Digestion is one of the processes by which food is incorporated in the living body. In digestion, the food is softened and converted into a form which is soluble in the watery fluids of the body, or, in case of fat into very minute globules.
Salivary digestion begins as soon as the food enters the mouth. The object of chewing is not only to bruise the food and make it more permeable for gastric juice, but also to mix starchy parts thoroughly with saliva. This process goes on after swallowing, for the first twenty minutes or half-hour that the food remains in the stomach, after which the action of the saliva is checked by the acid of the gastric juice.
Gastric digestion begins a little time after the food enters the stomach. The gastric juice begins to be secreted even before the food enters the stomach, at the sight and smell of food. This juice contains two ferments named pepsin and rennin. There are also present free hydrochloric acid and acid salts. The main function of the stomach is to render the ingested food soluble, and mix it thoroughly with the gastric juice until it assumes a gruel-like consistency. This material, known as chyme, is then passed through the pylorus into the intestine. Gastric digestion requires from about an hour to six or seven hours depending on the food eaten.
Intestinal digestion. The softened food or chyme which leaves the stomach is exposed to the action of four factors – bile, pancreatic juice, intestinal juice, bacteria. The bile consists mainly of certain complex salts and pigments, which assist in digesting the fats of the food, and partly consists of waste products removed from the blood. The pancreatic juice contains four powerful ferments – lipase, chymotrypain, amilase and trypsin. Intestinal juice also contains ferments (enzymes). Bacteria are normal inhabitants of both small and large intestines. In the former they have a fermentative, in the latter – a putrefactive action. The intestinal bacteria also play an important and valuable role in the manufacture of certain components of the vitamin B complex.
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Date: 2015-04-20; view: 1416