The New Student's Reference Work/Stomach

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Stom′ach, an organ of digestion, present in some form in all animals above the sponges, with the exception of a few degenerated parasites. It is merely a receptacle for the food, and is provided with glands which secrete a digestive fluid. Digestion however, is carried farther and completed in the intestine and, therefore, the stomach is not the sole organ of digestion. The stomach of the human body is a sac on the left side just below the diaphragm. It has four coats: an outer, firm, serous coat; a muscular coat, with fibers arranged in longitudinal, transverse and oblique directions; a coat of loosely woven fibrous tissue; and an inner, mucous coat. The glands which secrete the gastric juice are derived from the latter coat. There are two varieties, those nearer the heart, called cardiac glands, and those at the other end of the stomach where the intestine is joined, called the pyloric glands. The latter are the more important. The stomach is under control of the nervous system, both as to its movements and as to the secretion of gastric juice. When food is introduced into the stomach, the secretion of gastric juice is stimulated through the nervous system. The gastric juice contains a ferment called pepsin, which acts especially on proteids like lean meat, white of eggs, gluten of bread etc. This action takes place in the presence of acid, and in the glands are certain cells which provide hydrochloric acid in small amount. When this is deficient, grave stomach disorders arise. The food is reduced to a condition called chyme and is passed on into the intestine. The object of digestion is to render food soluble that it may pass by absorption through the walls of the stomach and intestine. This is not a process depending upon life, as it can be performed with artificial gastric juice outside the body. The characteristic action of the gastric juice is upon proteids, while the pancreatic juice, which is introduced into the intestine, is a universal digester, of greater efficiency than the gastric juice. It aids in the digestion of starches and fats as well as in completing that of the proteids.