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The wall of the large intestine is lined with simple columnar epithelium with invaginations. A mucus layer protects the large intestine from attacks from colonic commensal bacteria. High-quality clean proteins, including wild-caught tuna and salmon, grass-fed beef and lamb, and free-rage poultry and eggs are easy to digest — and will give your body essential nutrients and energy. The bile is stored between meals in the gallbladder. The appendix has also been shown to have a high concentration of lymphatic cells. Foods such as meat, eggs, and beans consist of large molecules of protein that must be digested by enzymes before they can be used to build and repair body tissues. Digestion is the process by which food and drink are broken down into their smallest parts so that the body can use them to build and nourish cells and to provide energy.
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The muscle of the organ produces a narrowing and then propels the narrowed portion slowly down the length of the organ. These waves of narrowing push the food and fluid in front of them through each hollow organ.
The first major muscle movement occurs when food or liquid is swallowed. Although we are able to start swallowing by choice, once the swallow begins, it becomes involuntary and proceeds under the control of the nerves.
The esophagus is the organ into which the swallowed food is pushed. It connects the throat above with the stomach below.
At the junction of the esophagus and stomach, there is a ringlike valve closing the passage between the two organs. However, as the food approaches the closed ring, the surrounding muscles relax and allow the food to pass.
The food then enters the stomach, which has three mechanical tasks to do. First, the stomach must store the swallowed food and liquid. This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach.
The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine. Several factors affect emptying of the stomach, including the nature of the food mainly its fat and protein content and the degree of muscle action of the emptying stomach and the next organ to receive the stomach contents the small intestine. As the food is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine, the contents of the intestine are mixed and pushed forward to allow further digestion.
Glands of the digestive system are crucial to the process of digestion. They produce both the juices that break down the food and the hormones that help to control the process. The glands that act first are in the mouth--the salivary glands.
Saliva produced by these glands contains an enzyme that begins to digest the starch from food into smaller molecules. The next set of digestive glands is in the stomach lining. They produce stomach acid and an enzyme that digests protein. One of the unsolved puzzles of the digestive system is why the acid juice of the stomach does not dissolve the tissue of the stomach itself. In most people, the stomach mucosa is able to resist the juice, although food and other tissues of the body cannot.
After the stomach empties the food and its juice into the small intestine, the juices of two other digestive organs mix with the food to continue the process of digestion. One of these organs is the pancreas. It produces a juice that contains a wide array of enzymes to break down the carbohydrates, fat, and protein in our food.
Other enzymes that are active in the process come from glands in the wall of the intestine or even a part of that wall. The liver produces yet another digestive juice--bile. The bile is stored between meals in the gallbladder. At mealtime, it is squeezed out of the gallbladder into the bile ducts to reach the intestine and mix with the fat in our food.
The bile acids dissolve the fat into the watery contents of the intestine, much like detergents that dissolve grease from a frying pan. After the fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine. How Is the Digestive Process Controlled?
A fascinating feature of the digestive system is that it contains its own regulators. The major hormones that control the functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine.
These hormones are released into the blood of the digestive tract, travel back to the heart and through the arteries, and return to the digestive system, where they stimulate digestive juices and cause organ movement.
The hormones that control digestion are gastrin, secretin, and cholecystokinin CCK: It is also necessary for the normal growth of the lining of the stomach, small intestine, and colon. It stimulates the stomach to produce pepsin, an enzyme that digests protein, and it also stimulates the liver to produce bile.
Two types of nerves help to control the action of the digestive system. Extrinsic outside nerves come to the digestive organs from the unconscious part of the brain or from the spinal cord.
They release a chemical called acetylcholine and another called adrenaline. Acetylcholine causes the muscle of the digestive organs to squeeze with more force and increase the "push" of food and juice through the digestive tract.
Acetylcholine also causes the stomach and pancreas to produce more digestive juice. Adrenaline relaxes the muscle of the stomach and intestine and decreases the flow of blood to these organs. Even more important, though, are the intrinsic inside nerves, which make up a very dense network embedded in the walls of the esophagus, stomach, small intestine, and colon. The intrinsic nerves are triggered to act when the walls of the hollow organs are stretched by food. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs.
Food and Nutrient Digestion - Overview. Diet and Nutrition Info. Other gas products formed are methane, hydrogen sulfide , ammonia, and various sulfur-containing mercaptans. Excess gas in the colon is eventually passed from the body by a process known as flatulence. Certain foods, such as beans, pork, onions, cabbage, and cauliflower, are known to increase gas production because of their high sulfur content. We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind.
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Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article. Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. The Editors of Encyclopaedia Britannica. Learn More in these related Britannica articles: Intestinal gas consists principally of swallowed air and partly of by-products of digestion.
When a person is in an upright position, gas diffuses to the uppermost portions of the colon. There it is compressed by the contraction of adjacent segments, giving rise to pain that…. Under normal atmospheric conditions, intestinal discomfort can be felt when air or gas collects in the intestines. Relief is obtained by expelling the gas…. Stomach , saclike expansion of the digestive system, between the esophagus and the small intestine; it is located in the anterior portion of the abdominal cavity in most vertebrates.
The stomach serves as a temporary receptacle for storage and mechanical distribution of food before it is passed into the intestine. Small intestine , a long, narrow, folded or coiled tube extending from the stomach to the large intestine; it is the region where most digestion and absorption of food takes place.
It is about 6. More About Intestinal gas 3 references found in Britannica articles Assorted References major reference In human digestive system: Intestinal gas cause of pain In digestive system disease: Intestinal gas role in intestinal squeeze In intestinal squeeze.
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