The Digestive System and Digestive Tract Diseases

The digestive tract (also called the gastrointestinal tract or GI tract) is a hollow tube of about 30 feet (9 meters) in length that extends through the body from the mouth to the anus. As food travels along the digestive tract it’s gradually broken down by digestive enzymes. The food is eventually converted into particles that are small enough to be absorbed by the blood and lymph vessels in the wall of the digestive tract. The blood then distributes the food particles to cells throughout the body.

When food is swallowed it travels down the esophagus, which transports the food to the stomach. The food moves from the stomach into the small intestine. Digestion is finished in the small intestine. The digested food is then absorbed. The remaining material passes from the small intestine into the large intestine, where water and some salts are absorbed. The left over material (feces) is stored in a chamber at the end of the large intestine called the rectum until the rectum is full.

The liver and pancreas help digestion in the digestive tract. The liver produces a green fluid called bile, which emulsifies fats in the small intestine, breaking them up into small droplets that digestive enzymes can attack more easily. The pancreas makes digestive enzymes and sends them into the small intestine.

1. The salivary glands in the mouth generally make between 0.5 and 2 liters of saliva each day.

2. We make more saliva when we see, smell, taste or even think about food. All these factors make our mouth “water”.

3. Saliva contains an enzyme called salivary amylase (or ptyalin) which begins the digestion of starch. Chewing also helps break up food.

4. Saliva contains several antimicrobial enzymes, including lysozyme. Lysozyme damages the cell walls of bacteria, killing them.

5. Saliva flow helps remove trapped food in the mouth and also helps to neutralize acids, reducing the chance of cavities.

6. Chemicals in saliva remineralize tooth enamel, strengthening it after acids have removed minerals from the enamel.

7. Saliva also lubricates food, making it easy to swallow.

8. Xerostomia, or dry mouth, is a condition in which little or no saliva is made. It’s sometimes known as “cotton mouth”.

9. Xerostomia makes speaking and swallowing difficult and leads to increased tooth decay. It also causes halitosis (bad breath).

10. There are many causes of xerostomia. Some of these causes are dehydration, anxiety, certain medications and drugs, alcohol, radiation therapy to the head or neck, and breathing through the mouth instead of the nose. Aging also results in reduced saliva production, although this may be due to the fact that older people often take more medications than younger people.

11. Sjogren’s syndrome is an autoimmune disease in which the body’s immune system destroys the glands that make saliva and tears, resulting in xerostomia.

12. Other diseases may include xerostomia as a symptom. These diseases include diabetes mellitus, rheumatoid arthritis, hypertension (high blood pressure) and thyroid problems.

1. The function of the esophagus is to transport the swallowed food to the stomach.

2. At the end of the esophagus is a circular muscle called the lower esophageal sphincter (LES), also known as the cardiac sphincter. This muscle acts like a valve and normally closes off the entrance to the stomach when the stomach is digesting food.

3. In some people the lower esophageal sphincter doesn’t close the exit of the esophagus properly. This allows the acidic stomach contents to move upwards into the stomach, producing a burning sensation known as heartburn. People with this condition are said to suffer from acid reflux, or gastroesophageal reflux disease (GERD).

4. Some foods and drinks can also affect the function of the lower esophageal sphincter and trigger the stomach contents to enter the esophagus in certain people. Foods that may have this effect include fatty foods, spicy foods, onions, garlic, peppermint, tomatoes, citrus fruits, chocolate, caffeine, coffee and alcohol.

5. Smoking also weakens the lower esophageal sphincter and can produce heartburn.

6. A very full stomach or being pregnant or overweight can put pressure on the stomach and the lower esophageal sphincter, forcing stomach contents into the esophagus and causing heartburn.

7. Peristalsis is a series of wave-like muscle contractions in the walls of the digestive tract that propel food down the esophagus, stomach and intestines.

1. The stomach is a hollow sac which has a volume of about 1 liter when empty. It can expand to about 4 liters when it's full.

2. The stomach lining produces hydrochloric acid, which produces a pH of 1 to 3 in the stomach cavity. The pH scales runs from 1 to 14, with 1 being the most acidic pH and 14 being the most basic (alkaline) pH.

3. The stomach lining also produces an inactive enzyme called pepsinogen. In the stomach cavity hydrochloric acid converts pepsinogen into pepsin, an enzyme which partially digests proteins. The acid also kills many (but not all) bacteria in the stomach.

4. In addition, the stomach lining produces a mucus layer which protects the stomach from damage by pepsin and hydrochloric acid.

5. One bacterium can hide in the mucus, where it is protected from the acidic stomach contents. This bacterium is called Helicobacter pylori, or H. pylori. In some people this bacterium causes no apparent problems, but it others an H. pylori infection can result in painful inflammation of the stomach lining (gastritis) and sores called ulcers.

6. Indigestion, or dyspepsia, is a term that refers to abdominal discomfort. Symptoms may include pain, bloating and nausea. Indigestion is usually not serious and is short-lived. Indigestion may be caused by overeating or eating too fast, drinking too many carbonated drinks, anxiety, certain medications and many of the same foods that can cause heartburn.

7. Indigestion that lasts for a long time or occurs repeatedly requires medical treatment. Indigestion with additional symptoms such as shortness of breath, chest pain or pressure, arm pain and sweating requires immediate medical attention, since these can be symptoms of a heart attack. Indigestion accompanied by vomiting, a yellow color in the skin or eyes (jaundice), black feces (which may be due to blood in the feces) or weight loss also requires medical attention.

8. At the bottom of the stomach is a circular muscle called the pyloric sphincter. This sphincter allows the partially digested food from the stomach, known as chyme, to gradually enter the small intestine.

1. The small intestine is about 20 feet (6 meters) long and is the longest part of the digestive tract. It has three sections called the duodenum, the jejunum and the ileum.

2. The small intestine is folded into loops in order to fit into the abdominal cavity.

3. Bile made by the liver is stored in the gall bladder until it’s needed. Bile is sent to the small intestine when fat is eaten to help break up the fat.

4. The pancreas sends several digestive enzymes into the small intestine, including pancreatic amylase, which digests starch, and lipase, which digests fats.

5. The pancreas also sends trypsinogen to the stomach. The inactive trypsin is turned into active trypsin in the small intestine. Trypsin then digests proteins.

6. The pancreatic enzymes are transported to the small intestine in a basic fluid, which helps neutralize the acidic material from the stomach.

7. Glands in the lining of the small intestine secrete additional enzymes to finish digesting the food.

8. The lining of the small intestine contains tiny folds called villi. The villi increase the surface area available for absorption of digested food.

1. In people with celiac disease the villi in the small intestine are damaged or destroyed, so insufficient nutrients can be absorbed.

2. Celiac disease develops in people who are intolerant to gluten, a protein found in certain grains, including wheat, rye and barley. Gluten is also used as a food additive.

3. Gluten can cause problems outside the digestive tract as well as in the digestive tract in sensitive people.

4. In most people with celiac disease, the villi will heal and regrow if a gluten-free diet is followed.

5. Crohn’s disease is a condition in which part of the digestive tract is inflamed. Any part of the digestive tract may be affected, but the most commonly affected sites are the small and large intestine, especially the ileum. Crohn’s disease is classified as a type of inflammatory bowel disease. "Bowel" is an alternate name for intestine. The inflamed areas may be located in patches which are surrounded by healthy tissue.

6. Symptoms of Crohn’s disease include abdominal pain and diarrhea, which may be bloody. Ulcers may be present. There may also be nausea, vomiting and weight loss.

7. People with Crohn’s disease may experience flare-ups, when their symptoms are present, alternating with periods of remission, when symptoms are weaker.

8. The cause of Crohn’s disease is not known, but scientists do know that the immune system reacts abnormally in the digestive tract during Crohn’s disease.

1. The cecum is a pouch that is located where the last section of the small intestine (the ileum) connects to the large intestine, on the right side of the abdomen (from the body owner's point of view).

2. The appendix is a close-ended, worm-like tube extending from the cecum.

3. Scientists have assumed for a long time that the appendix has no function in modern humans, although it is believed to have been used in our distant ancestors to help break down plant matter.

4. Some scientists have suggested that the appendix plays a role in our immune system, which is the system that fights disease.

5. Inflammation of the appendix is called appendicitis. Appendicitis is due to a bacterial infection inside the appendix, which causes the appendix to swell and become painful.

6. Scientists are not sure how the appendix infection arises. One idea is that bits of stool (feces) from the large intestine block the opening to the appendix. Bacteria in the stool may infect the appendix.

7. Another idea is that mucus made by the appendix blocks the opening of the appendix instead of flowing into the large intestine. The opening of the appendix may also be blocked by food material.

8. A third idea is that bacteria from a stomach or small intestine infection enter the appendix and multiply.

9. The membrane that lines the abdominal cavity and covers the organs in the cavity is called the peritoneum. If a swollen and infected appendix bursts, the peritoneum may become inflamed. This is an extremely serious condition called peritonitis.

10. Most people with appendicitis are treated by removal of the appendix.

11. People without an appendix appear to live a normal life.

1. The large intestine is about 5 feet long (1.5 meters). Although the large intestine is shorter than the small intestine, it’s also wider.

2. The parts of the large intestine, starting from where the small intestine connects to the large intestine, are the cecum, the colon (which is the longest part and has several sections) and the rectum.

3. Scientists believe that between 500 and 1000 different species of bacteria live in the large intestine. Some yeasts are also normal inhabitants of the large intestine.

4. Scientists estimate that there are at least ten times more bacterial cells in our body than there are human cells. These bacteria live on the surface of the body and in body passageways, but the majority are found in the large intestine. Bacterial cells are much smaller than human cells.

5. Most of the bacteria in the large intestine are harmless, but some are very helpful. Some of the bacteria produce vitamin K, which we absorb and use in the blood clotting process. Some produce B vitamins, including biotin, which we also absorb, although it is unclear how significant this absorption is with respect to our daily requirement for vitamins.

6. Large intestine bacteria may also decrease the level of pathogenic (disease-causing) organisms in the intestine.

7. Some intestinal bacteria ferment soluble fiber into short-chain fatty acids.

8. The short-chain fatty acids (SCFA) have been found to have a number of health benefits, including helping to maintain blood glucose levels, reducing the level of LDL cholesterol (the “bad” cholesterol) in the body and stimulating the activity of the immune system.

9. In the large intestine, excess water is removed from the intestinal contents and absorbed into the bloodstream. If too much water is removed, a person will experience constipation. If too little water is removed, the person will experience diarrhea.

1. Ulcerative colitis is a type of inflammatory bowel disease that is similar to Crohn’s disease but affects only the large intestine. The linings of both the colon and the rectum may become inflamed and develop ulcers.

2. In ulcerative colitis the surface layer of the large intestine lining is inflamed, while Crohn’s disease causes both surface and deeper damage. Another difference between the two types of inflammatory bowel disease is the fact that the inflammation in ulcerative colitis is generally continuous instead of occurring in patches.

3. People suffering from ulcerative colitis may experience the same symptoms as people with Crohn’s disease - pain, diarrhea, bleeding from the rectum, nausea and weight loss. They may also experience alternating flare-ups and remissions.

4. The cause of ulcerative colitis is not known, but the immune system reacts abnormally in the large intestine during colitis just as it does during Crohn’s disease.

1. Irritable bowel syndrome (IBS) involves abdominal pain accompanied by diarrhea (in diarrhea-predominant IBS, or IBS-D), constipation (in constipation-predominant IBS, or IBS-C) or alternating diarrhea and constipation.

2. There is no damage to the large intestine in irritable bowel syndrome. Instead, the colon is unusually sensitive to certain triggers, which are often substances in the diet. The triggers may be different in different people. People suffering from IBS need to discover their personal triggers and then avoid them.

3. Common IBS triggers include fatty foods, sorbitol, concentrated fructose, caffeinated or carbonated beverages and alcohol. Dairy also frequently causes IBS, although some people find that fermented dairy is safe to eat. Some people with diarrhea-predominant IBS find that raw vegetables and too much insoluble fiber trigger an IBS attack, while cooked vegetables and soluble fiber do not. People with constipation-predominant IBS may find that insoluble fiber helps their condition.

4. People with irritable bowel syndrome should also check that they do not have conditions that can have similar symptoms to IBS, such as celiac disease, Crohn’s disease and ulcerative colitis.

1. The rectum is the last five to eight inches of the large intestine.

2. The colon sends its contents into the rectum. The rectum stretches as it fills up.

3. The walls of the rectum contain stretch receptors. When the rectum has expanded by a certain amount, the stretch receptors are stimulated and send a message to the brain, which gives us the sensation that we need to defecate (release feces from the body). Feces is then sent into the short anal canal and then out of the body through the anus.

4. Hemorrhoids, sometimes known as piles, are swollen veins in the anal canal (internal hemorrhoids) or close to the anus (external hemorrhoids). Hemorrhoids may be painful or itchy and may bleed.

5. Large hemorrhoids may protrude through the anus.

6. It is not always clear why hemorrhoids develop. Some possible causes are straining during defecation and any condition that puts pressure on the area, such as being overweight or pregnant. Aging may weaken the tissue that supports the veins in the anal canal and increase the likelihood of hemorrhoid development. Genetics may also play a role.

7. The time between ingestion of food in the mouth and release of the undigested food in the feces is generally between 24 and 72 hours.