DigestiveOverloadPrint - The Digestive System(Large images...

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The human digestive system or gastrointestinal tract is between 6.5 and 9 meters long. It consists of a tube 21 to 30 feet of specialized regions subdivided into the mouth, pharynx esophagus, stomach, small intestine, large intestine (or colon), rectum, and anus (see Fig. 1). Other glandular organs that have accessory roles in digestion and absorption include the salivary glands, liver, gallbladder and pancreas. For the most part, the entire length of the gastrointestinal tract has the same structure to its wall. The inside layer facing the gut lumen is the mucosa and it consists of a surface epithelial layer and an underlying layer of connective tissue. The mucosa is surrounded by a layer of connective tissue that is meshed with blood and lymph vessels. The next layer toward the outside of the tube is muscle tissue divided into two sublayers; it is smooth muscle arranged in longitudinal and circular directions. The outermost layer of the digestive tract is the connective tissue serosa. The digestive system has four basic functions which include motility, secretion, digestion and absorption. Motility involves contractions in the muscle layers that mix food material with secretions and move it forward through the gastrointestinal tract. The two common types of movement are peristalsis and segmentation. Peristalsis is when rings of circular muscles contract behind a mass of food material and relax in front of it to advance it forward. The forward motion expands the tube The Digestive Syst em (Large images at bottom)
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wall thus stimulating peristalsis further down the digestive system. The other type of movement is segmentation, which only happens in the intestines. Rings of smooth muscle contract and relax creating a back and forth movement that constantly mixes the contents of the lumen and forces them against the absorptive surface of the intestinal wall. The flow of material is controlled by sphincters that are rings of smooth striated muscle
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DigestiveOverloadPrint - The Digestive System(Large images...

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