Created by CK-12 Foundation/Adapted by Christine Miller
Case Study Conclusion: Please Don’t Pass the Bread
The bread above may or may not look appetizing to you, but for people with celiac disease, it is certainly off limits. Bread and pasta are traditionally made with wheat, which contains proteins called . As you learned in the beginning of the chapter, even trace amounts of gluten can damage the digestive system of people with celiac disease. When Angela and Saloni met for lunch, Angela chose a restaurant that she knew could provide her with gluten-free food because she has this disease.
When people with celiac disease eat gluten, it causes an autoimmune reaction that results in inflammation and flattening of the of the . What do you think happens if the villi are inflamed and flattened? Think about what you have learned about the functions of the villi and small intestine. The small intestine is where most chemical digestion and absorption of nutrients occurs in the body. The villi increase the surface area in the small intestine to maximize the digestion of food and absorption of nutrients into the blood and lymph. If the villi are inflamed and flattened, there is less surface area where digestion and absorption can occur. Therefore, damage from celiac disease can result in an inadequate absorption of nutrients called malabsorption.
explains why there can be so many different types of symptoms of celiac disease, ranging from diarrhea and other forms of digestive distress, to , nutritional deficiencies, skin rashes, and bone pain, depression and anxiety, and rarer — but potentially serious — complications, such as . Our bodies need to digest and absorb adequate amounts of nutrients in order to function properly and stay healthy. Lack of nutrients can affect and damage cells, tissues, and organs throughout the body, sometimes seriously and irreversibly. A person with celiac disease can limit and often heal intestinal damage just by not eating gluten. In fact, eliminating all gluten from the diet is the main treatment for celiac disease. In some people with celiac disease, a gluten-free diet may not be enough, and steroids and other medications may be used to reduce the inflammation in the small intestine.
Celiac disease is an autoimmune disorder in which the body’s attacks its own tissues. It is thought to be caused by the presence of particular genes in combination with exposure to gluten. What are some other autoimmune disorders that you read about in this chapter that affect the digestive system? The two main inflammatory bowel diseases, Crohn’s disease and ulcerative colitis, are both due to the body’s immune system attacking the digestive system, resulting in inflammation. Crohn’s disease can affect any part of the GI tract, most commonly the ileum of the small intestine, while ulcerative colitis mainly affects the colon and rectum. Similar to celiac disease, treatments for these diseases also focus on reducing GI tract damage through lifestyle changes and medications.
Gluten is clearly dangerous for people with celiac disease, but should people who do not have celiac disease or other diagnosed medical problem with gluten also eliminate gluten from their diet? Many medical experts say no, because gluten-free diets are so restrictive, they may cause nutritional deficiencies without providing any proven health benefits. They can also be expensive and, as Saloni’s cousin found out, difficult to maintain, given that gluten is present in so many foods. It is estimated that only one per cent of the population has celiac disease. Most people should enjoy a varied diet and consult with their doctor if they are concerned about celiac disease, other types of gluten intolerance, or food allergies.
Watch this TED-Ed video “What’s the big deal with gluten? – William D. Chey” to learn more:
What’s the big deal with gluten? – William D. Chey, TED-Ed, 2015.
In this chapter, you learned about the digestive system, which allows the body to obtain needed nutrients from food. Specifically, you learned that:
- The consists of organs that break down food, absorb its nutrients, and expel any remaining food waste.
- Most digestive organs form a long, continuous tube through which food passes, called the . It starts at the mouth, which is followed by the pharynx, esophagus, stomach, small intestine, and large intestine.
- Organs of the GI tract have walls that consist of several tissue layers that enable them to carry out digestion and/or absorption. For example, the inner 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 to move food through the GI tract.
- Digestion is a form of , in which food is broken down into small molecules that the body can absorb and use for energy, growth, and repair. Digestion occurs when food moves through the GI tract. The digestive process is controlled by both hormones and nerves.
- is a physical process in which food is broken into smaller pieces without becoming chemically changed. It occurs mainly in the mouth and stomach.
- is a chemical process in which macromolecules — including carbohydrates, proteins, lipids, and nucleic acids — in food are changed 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. Chemical digestion requires digestive enzymes. Gut flora carry out additional chemical digestion.
- occurs when the simple nutrient molecules that result from digestion are absorbed into blood or lymph. They are then circulated through the body.
- Organs of the include the mouth, pharynx, esophagus, and stomach.
- The is the first organ of the GI tract. It has several structures that are specialized for digestion, including , , and . Both mechanical digestion and chemical digestion of carbohydrates and fats begin in the mouth.
- The and move food from the mouth to the stomach but are not directly involved in the process of digestion or absorption. Food moves through the esophagus by peristalsis.
- Mechanical and chemical digestion continue in the . 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 .
- The includes the small intestine and large intestine. The small intestine is where most chemical digestion and virtually all absorption of nutrients occur. The large intestine contains huge numbers of beneficial bacteria, and removes water and salts from food waste before it is eliminated.
- The small intestine consists of three parts: the duodenum, jejunum, and ileum. All three parts of the small intestine are lined with mucosa that is very wrinkled and covered with villi and microvilli, giving the small intestine a huge surface area for digestion and absorption.
- The secretes digestive enzymes and also receives bile from the liver or gallbladder and digestive enzymes and bicarbonate from the pancreas. These digestive substances neutralize acidic chyme and allow for the chemical digestion of carbohydrates, proteins, lipids, and nucleic acids in the duodenum.
- The carries out most of the absorption of nutrients in the small intestine, including the absorption of simple sugars, amino acids, fatty acids, and many vitamins.
- The carries out any remaining digestion and absorption of nutrients, but its main function is to absorb vitamin B12 and bile salts.
- The large intestine consists of the colon (which in turn includes the , ascending , transverse colon, descending colon, and sigmoid colon), rectum, and anus. The is attached to the cecum of the colon.
- The main function of the large intestine is to remove water and salts from chyme for recycling within the body and eliminating the remaining solid feces from the body through the anus. The large intestine is also the site where trillions of bacteria help digest certain compounds, produce vitamins, stimulate the immune system, and break down toxins, among other important functions.
- Accessory organs of digestion are organs that secrete substances needed for the chemical digestion of food, but through which food does not actually pass as it is digested. The accessory organs include the liver, gallbladder, and pancreas. These organs secrete or store substances that are carried to the duodenum of the small intestine as needed for digestion.
- The is a large organ in the abdomen that is divided into lobes and smaller lobules, which consist of metabolic cells called hepatic cells, or hepatocytes. The liver receives oxygen in blood from the aorta through the hepatic artery. It receives nutrients in blood from the GI tract and wastes in blood from the spleen through the portal vein.
- The main digestive function of the liver is the production of the alkaline liquid called . Bile is carried directly to the duodenum by the common bile duct or to the gallbladder first for storage. Bile neutralizes acidic chyme that enters the duodenum from the stomach and also emulsifies fat globules into smaller particles (micelles) that are easier to digest chemically.
- Other vital functions of the liver include regulating blood sugar levels by storing excess sugar as glycogen; storing many vitamins and minerals; synthesizing numerous proteins and lipids; and breaking down waste products and toxic substances.
- The is a small pouch-like organ near the liver. It stores and concentrates bile from the liver until it is needed in the duodenum to neutralize chyme and help digest lipids.
- The is a glandular organ that secretes both endocrine hormones and digestive enzymes. As an endocrine gland, the pancreas secretes and to regulate blood sugar. As a digestive organ, the pancreas secretes digestive enzymes into the duodenum through ducts. Pancreatic digestive include amylase (starches); trypsin and chymotrypsin (proteins); lipase (lipids); and ribonucleases and deoxyribonucleases (RNA and DNA).
- is a collection of inflammatory conditions primarily affecting the intestines. The diseases involve the immune system attacking the GI tract, and they have multiple genetic and environmental causes. Typical symptoms include abdominal pain and diarrhea, which show a pattern of repeated flare-ups interrupted by periods of remission. Lifestyle changes and medications may control flare-ups and extend remission. Surgery is sometimes required.
- The two principal inflammatory bowel diseases are Crohn’s disease and ulcerative colitis. may affect any part of the GI tract from the mouth to the anus, among other body tissues. affects the colon and/or rectum.
- Some people have little pouches, called diverticula, in the lining of their large intestine, a condition called . People with diverticulosis may develop , 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.
- A is a sore in the lining of the stomach (gastric ulcer) or duodenum (duodenal ulcer). The most common cause is infection with the bacterium Helicobacter pylori. such as aspirin can also cause peptic ulcers, and some lifestyle factors may play contributing roles. Antibiotics and acid reducers are typically prescribed. Surgery is not often needed.
- , or infectious diarrhea, is an acute and usually self-limiting infection of the GI tract by pathogens, most often viruses. Symptoms typically include diarrhea, vomiting, and/or abdominal pain. Treatment includes replacing lost fluids. Antibiotics are not usually effective.
- is a type of gastroenteritis caused by infection of the GI tract with the protozoa parasite Giardia lamblia. It may cause malnutrition. Generally self-limiting, severe or long-lasting cases may require antibiotics.
As you have learned, the process of digestion, in which food is broken down and nutrients are absorbed by the body, also involves the of solid wastes. Elimination of waste is also called excretion. Some of the organs of the digestive system, such as the liver and large intestine, are also considered part of the excretory system. Read the next chapter to learn more about the excretory system and how wastes are eliminated from our bodies.
- Explain how the accessory organs of digestion interact with 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?
- Discuss whether digestion occurs in the large intestine.
- Lipids are digested at different points in the digestive system. Describe how lipids are digested at two of these points.
- Describe two different functions of stomach acid.
- Name and describe the location and function of three of the valves of the GI tract.
- What is the name of the rhythmic muscle contractions that move food through the GI tract?
- What are the major roles of the upper GI tract?
- What is the physiological cause of heartburn?
- What are two ways in which the tongue participates in digestion?
- Where is the epiglottis located? If the epiglottis were to not close properly, what might happen?
TED-Ed. (2015, June 2). What’s the big deal with gluten? – William D. Chey. YouTube. https://www.youtube.com/watch?v=uEM2iDT-VAk&feature=youtu.be
A substance present in cereal grains, especially wheat, that is responsible for the elastic texture of dough. A mixture of two proteins, it causes illness in people with celiac disease.
A microscopic, finger-like projections in a mucous membrane that form a large surface area for absorption.
A long, narrow, tube-like organ of the digestive system where most chemical digestion of food and virtually all absorption of nutrients take place.
The imperfect absorption of food material by the small intestine.
A condition in which you don't have enough healthy red blood cells to carry adequate oxygen to the body's tissues resulting in symptoms including weakness and fatigue.
A medical condition in which the bones become brittle and fragile from loss of tissue, typically as a result of hormonal changes, or deficiency of calcium or vitamin D.
A group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body.
The body system in humans and other animals that protects the organism by distinguishing foreign tissue and neutralizing potentially pathogenic organisms or substances.
A body system including a series of hollow organs joined in a long, twisting tube from the mouth to the anus. The hollow organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system.
The organs of the digestive system through which food passes during digestion, including the mouth, pharynx, esophagus, stomach, and small and large intestines.
The innermost tunic of the wall. It lines the lumen of the digestive tract. The mucosa consists of epithelium, an underlying loose connective tissue layer called lamina propria, and a thin layer of smooth muscle called the muscularis mucosa.
A distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines.
The breakdown of larger molecules into smaller ones.
The physical breakdown of chunks of food into smaller pieces by organs of the digestive system, for example chewing food.
Chemical breakdown of large, complex food molecules into smaller, simpler nutrient molecules that can be absorbed by blood or lymph. Usually involves a digestive enzyme.
Process in which substances such as nutrients pass into the blood or lymph.
The part of the gastrointestinal tract that includes the mouth, pharynx, esophagus, and stomach.
The opening in the lower part of the human face, surrounded by the lips, through which food is taken in and from which speech and other sounds are emitted.
One of many exocrine glands in the mouth that secrete saliva into the mouth through ducts.
The fleshy muscular organ in the mouth used for tasting, licking, swallowing, and articulating speech.
A hard structure, embedded in the jaws of the mouth, that functions in chewing. Made of a dentin and covered in enamel, the hardest tissue in the body.
Tubular organ that connects the mouth and nasal cavity with the larynx and through which air and food pass.
A long, narrow, tube-like digestive organ through which food passes from the pharynx to the stomach.
A sac-like organ of the digestive system between the esophagus and small intestine in which both mechanical and chemical digestion take place.
A thick, semi-liquid mixture that food in the gastrointestinal tract becomes by the time it leaves the stomach.
The part of the GI tract that includes the small and large intestines.
The first and shortest of three parts of the small intestine where most chemical digestion occurs.
One of three sections that make up the small intestine. The jejunum is located between the duodenum and the ileum.The jejunum makes up about two-fifths of the small intestine. The main function of the jejunum is absorption of important nutrients such as sugars, fatty acids, and amino acids.
The third portion of the small intestine, between the jejunum and the cecum.The ileum helps to further digest food coming from the stomach and other parts of the small intestine.
A pouch connected to the junction of the small and large intestines.
The main part of the large intestine between the small intestine and rectum where water and salts are removed from liquid food wastes to form feces.
A tube-shaped sac attached to and opening into the lower end of the large intestine in humans and some other mammals. Some of the functions of the appendix include maintaining gut flora and immune and lymphatic function.
An organ of digestion and excretion that secretes bile for lipid digestion and breaks down excess amino acids and toxins in the blood.
Fluid produced by the liver and stored in the gall bladder that is secreted into the small intestine to help digest lipids and neutralize acid from the stomach.
A sac-like organ that stores bile from the liver and secretes it into the duodenum of the small intestine as needed for digestion.
A long, flat gland that sits tucked behind the stomach in the upper abdomen. The pancreas produces enzymes that help digestion and hormones that help regulate the way your body processes sugar (glucose).
A hormone made by the pancreas that allows your body to use sugar (glucose) from carbohydrates in the food that you eat for energy or to store glucose for future use.
A peptide hormone, produced by alpha cells of the pancreas. It works to raise the concentration of glucose and fatty acids in the bloodstream, and is considered to be the main catabolic hormone of the body. It is also used as a medication to treat a number of health conditions.
Biological molecules that lower amount the energy required for a reaction to occur.
A type of disease in which the immune system attacks the intestines, causing diarrhea and abdominal pain; for example, Crohn’s disease or ulcerative colitis.
An inflammatory bowel disease that may affect any part of the gastrointestinal tract from the mouth to the anus.
An inflammatory bowel disease that causes ulcers (sores) in the colon and rectum.
A condition in which pouches called diverticula form in the wall of the large intestine.
A disease in which one or more pouches (diverticula) in the large intestine become infected and inflamed.
A sore that develops in the lining of the stomach or duodenum most often caused by infection with the bacterium Helicobacter pylori.
Non-steroidal anti-inflammatory drugs; ex. ibuprofen.
An acute and usually self-limiting infection of the gastrointestinal tract by pathogens; also known as infectious diarrhea.
A type of gastroenteritis caused by a single-celled protozoan parasite named Giardia lamblia that typically spreads through contaminated food or water via a fecal-oral route.
The process in which wastes pass out of the body.