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.
- 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.