salivary glands

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salivary glands

(săl`əvâr'ē), in humans, three pairs of glands that secrete the alkaline digestive fluid, saliva, into the mouth. Most animals have salivary glands that resemble those in humans; however, in some animals these glands perform other functions. For example, the salivary glands of many blood-sucking species secrete a substance that prevents blood coagulation. In humans the largest pair of salivary glands is situated just below and in front of each ear (parotid glands), the second pair is below the jaw (submandibular), and the third is under the tongue (sublingual). Ducts carry the secretions of the salivary glands into the mouth cavity. Together with the mucus secreted by the membrane of the mouth and the secretions of other small glands in the mouth, saliva helps to keep the mouth moist, softens the food as it is chewed, and by means of salivary amylaseamylase
, enzyme having physiological, commercial, and historical significance, also called diastase. It is found in both plants and animals. Amylase was purified (1835) from malt by Anselme Payen and Jean Persoz.
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—the digestive enzyme contained in saliva—converts starch to sugar, thus initiating the process of digestion (see digestive systemdigestive system,
in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex.
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). The flow of saliva is stimulated by the presence of food in the mouth, or even the sight and smell of food. A lack of salivary flow from a gland may be caused by the formation of a calculus, or mineral concretion, that blocks a duct. The parotid glands are subject to growths, usually benign, and to infection (see mumpsmumps
(epidemic parotitis), acute contagious viral disease, manifesting itself chiefly in pain and swelling of the salivary glands, especially those at the angle of the jaw. Other symptoms are fever, a general feeling of illness, and pain on chewing or swallowing.
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).

Salivary Glands

 

glands located in the anterior part of the digestive tract that secrete saliva. They exist in such invertebrates as worms, arthropods, and mollusks, in terrestrial vertebrates, and in man. The salivary glands are involved mainly with digestion, but owing to phylogenetic specialization, the saliva of certain animals serves other purposes as well.

The salivary glands are complex branched tubular or alveolar glands. The larger glands are complex alveolar or tubuloal-veolar glands consisting of secretory portions and a system of ducts through which the saliva reaches the mouth. Each gland is covered with a connective-tissue capsule that divides the organ into lobes. The base of the lobes comprises branches of small efferent ducts that terminate in the secretory portions. These portions, which secrete protein, mucin, and other substances, determine the composition of the saliva. The salivary ducts contain intralobular and interlobular efferent ducts and a common efferent duct. The ductal cells form the walls of the efferent channels and regulate the saliva’s water content and mineral composition.

The salivary glands of worms are unicellular. All mollusks, except bivalves, have one or two pairs of multicellular glands. In insects, the salivary glands are saccular or racemose; the maxillary, mandibular, and labial glands are the salivary glands proper. The labial glands of caterpillars become silk-excreting glands. The level of development of the salivary glands varies among birds; some birds, such as those of the order Pelecani-formes, lack the glands entirely.

In mammals. Terrestrial mammals have numerous small salivary glands situated in the mucous membranes of the tongue, lips, cheeks, and hard and soft palates. In addition, such mammals have three pairs of larger glands—the parotid, sublingual, and submaxillary glands—which are situated some distance from the mouth and are connected with it by ducts. All the salivary glands develop during embryogenesis as outgrowths of the buccal epithelium into the subjacent mesenchyme. The parotid gland is formed during the fourth week of the embryo’s life, the submaxillary in the sixth week, and the sublingual in the eighth or ninth week. The small salivary glands are discernible in the mucous membrane much later.

The parotid gland and some lingual glands are proteina-ceous; they release an enzyme-rich liquid secretion. Other small salivary glands secrete a thicker and more viscid saliva containing glycoproteins. The submaxillary and sublingual glands as well as the salivary glands of the lips, cheeks, and tip of the tongue release a mixed protein and mucin secretion. The composition of saliva depends on the type of food consumed. Mer-ocrine secretion, or secretion occurring without the destruction of the glandular cells, is typical of all the salivary glands.

IA. L. KARAGANOV

In man. The typical complex alveolar salivary glands in man have many secretory portions and a system of ducts that are connected to a common duct opening into the oral cavity. The largest glands, the parotids, are situated in front of the external acoustic meatus. The parotid duct terminates in the buccal mucosa of the vestibulum oris. The submaxillary glands are situated under the margin of the lower jaw; their ducts terminate at the sides of the lingual frenulum. The sublingual glands are in the oral cavity directly under the tongue and their ducts are connected to the ducts of the submaxillary glands.

The saliva is the first agent in the digestive process. The parotid glands secrete saliva rich in proteins and enzymes that help break down starch. Mucinous substances predominate in the saliva produced by the other salivary glands. Diseases of the salivary glands include parotitis, mumps, and sialolithiasis.

REFERENCES

Patten, B. M. Embriologiia cheloveka. Moscow, 1959. (Translated from English.)
Falin, L. 1. Gistologiia i embriologiiapolosti rta i zubov. Moscow, 1963.