alimentary canal


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digestive system

digestive system, in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex. It consists of the gastrointestinal tract (gut), an extensive tube extending from the mouth to the anus, through which the swallowing, digestion, and assimilation of food and the elimination of waste products are accomplished.

The Human Digestive System

In the digestive system, ingested food is converted into a form that can be absorbed into the circulatory system for distribution to and utilization by the various tissues of the body. This is accomplished both physically, by mastication in the mouth and churning of the stomach, and chemically, by secretions and enzymes of the gastrointestinal tract. Beginning at the mouth, all food passes through the alimentary canal (pharynx, esophagus, stomach, and intestines) before it reaches the anus, where undigested matter is eliminated as waste. The outer walls of the digestive tract are composed of layers of muscle and tissue that undergo waves of contraction (peristalsis), thereby pushing the food along its digestive path. The inner lining contains glands that secrete the acids and enzymes necessary to break down food into a form utilizable by the body.

Digestion begins in the mouth, where chewing reduces the food to fine texture, and saliva moistens it and begins the conversion of starch into simple sugars by means of an enzyme, salivary amylase. The food is then swallowed, passing through the pharynx and down the muscular esophagus, or gullet, to the expanded muscular pouchlike section of the gastrointestinal tract, the stomach. Specialized cells in the stomach secrete digestive enzymes and gastric juices, which act on the partially digested food. The stomach also physically churns and mixes the food. The stomach secretions include the enzyme pepsin, which acts on proteins; hydrochloric acid, essential for the action of pepsin; and an enzyme, gastric lipase, which begins the breakdown of fats. The gastric juices of young children contain, in addition to those just mentioned, the enzyme rennin, which acts on milk. Some foods, including simple sugars and alcohol, are absorbed directly through the stomach wall and do not remain in the stomach. Most food, however, is not absorbed in the stomach and passes into the duodenum (first section of the small intestine) in the form of a thick liquid called chyme.

Digestive enzymes from the pancreas and bile from the liver act on the chyme in the duodenum. These enzymes include pancreatic lipase, which breaks down fats into glycerol and fatty acids; pancreatic amylase, which continues the breakdown of starches and most other carbohydrates into disaccharides; and trypsin and erepsin, which break down whole and partially digested proteins (proteoses and peptones) into amino acids, the end products of protein digestion. Bile is essential for emulsifying large fat globules into smaller ones that are more easily digested by pancreatic lipase. In addition, intestinal juices are secreted by small glands in the intestinal wall called the crypts of Lieberkühn. Like the pancreatic juices, intestinal juices contain enzymes that continue the digestion of proteins and fats and also contain three enzymes that break down disaccharides into glucose, galactose, and fructose (simple sugars). The digested food is absorbed into the circulatory and lymphatic systems through small fingerlike projections of the intestinal wall, called villi. Undigested material passes into the large intestine, where most of the water is absorbed and the solid material, or feces, is excreted through the anus.

Bibliography

See J. E. Morton, Guts: The Form and Function of the Digestive System (1967); H. W. Davenport, Physiology of the Digestive Tract: An Introductory Text (3d ed. 1971).

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alimentary canal

[¦al·ə¦men·trē kə′nal]
(anatomy)
The tube through which food passes; in humans, includes the mouth, pharynx, esophagus, stomach, and intestine.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

alimentary canal

, tract
the tubular passage extending from the mouth to the anus, through which food is passed and digested
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Table 1: Antimicrobial activity of alimentary canal extracts from the red palm weevil larvae against different microbial species.
nigra Color of living animals Black and shiny Tunic Smooth Oral siphon Bent dorsally, 8-10 lobes, usually not visible in living animals Atrial sphon Anterior to the middle of the body Right side Longitudinal transverse, and oblique fibers; longitudinal musculature wider and running toward both the endostyle and the posterior region Peripharyngel groove Both laminas smooth Pharyngeal papillae Absence of intermediate papillae Alimentary canal Occupies more than 2/3 of the left side; intestinal loop at the level of the base of the atrial siphon P.
Fine structure of the alimentary canal of the larval blow fly Chrysomya megacephala (Diptera: Calliphoridae).
Comparative anatomical and histological study of the alimentary canal of Dendroctonus parallelocollis, D.
'Aberrant luminal recanalization' has been discussed as a possible cause in which a portion of alimentary canal may get solidified followed by recanalization4.
Habershon, physician at Guy's Hospital, who wrote in his textbook 'Pathological and Practical Observations on Diseases of the Alimentary Canal'; 'Pouches of the colon sometimes become of considerable size the orifices of these small sacs are bounded by hypertrophied longitudinal and circular fibres and their contents remain almost shut off.
The greatest variety of these genes can be found in the alimentary canal and the mouth; the least diverse variety can be found in the vagina.
The lemon also functions as a preventive medication for many types of conditions and disorders; these include infections of the stomach and the alimentary canal, all kinds of circulatory problems, as well as problems like arteriosclerosis, which is the thickening of the arterial walls in the body leading to symptomatic diseases.
That said, the ins and outs of a child's alimentary canal don't make for breathtaking cinematic excitement, even with breaks for grocery story runs,.
The list includes glucocorticoids and related immunosuppressants, antidiabetic drugs, lithium, Depo-Provera and other contraceptives, cyclooxygenase inhibitors, proton pump inhibitors (pharmaceutical antacids), total parenteral nutrition (this means not administered via the alimentary canal), aromatase inhibitors (letrozole, exemestane, anastrozole), gonadotropin-releasing hormone agonists (Lupron, Lupron Depot, LH-RH agonists, leuprolide), immunosuppressants, anticonvulsants (phenobarbital, phenytoin), cytotoxic drugs, and selective serotonin reuptake inhibitors (SSRIs), which lead to the issue of stress and depression.
While not as photogenic, the utilitarian act of eating, including food consumed, and on the other end of the alimentary canal, food depleted, is fraught with danger and remains extremely central.