Intestine, the portion of the digestive apparatus situated below the stomach, divided into the small and large intestines. The former includes the duodenum, jejunum, and ileum; the latter the caecum, colon, and rectum. Many of the details on these organs have been given in the articles Alimentary Canal, Caecum, Colon, and Comparative Anatomy, and need not be here repeated. Next below the stomach comes the duodenum, the largest portion of the small intestine, about 12 in. long, receiving the ducts from the liver and pancreas, and furnished with numerous circular internal folds of mucous membrane (the valvulae conniventes); above it is in contact with the liver and gall bladder, in front with the stomach and arch of the colon, and behind with the spinal column, right kidney, vena cava, aorta, and diaphragm; its arteries come chiefly from the superior mesenteric, and its nerves from the solar plexus. The jejunum and ileum, which follow, have no distinct line of separation, and may be described together as a canal four or five times as long as the body, arranged in numerous folds or convolutions, freely movable in front and on the sides, and attached to the mesentery behind; the upper portion is called jejunum from its being generally found empty.
In front these are in relation with the omentum and the anterior abdominal wall, behind with the spine, and in various places with the large intestine; internally the structure resembles that of the duodenum, the valvuhe diminishing gradually from above downward; the mucous membrane is studded with glandular follicles, and contains also the patches of Peyer, the seat of lesion in typhoid fever. Of the large intestine the only portion to be alluded to is the rectum, the terminal portion, ending in the anal opening protected by sphincter muscles; it lies in the concavity of the sacrum, is cylindrical, mostly on the median line, and somewhat dilated at the lower end; its principal relations in both sexes are with the genitourinary organs. Internally it presents longitudinal and parallel folds, with transverse semilunar wrinkles forming sacs in which fa3cal matter is often lodged for a long time; its mucous membrane possesses considerable absorbent powers, and may be used for introducing nutriment and medicine. - The common peristaltic movements of the intestinal canal depend upon the contractility of the muscular coat called into action by the stimulus of the contents, and are not dependent upon cerebrospinal nervous influence, though they may be modified through the spinal and sympathetic systems.
In the duodenum and beginning of the jejunum are small branching clusters of follicles, the glands of Brunner. The follicles of Lieberkuhn are simple open glandulae, straight narrow caeca, very abundantly distributed through the entire length of the intestinal tube. The product of these two sets of glandular follicles is the intestinal juice, a colorless, viscid, alkaline secretion, which rapidly converts hydrated starch into sugar, and probably also effects other important changes in the digestive process. When the extent of these glandular structures of the intestine is considered, the beneficial action of purgative medicines, in hastening the removal of various morbific matters from the system by direct stimulation, may be easily understood.