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The complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). [5] The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment.
Within its mucosa are millions of embedded gastric glands. Their secretions are vital to the functioning of the organ. Most of the digestion of food takes place in the small intestine which is the longest part of the GI tract. The largest part of the GI tract is the colon or large intestine.
The mucosa is the innermost layer of the gastrointestinal tract. It surrounds the cavity of the tract and comes into direct contact with digested food . The mucosa is made up of three layers: [1] The epithelium is the innermost layer. It is where most digestive, absorptive and secretory processes occur.
Mucus is released in the stomach and intestine, and serves to lubricate and protect the inner mucosa of the tract. It is composed of a specific family of glycoproteins termed mucins and is generally very viscous. Mucus is made by two types of specialized cells termed mucous cells in the stomach and goblet cells in the intestines. Signals for ...
The intestinal epithelium is the single cell layer that forms the luminal surface (lining) of both the small and large intestine (colon) of the gastrointestinal tract. Composed of simple columnar epithelium its main functions are absorption, and secretion. Useful substances are absorbed into the body, and the entry of harmful substances is ...
Egestion (Excretion): Removal of undigested materials from the digestive tract through defecation. Underlying the process is muscle movement throughout the system through swallowing and peristalsis. Each step in digestion requires energy, and thus imposes an "overhead charge" on the energy made available from absorbed substances.
The biliary tract can also serve as a reservoir for intestinal tract infections. Since the biliary tract is an internal organ, it has no somatic nerve supply, and biliary colic due to infection and inflammation of the biliary tract is not a somatic pain. Rather, pain may be caused by luminal distension, which causes stretching of the wall.
The pancreas further produces large amounts of bicarbonate, secreting this through the pancreatic duct to the duodenum to neutralize gastric acid passing into the digestive tract. The secretion is a complex and relatively energetically expensive process.