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ALIMENTARY CANAL
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ALIMENTARY See also:CANAL , in See also:anatomy. The alimentary canal, strictly speaking, is the whole See also:digestive See also:tract from the mouth to the anus. From the one orifice to the other the See also:tube is some 25 to 3o ft. See also:long, and the See also:food, in its passage, passes through the following parts one after the other:—mouth, pharynx, See also:oesophagus, See also:stomach, small intestines, caecum, large intestines, rectum and anus. Into this tube at various points the salivary glands, See also:liver and See also:pancreas pour their secretions by See also:special ducts. As the mouth (q.v.) and pharynx (q.v.) are separately described, the detailed description will here begin with the oesophagus or gullet. The oesophagus (Gr. oivm, I will carry, and (ID ayeEv, to eat), a See also:muscular tube lined with mucous membrane, stretches from the See also:lower limit of the pharynx, at the level of the cricoid See also:cartilage, to the cardiac orifice of the stomach. It is about 10 in. long (25 cm.) and See also:half to one See also:inch in See also:diameter. At first it lies in the lower See also:part of the See also:neck, then in the See also:thorax, and lastly, for about an inch, in the See also:abdomen. As far as the level of the See also:fourth or fifth thoracic vertebra it lies behind the trachea, but when that tube ends, it is in See also:close contact with the pericardium, and, at the level of the tenth thoracic vertebra, passes through the oesophageal opening of the See also:diaphragm (q.v.), accompanied by the two vagi nerves, the See also:left being in front of it and the right behind. In the abdomen it lies just behind the left See also:lobe of the liver. Both in the upper and lower parts of its course it lies a little to the left of the See also:mid See also:line. Its mucous membrane is thrown into a number of See also:longitudinal pleats to allow stretching. The stomach (Gr. o-TOµaXos) is an irregularly See also:pear-shaped bag, situated in the upper and left part of the abdomen. It is somewhat flattened from before backward and so has an anterior and posterior See also:surface and an upper and lower border. When moderately distended the thick end of the pear or fundus bulges upward and to the left, while the narrow end is constricted to See also:form the pylorus, by means of which the stomach communicates with the small See also:intestine. The cardiac orifice, where the oesophagus enters, is placed about a third of the way along the upper border from the left end of the fundus, and, between it and the pylorus, the upper border is See also:concave and is known as the lesser curvature. From the cardiac to the pyloric orifice, See also:round the lower border, is the greater curvature. The stomach has in front of it the liver (see fig. I), the diaphragm and the anterior abdominal See also:wall, while behind it are the pancreas, left See also:kidney, left See also:adrenal, See also:spleen, See also:colon and mesocolon. These structures form what is known as the stomach chamber. When the stomach is empty it contracts into a tubular See also:organ which is frequently sharply See also:bent, and the transverse colon ascends to occupy the vacant part of the stomach chamber. The last inch of the stomach before reaching the pylorus is Diaphragm See also:Attachment of falciform See also:ligament Right lobe of liver See also:Gall-See also:bladder Transverse colon Small intestine Ascending colon Anterior See also:superior spine Caecum usually tubular and is known as the pyloric canal. Before reaching this there is a bulging known as the pyloric See also:vestibule (see D. J. See also:Cunningham, Tr. R. See also:Soc. of Edinb. vol. xlv. pt. I, No. 2). The pylorus is an See also:oval opening, averaging half an inch in its long See also:axis but capable of considerable distension; it is formed by a special development of the circular muscle layer of the stomach, and during See also:life is probably tightly closed. The mucous membrane of the stomach is thrown into pleats or rugae when the organ is not fully distended, while between these it has a mammillated See also:appearance. Superficial to the mucous coat is a sub-mucous, consisting of loose connective See also:tissue, while superficial to this are three coats of unstriped muscle, the inner oblique, the See also:middle circular and theouter longitudinal. The peritoneal coat is described in the See also:article on the coelom and serous membranes. ' The small intestine is a tube, from 22 to 25 ft. long, beginning at the pylorus and ending at the ileo-caecal See also:valve; it is divided into duodenum, jejunum and ileum. The duodenum is from 9 to 11 in. long and forms a horseshoe or C-shaped See also:curve, encircling the See also:head of the pancreas. It differs from the See also:rest of the gut in being retroperitoneal. Its first part is See also:horizontal and lies behind the fundus of the gall-bladder, passing backward and to the right from the pylorus. The second part runs vertically downward in front of the hilum of the right kidney, and into this part the pancreatic and bile ducts open. The third part runs horizontally to the left in front of the aorta and vena cava, while the fourth part ascends to the left See also:side of the second lumbar vertebra, after which it bends sharply downward and forward to form the duodeno-jejunal flexure. The jejunum forms the upper two-fifths of the rest of the small intestine; it, like the ileum, is thrown into numerous See also:con-volutions and is attached by the mesentery to the posterior abdominal wall. Additional information and CommentsThere are no comments yet for this article.
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