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Digestion is the process of physical and chemical processing of food in the gastrointestinal tract to elementary particles nutrients that can absorbed into the blood and lymph through the intestinal wall and participate in the metabolism of the body. Such elementary particles are: for fat - glycerol and fatty acids, protein, amino acids, carbohydrates - monosaccharides.
Digestive activity begins from the moment of receipt of food in the mouth. In this activity are actively involved not only the chewing muscles and salivary glands, but also the entire digestive system. In experiments I. P. Pavlov from "imaginary feeding the dogs, when food is in the stomach not fell, and fell out of the hole cut of the esophagus, it was found that the stomach secretion begins in 6-8 minutes, and pancreas after 3 to 4 minutes after the start of a meal. Received the oral cavity food is machined and moistened with saliva. Released saliva creates conditions for formation of a food lump and promotes digestion make up the food carbohydrates, as in the composition of the saliva of a person are enzymesthat digest carbohydrates, - amylase (ptyalin) and Maltese. Under the influence of the food saliva reflex due to the spread of stimulation of receptors mucous membrane of the tongue to sljunootdelitelnoe center located in the medulla, and thence by the fibers of the parasympathetic and sympathetic nerve to the salivary glands. Impact on sljunootdelitelnoe center can provide not only food, but also an idea about it, and kind of food, smell, i.e. salivation happens on the conditioned-reflex type.
Depending on the composition and texture of the food product to the changing nature of the emitted saliva. When more than a dry food saliva more and more liquid. The secretion of such saliva is provided by the effect of parasympathetic nerve. Under the influence of the sympathetic nerve, on the contrary, stands out thick saliva and in small numbers. If the secretion of liquid saliva has a special filtration of water from the bloodstream into the duct, the allocation of thick saliva is a result of intensification of metabolic processes of the gland and the secretion of the formed organic substances. Therefore, the sympathetic innervation has on salivary gland not only secretory, but trophic influence.
Great value for changes in the composition of saliva also has a different impact both innervation on blood cancer. Chewed food in the form of a lump served at the root of the tongue. In the result of swallowing movements associated with the rise of the larynx and closing her epiglottis, as well as by the reduction of muscles of the pharynx, the lump is translated from the mouth to the esophagus. In the peristaltic waves of the walls of the esophagus food ball enters the stomach.
Peristaltic wave occurs as a result of processes of excitation and braking circular and longitudinal muscles. The process of excitation and reduce groups of circular and longitudinal fibers of the muscles of the esophagus higher food lump coincides with braking and relaxation groups muscle fibers below it. The result is a food lump as if pressed from the esophagus to the stomach. Food is delayed in the mouth for a very short time, so the digestion of carbohydrates under the influence of enzymes saliva occurs in the stomach and lasts as long as the food supply does not become acidic gastric juice. The acidity of gastric juice depends on the presence of hydrochloric acid, the content of which it around 0.5%. In the stomach, addition of hydrochloric acid, which is excreted obkladochnykh cells, primary cells glands is secreted enzyme pepsinthat digest proteins to albums and peptone. Gastric secretion is not only under the influence of the nervous mechanism, but humoral influences - through blood by chemical transmitters. The influence of the nervous system extends from receptors mucous membranes of the oral cavity to the glands of the fundus and the body of the stomach by wandering nerve. On the same nerve is also affected muscles apparatus of the stomach. Nervous effect on the secretion of the stomach is connected with the very act of eating, and therefore this part secretion was named secretion of the first phase. By ingestion of food in the stomach begins the second phase, associated with irritation of the mucous membrane of the stomach and especially in the pyloric portion. Is this secretion under the influence of humoral substances as included in the composition of the food or food digestion and specific hormone gastrin, which is formed in the mucosa of the pyloric portion of the stomach. By the end of digestion of the stomach secretion gradually decreases, which occurs under the influence of two other hormones: gastrulation and interogation. First formed in the mucosa of the pyloric portion of the stomach, the second - in the mucosa of the upper section of the small intestine. Interrogation is formed under the influence of fat, its products of digestion and hydrochloric acid.