorption? When does it occur? Absorption is the process in which simple nutrient molecules are absorbed into blood or lymph. It occurs after the process of digestion.
Where does most absorption occur in the digestive system? Why does most of the absorption occur in this organ, and not earlier in the GI tract? The small intestine. Answers may vary. Sample answer: Food needs to be broken down into small nutrient molecules to be absorbed by the body. Food is increasingly broken down into smaller units through the process of digestion as it travels from the mouth to the small intestine. Therefore, many of the molecules are not small enough to be absorbed prior to the small intestine. Also, the small intestine has structural features that allow for absorption including villi, microvilli, and close proximity between the thin epithelial tissue and capillaries and lacteals that absorb nutrients into the blood and lymph.

15.4 Upper Gastrointestinal Tract: Review Questions and Answers

Identify structures in the mouth that are specialized for digestion. Structures in the mouth that are specialized for digestion include salivary glands, tongue, and teeth.
Describe digestion in the mouth. Both mechanical digestion and chemical digestion of carbohydrates and fats begin in the mouth.
What general role do the pharynx and esophagus play in the digestion of food? The pharynx and esophagus play the general role of transport by moving food from the mouth to the stomach.
How does food travel through the esophagus? Food travels through the esophagus by peristalsis. A wave of muscular contractions pushes food through the esophagus from the pharynx to the stomach.
Describe digestion in the stomach. Both mechanical and chemical digestion occur in the stomach. The squeezing and churning of stomach muscles mix and break food into smaller pieces. Acid and digestive enzymes secreted by the stomach start the chemical digestion of proteins. The stomach turns masticated food into a semi-fluid mixture called chyme.
Describe the differences between how air and food normally move past the pharynx. Air travels through the pharynx and into the larynx. When swallowing food, the epiglottis over the larynx closes, so that food doesn’t enter the larynx. The food then enters the esophagus.
Name two structures in the mouth that contribute to mechanical digestion. Answers may vary. Sample answer: Teeth and the hard palate.
What structure normally keeps stomach contents from backing up into the esophagus? The lower esophageal sphincter (sometimes referred to as the cardiac sphincter).
Thirty minutes after you eat a meal, where is most of your food located? Explain your answer. Thirty minutes after a meal, most of the food is located in the stomach because it takes about an hour for the stomach to turn the food into chyme, which it then passes on to the small intestine.
What are two roles of mucus in the upper GI tract? Two roles of mucus in the upper GI tract are: to moisten, soften, and lubricate food in the mouth; and to protect the stomach from damage from gastric acid.

15.5 Lower Gastrointestinal Tract: Review Questions and Answers

How is the mucosa of the small intestine specialized for digestion and absorption? The mucosa of the small intestine is specialized for digestion and absorption by being very wrinkled and covered with villi and microvilli, giving the small intestine a huge surface area for these processes.
What digestive substances are secreted into the duodenum? What compounds in food do they help digest? The duodenum secretes digestive enzymes including sucrase and lactase to digest disaccharides, as well as bicarbonate that helps to neutralize the acidic chyme entering the duodenum from the stomach. The chyme must be neutralized for digestive enzymes in the duodenum to do their work. The duodenum also receives bile from the liver or gallbladder to help neutralize acidity, and it receives digestive enzymes and bicarbonate from the pancreas. The digestive enzymes from the pancreas include amylase, which digests starches; trypsin and chymotrypsin, which digest proteins; and lipase, which digests lipids with the help of liver bile that breaks lipids into much smaller particles called micelles.
What is the main function of the jejunum? The main function of the jejunum is absorbing nutrients, including the absorption of simple sugars, amino acids, fatty acids, and many vitamins.
What roles does the ileum play? The small intestine consists of three parts: the duodenum, jejunum, and ileum.
The roles played by the ileum include digesting and absorbing any remaining nutrients. However, the main role of the ileum is to absorb vitamin B12 and bile salts.
How do beneficial bacteria in the large intestine help the human organism? Beneficial bacteria in the large intestine help digest certain compounds, produce vitamins, stimulate the immune system, and break down toxins, among other important functions for the human organism.
When diarrhea occurs, feces leaves the body in a more liquid state than normal. What part of the digestive system do you think is involved in diarrhea? Explain your answer The large intestine is involved in diarrhea because it is normally removes excess water from feces.
What causes intestinal gas, or flatulence? The bacterial breakdown of undigested polysaccharides in the large intestine produces nitrogen, carbon dioxide, methane, and other gases that are responsible for intestinal gas, or flatulence.

15.6 Accessory Organs of Digestion: Review Questions and Answers

Name three accessory organs of digestion. How do these organs differ from digestive organs that are part of the GI tract? Three accessory organs of digestion are the liver, gallbladder, and pancreas. Unlike digestive organs that are part of the GI tract, accessory organs are not directly involved in digestion or absorption because food does not actually pass through them. Instead, the accessory organs release substances needed for the chemical digestion of food in the duodenum of the small intestine.
Describe the liver and its blood supply. The liver is large organ in the abdomen that is divided into lobules consisting of metabolic hepatic cells. The liver receives oxygen in blood from the aorta through the hepatic artery. Through the portal vein, it receives nutrients in blood from the GI tract and wastes in blood from the spleen.
Explain the main digestive function of the liver and describe the components of bile and it’s importance in the digestive process. The main digestive function of the liver is the production of the alkaline liquid called bile. Bile goes directly to the duodenum through the common bile duct or to the gallbladder for storage until it is needed for digestion. Bile neutralizes acidic chyme that enters the duodenum from the stomach, which is necessary for digestive enzymes in the duodenum to work. Bile also emulsifies fat globules into smaller particles called micelles that are dispersed throughout the watery chyme and easier to digest chemically by the enzyme lipase.
What type of secretions does the pancreas release as part of each body system? Both the endocrine system and the digestive system include the pancreas. As an endocrine gland, the pancreas secretes endocrine hormones, such as insulin and glucagon that regulate blood sugar. As a digestive organ, the pancreas secretes digestive enzymes that help carry out chemical digestion in the duodenum.
List pancreatic enzymes that work in the duodenum, along with the substances they help digest. Pancreatic enzymes that work in the duodenum include amylase (starches), trypsin and chymotrypsin (proteins); lipase (lipids); and (deoxy)ribonucleases (DNA, RNA).
What are two substances produced by accessory organs of digestion that help neutralize chyme in the small intestine? Where are they produced? Two substances produced by accessory organs of digestion that help neutralize chyme are bile, which is produced by the liver; and bicarbonate, which is produced by the pancreas.
People who have their gallbladder removed sometimes have digestive problems after eating high-fat meals. Why do you think this happens? Answers may vary. Sample answer: The gallbladder stores and releases bile from the liver, which aids in the digestion of fats. When a person has their gallbladder removed, they will not have this additional storage and release of bile, and may therefore have trouble digesting high-fat meals.
Which accessory organ of digestion synthesizes cholesterol? The liver

15.7 Disorders of the Gastrointestinal Tract: Review Questions and Answers

Compare and contrast Crohn’s disease and ulcerative colitis. Crohn’s disease and ulcerative colitis are the two principal inflammatory bowel diseases. They have similar causes, symptoms, and treatments. However, Crohn’s disease may affect any part of the GI tract from the mouth to the anus among other body tissues, whereas ulcerative colitis affects only the colon and/or rectum.
How are diverticulosis and diverticulitis related? Diverticulosis found in some people in which the lining of the large intestine develops little pouches called diverticula. People with diverticulosis may develop diverticulitis, in which one or more of the diverticula become infected and inflamed. Diverticulitis is generally treated with antibiotics and bowel rest; sometimes surgery is required.
Identify the cause of giardiasis. Why may it cause malabsorption? Giardiasis is a type of gastroenteritis caused by infection of the GI tract with the protozoa parasite Giardia lamblia . This infection may cause malabsorption because the parasites inhibit intestinal digestive enzyme production and cause detrimental changes to microvilli.
Name three disorders of the GI tract that can be caused by bacteria. Answers may vary. Sample answer: Gastroenteritis, diverticulitis, and peptic ulcers.
Name one disorder of the GI tract that can be helped by anti-inflammatory medications, and one that can be caused by chronic use of anti-inflammatory medications. Inflammatory bowel disease can be helped by anti-inflammatory medications and peptic ulcers can be caused by chronic use of non-steroidal anti-inflammatory medications.
Describe one reason why it can be dangerous to drink untreated water. Answers may vary. Sample answer: Giardiasis often occurs when people drink untreated water that contains G. lamblia .

15.8 Case Study Conclusion and Chapter Summary: Review Questions and Answers

Explain how the accessory organs of digestion interact with the GI tract. The accessory organs of digestion are all involved in secreting substances needed for chemical digestion into the duodenum of the small intestine, which is part of the GI tract.
If the pH in the duodenum was too low (acidic), what effect do you think this would have on the processes of the digestive system? Answers may vary. Sample answer: I think that if the pH in the duodenum were too acidic, digestion would be impaired because digestive enzymes in the duodenum require a more alkaline environment in which to work.
Discuss whether digestion occurs in the large intestine. Answers may vary. Sample answer: Although what we normally think of as digestion is completed before food reaches the large intestine, remaining food is further broken down in the large intestine by fermentation by bacteria. So in a sense, food is “digested” in the large intestine, but it is due to the activity of microorganisms living there and not the organ itself.
Lipids are digested at different points in the digestive system. Describe how lipids are digested at two of these points. Answers may vary. Sample answer: Lipids staring being chemically digested in the mouth by lipase from the salivary glands. Most lipid digestion occurs in the small intestine. Bile from the liver and gall bladder emulsifies lipids into smaller globules called micelles in the small intestine. Lipase from the pancreas then further digests the lipids in the small intestine into individual fatty acid molecules.
Describe two different functions of stomach acid. Answers may vary. Sample answer: Stomach acid lowers the pH to a level that is required for digestive enzymes in the stomach, such as pepsin, to work. Stomach acid also can kill pathogens that enter the digestive system.
Name and describe the location and function of three of the valves of the GI tract. Esophageal sphincter, pyloric sphincter, ileocecal sphincter.
What is the name of the rhythmic muscle contractions that move food through the GI tract? Peristalsis.
What are the major roles of the upper GI tract? Answers may vary. Sample answer: The major roles of the upper GI tract are to start the digestion process and to move food further down into the lower GI tract.
What is the physiological cause of heartburn? Heartburn is due to the contents of the stomach backing up into the esophagus, usually due to a failure of the lower esophageal sphincter to remain completely closed.
What are two ways in which the tongue participates in digestion? Answers will vary. Sample answer: The tongue helps move food so that it can be chewed and swallowed. It also contains taste receptors which, when activated, stimulate the secretion of saliva from the salivary glands which helps digest food by moistening it and chemically digesting it with enzymes.
Where is the epiglottis located? If the epiglottis were to not close properly, what might happen? The epiglottis is a flap of cartilage located at the opening of the larynx. If the epiglottis were to not close properly, food might enter the larynx where air normally travels.

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Chapter 7 Answers: Introduction to the Human Body

7.2 organization of the body.

How is the human body like a complex machine? Like a complex machine, the human body consists of multiple parts that work together to perform certain functions.
Describe the difference between human anatomy and human physiology. Human biology incorporates both human anatomy and human physiology. Human anatomy is the body’s structure, and human physiology is the body’s functioning.
Self-marking
Relate cell structure to cell function, and give examples of specific cell types in the human body. Besides maintaining basic life processes, most human cells carry out special functions, and their structures reflect their functions. Examples may vary. Sample answer: Examples of specific cell types in the human body include blood cells, bone cells, and neurons.
Define tissue, and identify the four types of tissues that make up the human body. A tissue is a group of connected cells that have a similar function. The four types of tissues that make up the human body include connective, epithelial, muscle, and nervous tissues.
What is an organ? Give three examples of organs in the human body. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples may vary. Sample answer: Three examples of organs in the human body are the heart, brain, and lungs.
Define organ systems. Name five examples in the human body. An organ system is a group of organs that work together to carry out a complex overall function, with each organ in the system doing part of the larger job. Examples may vary. Sample answer: Five organ systems in the human body are the skeletal, muscular, digestive, respiratory, and nervous systems.
How is the human body regulated so all of its organs and organ systems work together? The human body is regulated by the nervous and endocrine systems so all of its organs and organ systems work together. The nervous system controls virtually all body activities, and the endocrine system secretes hormones that help to regulate these activities.
Which organ system’s function is to provide structure to the body and protect internal organs? Skeletal system.
Give one example of how the respiratory and circulatory systems work together. Answers may vary. Sample answer: The respiratory system takes in oxygen and the circulatory system transports oxygen throughout the body.

7.3 Cells and Tissues: Review Questions and Answers

Give an example of cells that function individually and move freely. Additionally, give an example of cells that act together and are attached to other cells of the same type. Examples may vary. Sample answer: An example of cells that function individually and move freely is red blood cells. An example of cells that act together and are attached to other cells of the same type is epithelial cells.
What is an example of cells that can readily divide? What is an example of cells that can divide only under rare circumstances? Examples may vary. Sample answer: An example of cells that can readily divide are skin cells. An example of cells that can divide only under rare circumstances are certain nerve cells.
Identify a type of cell that secretes an important substance. Name the substance it secretes. Answers may vary. Sample answer: A type of cell that secretes an important substance is the type of pancreatic cell that secretes insulin, the hormone that regulates the level of glucose in the blood.
Explain how different cell types come about when all the cells in an individual human being are genetically identical. The differential regulation of genes explains how different cell types come about when all the cells in an individual human being are genetically identical. Cells with the same genes can be very different because different genes are expressed depending on the cell type.
Compare and contrast four sub-types of human bone cells. Four sub-types of human bone cells are osteocytes, osteoblasts, osteogenic cells, and osteoclasts. All four are located in human bones, but each has a different form and function. Osteocytes are star-shaped bone cells that make up most of mature bone. Osteoblasts are immature bone cells that synthesize new bone. Osteogenic cells are undifferentiated stem cells that differentiate to form osteoblasts. Osteoclasts are very large, multinucleated cells that are responsible for the breakdown of bones through resorption.
Identify three types of human white blood cells. State their functions. Answers may vary. Sample answer: Three types of human white blood cells are monocytes, which phagocytize pathogens in tissues; eosinophils, which attack larger parasites and set off allergic responses; and neutrophils, which phagocytize single-celled bacteria and fungi in the blood.
Why are bone and blood both classified as connective tissues? Connective tissues are made up of living cells that are separated by non-living material, called extracellular matrix, which can be solid or liquid. Bone and blood both have extracellular matrix. In bone, this matrix consists of a rigid mineral framework. In blood, this matrix consists of liquid plasma.
Name another type of connective tissue. Describe its role in the human body. Answers may vary. Sample answer: Another type of connective tissues is areolar tissue. It is found in the skin and mucous membranes, where it binds the skin or membrane to underlying tissues such as muscles.
Based on the information above about types of epithelial tissues, list four general ways this type of tissue functions in the human body. Answers may vary. Sample answer: Four general functions of epithelial tissues are secreting substances, absorbing substances, protecting other tissues, and allowing organs to expand and stretch.
Compare and contrast the three types of muscle tissues. The three types of muscle tissues are skeletal, smooth, and cardiac muscle tissues. Skeletal muscles are striated, attached to bones, and under voluntary control. Smooth muscles are nonstriated, found in the walls of blood vessels and internal organs, and not under voluntary control. Cardiac muscles are striated, found only in the heart, and not under voluntary control.
Identify the two main types of cells that make up nervous tissue. Compare their general functions. The two main types of cells that make up nervous tissue are neurons and glial cells. Neurons directly transmit messages, usually through an electrochemical process, while glial cells play more of a supporting role.
Of the main types of human tissue, name two that can secrete hormones. Answers may vary. Sample answer: epithelial endocrine glandular tissue, as found in the pancreas, and nervous tissues, which can send out neurotransmitters.
Cells in a particular tissue… (C) Work together to carry out a function.
Why are mucus membranes often located in regions that interface between the body and the outside world? Answers may vary. Sample answer: Mucus is a slimy substance that traps pathogens, particles, and debris from the outside world to protect the body. Therefore, the mucus membranes that produce it are often located in regions of the body that interface with the outside world.
Skin is a type of epithelial tissue .
Body fat is a type of connective tissue.

7.4 Tissues: Review Questions and Answers

Define the term tissue. A cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
If a part of the body needed a lining that was both protective, but still able to absorb nutrients, what would be the best type of epithelial tissue to use? Simple cuboidal or simple columnar epithelial tissue.
Where do you find skeletal muscle? Smooth muscle? Cardiac muscle? Skeletal muscle is found attached to bones. Smooth muscle is found in walls of tubes in the body. Cardiac muscle is found in the heart.
What are some of the functions of neuroglia? To provide nutrients to neurons, to create the myelin sheath for neural axons, and to remove debris and cellular waste from neurons.

7.5 Human Organs and Organ Systems: Review Questions and Answers

What is the primary tissue in the heart, and what is its role? The main tissue in the heart is cardiac muscle. Its role is to pump blood by making the heart beat.
What non-muscle tissues are found in the heart? What are their functions? Non-muscle tissues in the heart include nervous tissues, which control the beating of the heart; and connective tissues, which make up heart valves that keep blood flowing in just one direction through the heart.
Identify two vital organs in the human body. Identify their locations and functions. Answers may vary. Sample answer: Two vital organs in the human body are the heart and brain. The heart is located in the centre of the chest, and its function is to keep blood flowing through the body. The brain is located in the head, and it function is to act as the body’s control centre.
List three human organ systems. For each organ system, identify some of its organs and functions. Answers may vary. Sample answer: Three human organ systems are the integumentary, skeletal, and muscular systems. Organs of the integumentary system include skin, hair, and nails. Functions of the integumentary system include enclosing internal body structures and providing a site for sensory receptors. Organs of the skeletal system include bones and joints. Functions of the skeletal system include supporting the body and enabling movement. Organs of the muscular system include skeletal muscles and tendons. Functions of the muscular system include enabling movement and helping to regulate body temperature.
Compare and contrast the male and female reproductive systems. Both male and female reproductive systems produce sex-specific sex hormones and gametes, but the organs involved in these processes are different. The male reproductive system includes the epididymis, testes, and penis. The female reproductive system includes the uterus, ovaries, and mammary glands. The male and female systems also have different additional roles. For example, the male system delivers gametes to the female reproductive tract, whereas the female system supports an embryo and fetus until birth and also produces milk for the infant after birth.
skeletal system and muscular system The skeletal system and muscular system work together to enable movement of the body.
muscular system and digestive system Smooth muscle tissue in the digestive system allows food to move through it.
endocrine system and reproductive system Some organs in the reproductive system, such as the ovaries and testes, are also in the endocrine system because they produce hormones.
cardiovascular system and urinary system Blood in the cardiovascular system is filtered by the urinary system to remove excess water and the waste product urea.
What is the largest organ of the human body? The skin.
What are three organ systems involved in regulating human body temperature? The cardiovascular system, the integumentary system, and the muscular system.

7.6 Human Body Cavities: Review Questions and Answers

What is a body cavity? A body cavity is a fluid-filled space inside the body that holds and protects internal organs.
Compare and contrast the ventral and dorsal body cavities. The ventral and dorsal body cavities are the two major human body cavities. Each is subdivided into smaller body cavities. The ventral cavity is at the front of the body, whereas the dorsal cavity is at the back of the body. The ventral cavity includes just the trunk; the dorsal cavity includes the head as well as the trunk.
Identify the subdivisions of the ventral cavity, and the organs each contains. The ventral cavity is subdivided into the thoracic cavity, which contains the lungs and heart, and the abdominopelvic cavity, which contains the kidneys digestive and reproductive organs.
Describe the subdivisions of the dorsal cavity and their contents. The dorsal cavity is subdivided into the cranial cavity and the spinal cavity. The cranial cavity fills most of the upper part of the skull and contains the brain. The spinal cavity is long and narrow and runs throughout the vertebral column. It contains the spinal cord.
Identify and describe all the tissues that protect the brain and spinal cord. The brain and spinal cord are protected by the bones of the skull and the vertebrae of the vertebral column. Within the bones, the brain and spinal cord are protected by the meninges, which is a three-layer membrane that encloses the brain and spinal cord. In addition, between two of the layers of the meninges, the brain and spinal cord are protected and cushioned by a thin layer of cerebrospinal fluid.
What do you think might happen if fluid were to build up excessively in one of the body cavities? Answers may vary. Sample answer: I think that if fluid were to build up excessively in one of the body cavities, it could put pressure on the organs inside of it, which might cause problems with their functioning.
Explain why a woman’s body can accommodate a full-term fetus during pregnancy without damaging her internal organs. Answers may vary. Sample answer: There is room within the ventral body cavity for organs to expand — such as the uterus that holds the fetus — without interfering with other internal organs.
Which body cavity does the needle enter in a lumbar puncture? The spinal cavity
What are the names given to the three body cavity divisions where the heart is located?What are the names given to the three body cavity divisions where the kidneys are located? Ventral, thoracic, and pericardial. Ventral, abdominopelvic, and abdominal.

7.7 Interactions of Organ Systems: Review Questions and Answers

What is the autonomic nervous system? The autonomic nervous system is the part of the nervous system that controls involuntary functions, such as heart rate, blood flow, and digestion.
How do the autonomic nervous system and endocrine system communicate with other organ systems so the systems can interact? The autonomic nervous system sends out messages via chemical messengers called neurotransmitters that communicate with other parts of the nervous system or with other organ systems. The endocrine system consists of glands that secrete hormones directly into the bloodstream. These hormones can affect cells anywhere in the body.
Explain how the brain communicates with the endocrine system. The brain communicates with the endocrine system via a part of the brain called the hypothalamus. The hypothalamus secretes hormones that travel directly to cells of an endocrine gland called the pituitary, which is located beneath the hypothalamus. The pituitary gland controls the rest of the endocrine system.
What is the role of the pituitary gland in the endocrine system? The pituitary gland is the master gland of the pituitary system. Most of its hormones either turn on or turn off other endocrine glands.
Identify the organ systems that play a role in cellular respiration. Organ systems that play a role in cellular respiration include the digestive, cardiovascular, and respiratory systems.
How does the hormone adrenaline prepare the body to fight or flee? What specific physiological changes does it bring about? Adrenaline floods the circulation and affects other organ systems throughout the body, including the cardiovascular, respiratory, and digestive systems. Specific responses include increased heart rate, more rapid breathing, and a shunting of blood away from the digestive system and toward the muscles, brain, and other vital organs needed for fight or flight.
Explain the role of the muscular system in digesting food. Food passes through the organs of the digestive tract by rhythmic contractions of muscles in the walls of the organs.
Describe how three different organ systems are involved when a player makes a particular play in hockey, such as catching a fly ball. Answers may vary. Sample answer: Three organ systems that are involved when a player catches a fly ball include the nervous system, muscular system, and skeletal system. The player sees the ball and decides to go for it (nervous system). The player runs toward the ball and reaches out to catch it (muscular and skeletal systems).
What are two types of molecules that the body uses to communicate between organ systems? Neurotransmitters and hormones.
Explain why hormones can have such a wide variety of effects on the body. Answers may vary. Sample answer: Hormones can have a wide variety of effects on the body because they travel throughout the body via the bloodstream, so they can affect many different organ systems.

7.8 Homeostasis and Feedback: Review Questions and Answers

Compare and contrast negative and positive feedback loops. Both negative and positive feedback loops are cycles that control a variable by feeding back to change its value. In a negative feedback loop, feedback serves to reduce an excessive response and keep a variable within the normal range. In a positive feedback loop, feedback serves to intensity a response until an end point is reached.
Explain how negative feedback controls body temperature. The human body’s temperature regulatory centre is the hypothalamus in the brain. When the hypothalamus receives data from sensors in the skin and brain that body temperature is higher or lower than the set point, it sets into motion responses that bring the temperature back to the set point. For example, if body temperature is higher than the set point, the hypothalamus sets into motion the following responses: blood vessels in the skin dilate to allow more heat to come to the body surface where it can be radiated into the environment; sweat glands in the skin are activated to increase their output of sweat so there can be more evaporative cooling; and breathing becomes deeper to increase heat loss from the lungs.
Give two examples of physiological processes controlled by positive feedback loops. Two examples of physiological processes that are controlled by positive feedback loops are blood clotting and childbirth.
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? Answers may vary. Sample answer: Having a positive feedback loop for milk production helps the mother’s body produce enough milk for the baby, but not too much, because the amount of milk is matched to the amount that the baby nurses. That way the baby can be sufficiently fed without the mother’s body dedicating extra energy to making more milk than is needed. I think this would be beneficial evolutionarily by increasing the chance of survival for both the mother and the baby.
Explain why homeostasis is regulated by negative feedback loops, rather than positive feedback loops. Answers may vary. Sample answer: Homeostasis is regulated by negative feedback loops, rather than positive feedback loops, because negative feedback loops serve to keep a variable within a normal range by preventing an excessive response. Homeostasis is a steady state where the body functions optimally, or at least normally. In positive feedback loops, a response is intensified instead of remaining steady.
What is the stimulus in this system? Explain your answer. Testosterone (T) is the stimulus, because it is the variable being regulated.
What is the control centre in this system? Explain your answer. The cells in the hypothalamus that produce GnRH are the control centre, because this is the region that matches T levels with normal levels and then adjusts output of GnRH accordingly.
In this system, is the pituitary considered the stimulus, sensor, control centre, or effector? Explain your answer. The pituitary is an effector in this system because it acts on a signal from the control centre (the hypothalamus) to move the variable (T) back to its set point by releasing more or less LH.

7.9 Case Study Conclusion: Review Questions and Answers

Compare and contrast tissues and organs. Answers may vary. Sample answer: Tissues and organs are both units within the body that carry out a particular function, and are composed of cells. Tissues, however, consist of cells that have similar properties, while organs are made up of two or more types of tissue. Organs are generally more structurally complex than tissues.
Which type of tissue lines the inner and outer surfaces of the body? Epithelial.
What is a vital organ? What happens if a vital organ stops working? A vital organ is an organ that is necessary for survival. If a vital organ stops working, death will occur unless there is medical intervention to keep the person alive.
Name three organ systems that transport or remove wastes from the body. Answers will vary but may include: the digestive system, integumentary system, cardiovascular system, urinary system, and respiratory system.
Name two types of tissue in the digestive system. Answers may vary. Sample answer: Epithelial tissue (such as mucous membranes) and muscle tissue.
Describe one way in which the integumentary and cardiovascular systems work together to regulate homeostasis in the human body. Answers may vary. Sample answer: The skin in the integumentary system and blood and blood vessels are in the cardiovascular system. One way in which the body regulates body temperature is to dilate or constrict the blood vessels at the skin’s surface to either dissipate or conserve heat at the skin. In this way, the integumentary and cardiovascular systems work together to regulate homeostasis of body temperature.
True or False: Body cavities are filled with air. False.
In which organ system is the pituitary gland? Describe how the pituitary gland increases metabolism. The pituitary gland secretes thyroid stimulating hormone, which travels through the circulation to the thyroid gland, which is then stimulated to secrete thyroid hormone. Thyroid hormone then travels to cells throughout the body, where it increases their 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? Positive feedback.
What is the stimulus in this feedback loop? The level of molecule B1.
If the level of B1 falls significantly below the set point, what do you think happens to the production of A1? Why? Answers may vary. Sample answer: A1 will likely increase because the level of B1 has dropped below the normal range and the system is trying to maintain homeostasis. A1 increases in order to increase the level of B1.
What is the effector in this feedback loop? Organ B.
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? Answers may vary. Sample answer: I think A1 and B1 are most likely hormones because the endocrine system secretes hormones. Also, hormones are messenger molecules that are often involved in regulation of homeostasis.
What are the two main systems that allow various organ systems to communicate with each other? The autonomic nervous system and endocrine system.
What are two functions of the hypothalamus? Answers will vary but may include: controlling the endocrine system, regulating body temperature, and controlling the process of childbirth.

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23.1 Overview of the Digestive System

Learning objectives.

By the end of this section, you will be able to:

Describe the organs of the alimentary canal from proximal to distal, and briefly state their function
Identify the accessory digestive organs and briefly state their function
Describe the four fundamental tissue layers of the alimentary canal and the function of each layer
Contrast the contributions of the enteric and autonomic nervous systems to digestive system functioning
Explain how the peritoneum anchors the digestive organs

This diagram shows the digestive system of a human being, with the major organs labeled.

As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body. Consider for example, the interrelationship between the digestive and cardiovascular systems. Arteries supply the digestive organs with oxygen and processed nutrients, and veins drain the digestive tract. These intestinal veins, constituting the hepatic portal system, are unique in that they do not return blood directly to the heart. Rather, this blood is diverted to the liver where its nutrients are off-loaded for processing before blood completes its circuit back to the heart. At the same time, the digestive system provides nutrients to the heart muscle and vascular tissue to support their functioning. The interrelationship of the digestive and endocrine systems is also critical. Hormones secreted by several endocrine glands, as well as endocrine cells of the pancreas, the stomach, and the small intestine, contribute to the control of digestion and nutrient metabolism. In turn, the digestive system provides the nutrients to fuel endocrine function. Table 23.1 gives a quick glimpse at how these other systems contribute to the functioning of the digestive system.

Digestive System Organs

Alimentary Canal Organs

Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = “to nourish”) is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length when measured after death, once smooth muscle tone is lost. The main function of the organs of the alimentary canal is to nourish the body by digesting food and absorbing released nutrients. This tube begins at the mouth and terminates at the anus. Between those two points, the canal is modified as the pharynx, esophagus, stomach, and small and large intestines to fit the functional needs of the body. Both the mouth and anus are open to the external environment; thus, food and wastes within the alimentary canal are technically considered to be outside the body. Only through the process of absorption do the nutrients in food enter into and nourish the body’s “inner space.”

Accessory Structures

Each accessory digestive organ aids in the breakdown of food ( Figure 23.1.2 ). Within the mouth, the teeth and tongue begin mechanical digestion, whereas the salivary glands begin chemical digestion. Once food products enter the small intestine, the gallbladder, liver, and pancreas release secretions—such as bile and enzymes—essential for digestion to continue. Together, these are called accessory organs because they sprout from the lining cells of the developing gut (mucosa) and augment its function; indeed, you could not live without their vital contributions, and many significant diseases result from their malfunction. Even after development is complete, they maintain a connection to the gut by way of ducts.

Histology of the Alimentary Canal

This image shows the cross section of the alimentary canal. The different layers of the alimentary canal are shown as concentric cylinders with major muscles and veins labeled.

The mucosa is referred to as a mucous membrane, because mucus production is a characteristic feature of gut epithelium. The membrane consists of epithelium, which is in direct contact with ingested food, and the lamina propria, a layer of connective tissue analogous to the dermis. In addition, the mucosa has a thin, smooth muscle layer, called the muscularis mucosa (not to be confused with the muscularis layer, described below).

Muscularis mucosa —This thin layer of smooth muscle is in a constant state of tension, pulling the mucosa of the stomach and small intestine into undulating folds. These folds dramatically increase the surface area available for digestion and absorption.

The third layer of the alimentary canal is the muscalaris (also called the muscularis externa). The muscularis in the small intestine is made up of a double layer of smooth muscle: an inner circular layer and an outer longitudinal layer. The contractions of these layers promote mechanical digestion, expose more of the food to digestive chemicals, and move the food along the canal. In the most proximal and distal regions of the alimentary canal, including the mouth, pharynx, anterior part of the esophagus, and external anal sphincter, the muscularis is made up of skeletal muscle, which gives you voluntary control over swallowing and defecation. The basic two-layer structure found in the small intestine is modified in the organs proximal and distal to it. The stomach is equipped for its churning function by the addition of a third layer, the oblique muscle. While the colon has two layers like the small intestine, its longitudinal layer is segregated into three narrow parallel bands, the tenia coli, which make it look like a series of pouches rather than a simple tube.

Nerve Supply

Blood Supply

The Peritoneum

The digestive organs within the abdominal cavity are held in place by the peritoneum, a broad serous membranous sac made up of squamous epithelial tissue surrounded by connective tissue. It is composed of two different regions: the parietal peritoneum, which lines the abdominal wall, and the visceral peritoneum, which envelopes the abdominal organs ( Figure 23.1.3 ). The peritoneal cavity is the space bounded by the visceral and parietal peritoneal surfaces. A few milliliters of watery fluid act as a lubricant to minimize friction between the serosal surfaces of the peritoneum.

The visceral peritoneum includes multiple large folds that envelope various abdominal organs, holding them to the dorsal surface of the body wall. Within these folds are blood vessels, lymphatic vessels, and nerves that innervate the organs with which they are in contact, supplying their adjacent organs. The five major peritoneal folds are described in Table 23.2 . An important one of these folds is the mesentery which attaches the small intestine to the body wall allowing for blood vessels, nerves, and lymphatic vessels to have a secure structure to travel through on their way to and from the small intestine. The mesocolon is the portion of the mesentery serving the colon and is considered part of the larger mesentery organ. Note that during fetal development, certain digestive structures, including the first portion of the small intestine (called the duodenum), the pancreas, and portions of the large intestine (the ascending and descending colon, and the rectum) remain completely or partially posterior to the peritoneum. Thus, the location of these organs is described as retroperitoneal .

External Website

Chapter Review

The digestive system includes the organs of the alimentary canal and accessory structures. The alimentary canal forms a continuous tube that is open to the outside environment at both ends. The organs of the alimentary canal are the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The accessory digestive structures include the teeth, tongue, salivary glands, liver, pancreas, and gallbladder. The wall of the alimentary canal is composed of four basic tissue layers: mucosa, submucosa, muscularis, and serosa. The enteric nervous system provides intrinsic innervation, and the autonomic nervous system provides extrinsic innervation.

Interactive Link Questions

By clicking on this link , you can watch a short video of what happens to the food you eat as it passes from your mouth to your intestine. Along the way, note how the food changes consistency and form. How does this change in consistency facilitate your gaining nutrients from food?

Answers may vary.

Review Questions

Critical thinking questions.

1. Explain how the enteric nervous system supports the digestive system. What might occur that could result in the autonomic nervous system having a negative impact on digestion?

2. What layer of the alimentary canal tissue is capable of helping to protect the body against disease, and through what mechanism?

Answers for Critical Thinking Questions

The enteric nervous system helps regulate alimentary canal motility and the secretion of digestive juices, thus facilitating digestion. If a person becomes overly anxious, sympathetic innervation of the alimentary canal is stimulated, which can result in a slowing of digestive activity.
The lamina propria of the mucosa contains lymphoid tissue that makes up the MALT and responds to pathogens encountered in the alimentary canal.

This work, Anatomy & Physiology, is adapted from Anatomy & Physiology by OpenStax , licensed under CC BY . This edition, with revised content and artwork, is licensed under CC BY-SA except where otherwise noted.

Images, from Anatomy & Physiology by OpenStax , are licensed under CC BY except where otherwise noted.

Access the original for free at https://openstax.org/books/anatomy-and-physiology/pages/1-introduction .

Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License , except where otherwise noted.

Biology Article

Human Digestive System

Digestive system of humans.

The digestive tract of humans starts with the mouth and ends with the anus. It includes different structures such as the mouth, oesophagus, pancreas, stomach, small intestine, large intestine, liver, gall bladder, and anus.

Introduction Structure Parts

Small Intestine

Large Intestine

Accessory organs, digestion process.

Mixing and Movement

Disorders Functions Notes

The Human Digestive System

The digestive system of the human body comprises a group of organs working together to convert food into energy for the body. Anatomically, the digestive system is made up of the gastrointestinal tract, along with accessory organs such as the liver, pancreas and gallbladder. The hollow organs that make up the gastrointestinal tract (GI tract) include the mouth, stomach, oesophagus, small intestine and large intestine that contains the rectum and anus.

Human Digestive System and Nutrition involve the intake of food by an organism and its utilization for energy. This is a vital process which helps living beings to obtain their energy from various sources. The food which we eat undergoes much processing before the nutrients present in them are utilized to generate energy. This processing is known as digestion. Humans and other animals have specialized organs and systems for this process.

The digestion process involves the alimentary canal along with various accessory organs and organ systems. In humans, the process is quite simple due to our monogastric nature. This means that we have a one-chambered stomach, unlike other animals such as cows, which have four chambers.

Some parts of nervous and circulatory systems also play a significant role in the digestion process. A combination of nerves, bacteria, hormones, blood and other organs of the digestive system completes the task of digestion.

Let us have a detailed look at the human digestive system, its parts and functions. Also provided at the end of the chapter are digestive system notes.

Diagram Of The Human Digestive System

The diagram given below represents different parts of the human digestive system that convert food into essential nutrients absorbed by the body.

Parts of the Human Digestive System

The digestive system of the human body comprises a group of organs that work together in converting food into energy and other basic nutrients to power the body. The food we take in is digested and utilized by our body, and the unused parts of the food are defecated.

The digestive system of the human body is the sum of the gastrointestinal tract (GIT; also called alimentary canal) and accessory organs (tongue, liver, pancreas, etc.). These two parts together help in the digestion process.

The alimentary canal is the long tube through which the food that we eat is passed. It begins at the mouth (buccal or oral cavity), passes through the pharynx, oesophagus or food pipe, stomach, small intestines, large intestines, rectum and finally ends at the anus. The food particles gradually get digested as they travel through various compartments of the alimentary canal.

Accessory organs are organs which participate in the digestion process but are not actually a part of GIT. They stimulate the digestion by releasing certain enzymes that help in breaking down the food.

Let us have a detailed look at the digestive system of the human body, along with its parts and functions:

Food starts its journey from the mouth or the oral cavity. There are many other organs that contribute to the digestion process, including teeth, salivary glands, and tongue. Teeth are designed for grinding food particles into small pieces and are moistened with saliva before the tongue pushes the food into the pharynx.

A fibromuscular y-shaped tube attached to the terminal end of the mouth. It is mainly involved in the passage of chewed/crushed food from the mouth through the oesophagus. It also has a major part in the respiratory system, as air travels through the pharynx from the nasal cavity on its way to the lungs.

This is a muscular tube that connects the pharynx, which is a part of an upper section of the gastrointestinal tract. It supplies swallowed food along with its length.

Disorders of the Human Digestive System

Vomiting : It is the ejection of stomach contents through the mouth.

Diarrhoea : It is the abnormal watery bowel movement. Prolonged diarrhoea eventually leads to dehydration.

Constipation : A condition in which the faeces are clutched within the rectum due to an irregular bowel movement.

Indigestion : A pain or discomfort in the stomach which is caused when food is not digested properly, resulting in the feeling of fullness. Indigestion is mainly caused due to inadequate enzyme secretion, food poisoning, anxiety, overeating and eating spicy foods.

Also Read: Difference between trachea and oesophagus

Functions of the Human Digestive System

Digestion and absorption are the two main functions of the digestive system.

Digestion is necessary for breaking down food particles into nutrients that are used by the body as an energy source, cell repair and growth.

Food and drink need to be converted into smaller molecules of nutrients before it is absorbed by the blood and carried to the cells throughout the body. The body breaks the nutrients present in the drinks and food into carbohydrates, vitamins, fats and proteins.

Human Digestive System Notes

The human digestive system breaks down food to release energy essential for the body to carry out its activities.
The process of digestion takes place in 6 major steps.
The food is ingested by the alimentary canal and is propelled through the body for further processing.
The autonomous nervous system controls the peristalsis, contraction and relaxation of muscles within the alimentary canal wall.
The food is passed to the small intestine where it is digested, and the nutrients are absorbed.
Water, electrolytes and vitamins are absorbed by the large intestine and the waste is defecated.

Frequently Asked Questions

Deduce the function of the human digestive system..

The digestive system consists of the alimentary canal and the accessory organs. Their main function is to break down the ingested food into its components and produce vital nutrients and energy required to sustain life.

What are accessory organs?

Accessory organs are organs which are not part of the digestive system; however, they aid in the digestion process by performing many secondary functions. The main accessory organs of the digestive system are the tongue, liver, pancreas and gall bladder.

Outline the process of digestion, step by step.

The process of digestion involves the following steps, namely:

List out the parts of the digestive system.

Mouth & Buccal Cavity

Explain the role of the tongue as an accessory organ.

The tongue is not a part of the digestive system, but it provides support functions such as moving and manipulating the food within the buccal cavity. Furthermore, moistening food also helps to swallow and pass through the oesophagus without much resistance.

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Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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M03 Virtual Labs-Digestive System Part 2

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PDF 14.7
Digestive System Case Study MODULE 14: ANATOMY & PHYSIOLOGY CASE STUDY #7 Isabel's Case: The Burn in My Chest Isabel is a young Latina woman, age 24, who loves to cook. Her mom taught her many of the traditional spicy Hispanic dishes her family ate while growing up. Recently Isabel got married and moved into a new home with her husband.
PDF 14.7
Digestive System Case Study MODULE 14: ANATOMY & PHYSIOLOGY CASE STUDY #7 Isabel's Case: The Burn in My Chest Isabel is a young Latina woman, age 24, who loves to cook. Her mom taught her many of the traditional spicy Hispanic dishes her family ate while growing up. But recently Isabel got married and moved into a new home with her husband ...
Digestive System Case studies Flashcards
Study with Quizlet and memorize flashcards containing terms like Compare the test results to normal (nl) and indicate by arrows (up or down) how any lab values deviate from typical., A "fruity acetone combined with alcohol" smell was detected in Mr. Boulard's breath and in his urine. Which substance is producing the "fruity acetone" smell?, Where in the body are ketone bodies produced? What ...
digestive case study Flashcards
Study with Quizlet and memorize flashcards containing terms like As Dr. Lorraine is listening to Mr. Volpe's complaints she automatically visualizes the organs in the epigastric region that are the potential source of his problems. Where is the epigastric region and what organs associated with digestion are located in that area?, The structures in the epigastric region share a common nerve ...
Chapter 15 Answers: Digestive System
Digestion is a form of catabolism, in which food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs in the organs of the digestive system that make up the gastrointestinal tract. Self-marking. Identify two organ systems that control the process of digestion by the digestive system.
Case Study #7
View Lab - Case Study #7 - Digestive System.docx from BIOL 220 at University of Richmond. BIOL 220 Case Study #7: Digestive System Name _Megan Thompson_ Directions: Provide TYPED, concise responses. ... Answer D QUESTION 667 A company with a single AWS account runs its internet. document.
A&P
A&P - Lab 9 - Digestive System and Nutrition Case Studies. Term. 1 / 25. Which substance produces the "fruity acetone" smell? Click the card to flip 👆. Definition. 1 / 25.
23.1 Overview of the Digestive System
Accessory digestive organs, despite their name, are critical to the function of the digestive system. Alimentary Canal Organs Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = "to nourish") is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length ...
9: Module 7- The Digestive System
9.1: Introduction to the Digestive System; 9.2: Overview of the Digestive System; 9.3: Digestive System Processes and Regulation; 9.4: The Mouth, Pharynx, and Esophagus; 9.5: The Stomach; 9.6: The Small and Large Intestines; 9.7: Accessory Organs in Digestion- The Liver, Pancreas, and Gallbladder; 9.8: Chemical Digestion and Absorption- A ...
18.1: Case Study: Food Processing
This page titled 18.1: Case Study: Food Processing is shared under a CK-12 license and was authored, remixed, and/or curated by Suzanne Wakim & Mandeep Grewal via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. Rania can't eat gluten, because she has celiac ...
Chapter 15 Answers: Digestive System
178 Chapter 15 Answers: Digestive System 15.2 Introduction to the Digestive System: Review Questions and Answers. ... 15.8 Case Study Conclusion and Chapter Summary: Review Questions and Answers. Self-marking; Explain how the accessory organs of digestion interact with the GI tract.
Digestive System
Chapter 17: Digestive System In this Chapter: Textbook Resources. Study on the Fly; Biology and A&P Prep Sites; Get Body Smart; Essential Study Partner; Lab Exercises; Atlases; Case Studies; Student Study Outlines ... Case Studies; Student Study Outlines; Supplemental Lab Exercises (Hole) Boxed Readings;
Chapter 7 Answers: Introduction to the Human Body
7.9 Case Study Conclusion: Review Questions and Answers. Compare and contrast tissues and organs. Answers may vary. Sample answer: Tissues and organs are both units within the body that carry out a particular function, and are composed of cells. Tissues, however, consist of cells that have similar properties, while organs are made up of two or ...
23.1 Overview of the Digestive System
Accessory digestive organs, despite their name, are critical to the function of the digestive system. Alimentary Canal Organs Also called the gastrointestinal (GI) tract or gut, the alimentary canal (aliment- = "to nourish") is a one-way tube about 7.62 meters (25 feet) in length during life and closer to 10.67 meters (35 feet) in length ...
Digestive System
The digestive system, with the help of the circulatory system, acts like a gigantic "meals on wheels," providing nourishment to over a hundred trillion "customer" cells in the body. It also has its own quality control and waste disposal system. The digestive system provides the body with water, electrolytes, andother nutrients.
Chapter 17 Answers
An accessory organ of the digestive system. B. Part of the upper GI tract. C. Part of the lower GI tract. D. The longitudinal muscle. Review Answers. The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining food waste. The three main functions of the digestive system are digestion, absorption ...
CHAPTER 7: DIGESTIVE SYSTEM Case 7-2 LOCATION:
Operations Management questions and answers; CHAPTER 7: DIGESTIVE SYSTEM Case 7-2 LOCATION: Inpatient, Hospital PATIENT: Sara Milton ATTENDING/ADMIT PHYSICIAN: Alma Naraquist, MD SURGEON: Larry P. Friendly, MD PREOPERATIVE DIAGNOSIS: Abdominal sepsis. POSTOPERATIVE DIAGNOSIS: Myeloproliferative disorder; sigmoid perforation,
Solved Module 7 Case Study 4: Digestive System Ch. 27
Anatomy and Physiology questions and answers. Module 7 Case Study 4: Digestive System Ch. 27 Reproductive Case History: A 26-year-old female complained of severe, dull, aching pain, and cramping in the lower abdomen. There were no other physical findings. A laparoscopy revealed the presence of ectopic endometrial tissue on the uterine wall and ...
Chapter 11: The Digestive System Flashcards
a long, continuous rube comprising the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. ingestion. the taking in of nutrients through the mouth. digestion. the mechanical and chemical breakdown of food for use by body cells. absorption.
Human Digestive System
The digestive system of the human body is the sum of the gastrointestinal tract (GIT; also called alimentary canal) and accessory organs (tongue, liver, pancreas, etc.). These two parts together help in the digestion process. The alimentary canal is the long tube through which the food that we eat is passed.
Solved Digestive System: This is a two-part case study due
Digestive System: This is a two-part case study due to the many questions. This first part contains Qs1-4 and PT2 will contain Qs5-7. Thank you! :) Q1) Does the bowel cease to function following abdominal surgery? What is the term for this? Q2) What causes bowel sounds heard through the abdominal wall with or without a stethoscope?
M03 Virtual Labs-Digestive System Part 2 (docx)
Question 1 1 / 1 pts Name the organs that are part of the alimentary canal of the digestive system. List the organs in order from beginning to end, starting with the mouth. Your Answer: 1. Mouth 2. pharynx 3. esophagus 4. stomach 5. duodenum 6. jejunum 7. cecum 8. ascending colon 9. transverse colon 9. sigmoid colon 10. rectum 11. anal canal 12. anus Question 2 1 / 1 pts Name the organs that ...
Unit 7: The digestive system review Flashcards
Muscles of mastication. 7 terms. darya_de_wit. Preview. Study with Quizlet and memorize flashcards containing terms like What is the function of the digestive system, What is the chemical digestion, What is physical digestion and more.
Weekend Edition Sunday for April 7, 2024 : NPR
The Apple Pay app on an iPhone in New York. Consumers tend to spend about 10% more when they adopt mobile contactless payment methods, a researcher says.
Grade 7
Rectum. Part of the large intestine where waste material is compressed into solid forms. anus. Muscular opening at the end of the rectum where waste material is eliminated from the body. Study with Quizlet and memorize flashcards containing terms like Path of Food, Functions of Digestive System, Digestion and more.

23.1 Overview of the Digestive System

Digestive System Organs

Alimentary Canal Organs

Accessory Structures

Histology of the Alimentary Canal

Nerve Supply

Blood Supply

The Peritoneum

Disorders of the...

Interactive Link

18.1: Case Study: Food Processing

Case Study: Please Don’t Pass the Bread

Chapter Overview: Digestive System

Attributions

178 Chapter 15 Answers: Digestive System

15.3 Digestion and Absorption: Review Questions and Answers

15.4 Upper Gastrointestinal Tract: Review Questions and Answers

15.5 Lower Gastrointestinal Tract: Review Questions and Answers

15.6 Accessory Organs of Digestion: Review Questions and Answers

15.7 Disorders of the Gastrointestinal Tract: Review Questions and Answers

15.8 Case Study Conclusion and Chapter Summary: Review Questions and Answers

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Chapter 7 Answers: Introduction to the Human Body

7.3 Cells and Tissues: Review Questions and Answers

7.4 Tissues: Review Questions and Answers

7.5 Human Organs and Organ Systems: Review Questions and Answers

7.6 Human Body Cavities: Review Questions and Answers

7.7 Interactions of Organ Systems: Review Questions and Answers

7.8 Homeostasis and Feedback: Review Questions and Answers

7.9 Case Study Conclusion: Review Questions and Answers

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23.1 Overview of the Digestive System

Digestive System Organs

Alimentary Canal Organs

Accessory Structures

Histology of the Alimentary Canal

Nerve Supply

Blood Supply

The Peritoneum

External Website

Chapter Review

Interactive Link Questions

Review Questions

Human Digestive System

Table of Contents

Large Intestine

The Human Digestive System

Diagram Of The Human Digestive System

Parts of the Human Digestive System

Disorders of the Human Digestive System

Functions of the Human Digestive System

Human Digestive System Notes

Frequently Asked Questions

What are accessory organs?

Outline the process of digestion, step by step.

List out the parts of the digestive system.

Explain the role of the tongue as an accessory organ.

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M03 Virtual Labs-Digestive System Part 2

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Environment

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The Cherokee community in North Carolina celebrates a high school championship win

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