Human saliva

Human saliva is a secretion that is secreted by the salivary glands (large and small). The total volume of saliva produced during the day ranges from 1,000 to 1,500 ml (pH 6.2-7.6). At rest, saliva usually has an acidic reaction, while functioning - alkaline. The viscosity of saliva largely depends on the type of stimulator and the rate of saliva secretion.

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Composition of saliva

Saliva contains the enzyme alpha-amylase, protein, salts, ptyalin, various inorganic substances; Cl anions, Ca, Na, K cations. A relationship has been established between their content in saliva and blood serum. Small amounts of thiocyanin, which is an enzyme and activates ptyalin in the absence of NaCl, are found in the secretion of saliva. Saliva has an important ability to clean the oral cavity and thereby improve its hygiene. However, a more important and significant factor is the ability of saliva to regulate and maintain water balance. The structure of the salivary glands is arranged in such a way that they usually stop secreting saliva as the amount of fluid in the body decreases. In this case, thirst and dryness in the mouth appear.

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Saliva secretion

The parotid salivary gland produces a secretion in the form of serous fluid and does not produce mucus. The submandibular salivary gland and, to a greater extent, the sublingual gland, in addition to serous fluid, also produce mucus. The osmotic pressure of the secretion is usually low, it increases as the speed of secretion increases. The only enzyme, ptyalin, produced in the parotid and submandibular salivary glands, participates in the breakdown of starch (the optimal condition for its breakdown is pH 6.5). Ptyalin is inactivated at pH less than 4.5, as well as at high temperatures.

The secretory activity of the salivary gland depends on many factors and is determined by such concepts as conditioned and unconditioned reflexes, hunger and appetite, a person's mental state, as well as mechanisms that occur during food intake. All functions in the body are interconnected. The act of eating is associated with visual, olfactory, gustatory, emotional and other functions of the body. Food, irritating the nerve endings of the oral mucosa with its physical and chemical agents, causes an unconditioned reflex-impulse, which is transmitted to the cerebral cortex and the hypothalamic region along the nerve pathways, stimulating the masticatory center and salivation. Mucin, zymogen and other enzymes enter the cavities of the alveoli, then - into the salivary ducts, which stimulate the nerve pathways. Parasympathetic innervation promotes the release of mucin and the secretory activity of the channel cells, sympathetic - controls the serous and myoepithelial cells. When eating tasty food, the saliva contains a small amount of mucin and enzymes; when eating sour foods, the saliva contains a high protein content. Unpalatable foods and some substances, such as sugar, lead to the formation of a watery secretion.

The act of chewing occurs due to the nervous regulation of the brain through the pyramidal tract and its other structures. Chewing of food is coordinated by nerve impulses coming from the oral cavity to the motor node. The amount of saliva required for chewing food creates the conditions for normal digestion. Saliva moistens, envelops and dissolves the forming food lump. Decreased salivation up to complete absence of saliva develops in some diseases of the GS, for example, in Mikulicz's disease. Also, excessive salivation causes local irritation of the mucous membrane, stomatitis, gum and dental disease and negatively affects dentures and metal structures in the oral cavity, causing dehydration of the body. Changes in the secretion of the GS lead to disruption of gastric secretion. Synchronicity in the work of paired GS has not been sufficiently studied, although there are indications of its dependence on a number of factors, for example, on the condition of the teeth on different sides of the dentition. At rest, the secret is secreted insignificantly, during irritation - intermittently. During the digestion process, the salivary glands periodically activate their activity, which many researchers associate with the transition of gastric contents into the intestines.

How is saliva secreted?

The mechanism of secretion of the salivary gland is not entirely clear. For example, during denervation of the parotid gland after the introduction of atropine, an intense secretory effect develops, but the quantitative composition of the secret does not change. With age, the chlorine content in saliva decreases, the amount of calcium increases, and the pH of the secret changes.

Numerous experimental and clinical studies show that there is a connection between the salivary glands and the endocrine glands. Experimental studies have shown that the parotid salivary gland enters the process of regulating blood sugar earlier than the pancreas. Removal of the parotid salivary glands in adult dogs leads to insular insufficiency, the development of glycosuria, since the secretion of the salivary glands contains substances that delay the release of sugar. The salivary glands affect the preservation of subcutaneous fat. Removal of the parotid salivary glands in rats causes a sharp drop in the calcium content in their tubular bones.

The connection between the activity of the genital tract and sex hormones has been noted. There are cases where the congenital absence of both genital tracts was combined with signs of sexual underdevelopment. The difference in the frequency of genital tract tumors in age groups indicates the influence of hormones. In tumor cells, both in the nuclei and in the cytoplasm, receptors for estrogen and progesterone are found. All the listed data on the physiology and pathophysiology of the genital tract are linked by many authors with the endocrine function of the latter, although no convincing evidence is provided. Only a few researchers believe that the endocrine function of the genital tract is beyond doubt.

Often, after an injury or resection of the parotid gland, a condition called parotid hyperhidrosis or auriculotemporal syndrome develops. A unique symptom complex develops when, during a meal, due to irritation by a taste agent, the skin of the parotid-masticatory region turns sharply red and severe local sweating appears. The pathogenesis of this condition is completely unclear. It is assumed that it is based on an axon reflex carried out by the taste fibers of the glossopharyngeal nerve, passing through anastomoses as part of the auriculotemporal or facial nerves. Some researchers associate the development of this syndrome with trauma to the auriculotemporal nerve.

Observations on animals have shown the presence of regenerative abilities of the parotid gland after organ resection, the severity of which depends on many factors. Thus, guinea pigs have a high regenerative ability of the parotid gland with significant restoration of function after resection. In cats and dogs, this ability is significantly reduced, and with repeated resection, the functional ability is restored very slowly or not restored at all. It is assumed that after removal of the opposite parotid gland, the functional load increases, the regeneration of the resected gland accelerates and becomes more complete.

The glandular tissue of the SG is very sensitive to penetrating radiation. Irradiation in small doses causes temporary suppression of the gland function. Functional and morphological changes in the glandular tissue of the SG were observed in the experiment with irradiation of other areas of the body or general irradiation.

Practical observations show that any of the SGs can be removed without harm to the patient's life.