digestive system prevod, englesko - srpski rečnik

Prevod reči: digestive system

Smer prevoda: engleski > srpski

digestive system [ imenica ]
Generiši izgovor

The system that makes food absorbable into the body; SYN. gastrointestinal system.
Mouth, stomach, intestine, and associated glands of animals, which are responsible for digesting food. The food is broken down by physical and chemical means in the stomach; digestion is completed, and most nutrients are absorbed in the small intestine; what remains is stored and concentrated into feces in the large intestine. In birds, additional digestive organs are the crop and gizzard.
In smaller, simpler animals such as jellyfishes, the digestive system is simply a cavity (coelenteron or enteric cavity) with a “mouth” into which food is taken; the digestible portion is dissolved and absorbed in this cavity, and the remains are ejected back through the mouth.
mouth, pharynx, and esophagus
In humans digestion takes place in the alimentary canal, which starts at the mouth, continues as the pharynx, esophagus, stomach, intestines, and rectum, and ends at the anus. In the mouth occur mastication and salivation. The purpose of mastication is to crush and grind the food into small particles. The saliva is poured into the mouth from three pairs of glands named parotid, submandibular, and sublingual. The parotid gland secretes a clear saliva, the other two a sticky saliva containing mucin. The saliva moistens the food so that it can be rolled by the tongue and palate into a soft bolus. Saliva also has an important chemical action, for by means of an enzyme called ptyalin cooked starch in the food is converted into maltose, a kind of sugar. When the food is sufficiently masticated, it is pushed backward by the tongue into the pharynx where the swallowing reflex causes a series of muscular movements which propel the food into the gullet or esophagus and thence into the stomach.
The stomach is entered by the cardiac orifice which relaxes to admit the food and then closes. The mucous membrane of the stomach is lined with columnar epithelium, in which are embedded little pits called the gastric glands. From these glands gastric juice pours when they are stimulated by the approach of food. The muscular coat of the stomach produces movements which churn the food and tend to urge it toward the intestine. The pylorus (Greek “gate-keeper”), or orifice leading from the stomach, opens only in response to an acid stimulus; as the food received from the gullet is alkaline owing to the presence of salivary secretions, it remains in the stomach until thorough admixture with the gastric juice has rendered it acid. Gastric juice contains hydrochloric acid and an enzyme called pepsin (which is released as a precursor called pepsinogen), by which the proteins in the food are converted into polypeptides. In babies, an enzyme called rennin, which coagulates milk, is present. The stomach proceeds to dis
charge its contents into the intestine about half-an-hour after the commencement of a meal, though it takes about three hours to empty itself.
small and large intestine
The small intestine secretes a juice called succus entericus or intestinal juice; and two other secretions, pancreatic juice and bile, enter by their ducts, which open into the duodenum, or first part of the small intestine. Pancreatic juice contains three enzymes: trypsin (released as a precursor, trypsinogen) which attacks proteins more completely than gastric juice, converting them into amino acids; amylase, which converts starch into maltose, thus taking over the function of salivary juice whose activity is stopped in the stomach; and lipase, which splits the fats into glycerin and fatty acids. Bile by itself has no digestive action, but it aids the action of lipase. The intestinal juice contains the following enzymes: enterokinase, which is concerned in the production of trypsin; aminopeptidases, which aid trypsin in the breaking up of polypeptides; and enzymes that convert maltose and other sugars into glucose.
Covering the surface of the mucous membrane of the small intestine are a large number of small prominences called villi. These increase the surface for absorption, by which the products of digestion of protein and carbohydrate diffuse into small bloodvessels lying immediately under the epithelium. The glycerin and fatty acid are carried into the central lacteal or lymphatic vessel and are again united into small globules of fat. The amino acids from the proteins are carried in the blood stream to repair and build up the tissues; and excess is converted by the liver into urea, which is sent to the kidneys to be disposed of. The tiny globules of fat pass into the thoracic duct, whence they find their way into the bloodstream and ultimately into the tissues, where they produce heat by oxidation or are stored up in the form of adipose tissue. The sugar is temporarily stored in the liver as glycogen and given out as glucose when required.
The small intestine is about 6.9 m long and the passage of the food occupies about four hours. It then travels more slowly through the 1.2 m of large intestine, taking from to hours to reach the rectum. During this time, water is absorbed and the waste residue is gradually compressed as a compact mass into the rectum and finally is expelled by the anus.

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