Salivary Glands

SALIVARY GLANDS. The oral cavity is the first stage in the digestive tract where food is processed. Crushed by the teeth, it is mixed here with the help of the tongue with saliva and acquires the property of an easily swallowed food bolus. Saliva flows into the oral cavity through numerous ducts of the S. g., partly embedded in the mucous membrane itself (small glands), but mainly of large glands, removed from the mucous membrane by a considerable distance and therefore equipped with large and significant in length ducts. In humans, there are three large glands that secrete saliva: the parotid gland (gl. parotis) (see Parotid gland), the submandibular (gl. submaxillaris) (see Submandibular gland), and the sublingual (gl. sublingualis) (see Sublingual gland). In the dog, the orbital gland (gl. orbitalis) should also be included among them. For a detailed description of them, see the respective articles. Small glands, ranging in size from a millet grain to a lentil, are scattered throughout the mucous membrane of the entire oral cavity. Their excretory ducts are no more than 0.5 mm in length and open in various places of the mucous membrane. Depending on their location, the following groups are distinguished: labial S. g. (gl. labiales), located between the mucous membrane and m. sphincter oris; buccal glands (gl. buccales); lingual glands (gl. linguales) - a series of small glands extending from the tip to the base of the tongue along its edge. At the tip of the tongue, in the depth of its muscular layer, there is a significant group of small glands called Nuhn's gland (gl. Nuhnii). A special group of lingual S. g. are the glands of papillae foliatae and papillae vallatae, located under the mucous membrane in the area of the foliate papillae and the papillae surrounded by a ridge. Their excretory ducts open in the depth of the grooves pp. circumvallatae and deep grooves pp. foliatae. Behind these glands, up to the epiglottis, under the layer of mucous membrane, there is a continuous layer of S. g. of the base of the tongue with small excretory ducts. Finally, there are palatine glands (gl. palatinae) - a fairly significant layer of glands extending from the middle of the hard (palate) to the beginning of the soft palate. All the S. g. listed above are built on the same type - tubulo-alveolar glands and consist of excretory ducts, secretory tubules, intercalated parts, and lobules (acini). Their excretory ducts are lined with a completely atypical for glandular tissue stratified squamous epithelium; the secretory tubules, as branches of the ducts, have a rod-shaped epithelium, in which the part facing the wall of the tube shows a distinct striation, while the part adjacent to the lumen appears homogeneous. The intercalated parts have a spindle-shaped epithelium, which deeply penetrates into the lobules themselves, as is the case in the parotid gland, or cuboidal, transitioning without sharp boundaries into the glandular epithelium of the lobules themselves. The latter, depending on the nature of the secreted secretion, has specific characteristics that distinguish this gland from others. Depending on the nature of the glandular epithelium and its associated function, S. g. are divided into the following groups: 1) Serous, or proteinaceous, producing a watery secretion containing protein and mineral salts. These include: the parotid gland, the glands of pp. vallatae and foliatae of the tongue. In the secretion of gl. parotis, mucin can sometimes be found, the origin of which is associated with the secretion of small mucous glands embedded in the thickness of the gland itself or located along the course of Stensen's duct, into which their secretion is poured. 2) Mucous, secreting a mucous, thread-drawing liquid containing mucin, salts and a small amount of protein. These include: among the large ones, the sublingual, and among the small ones - the glands of the tongue, lips, pharynx, and part of the glands of the soft palate. 3) Mixed glands, which in their composition have both mucous and serous cells. This type also includes glands containing in various proportions purely mucous cells and special cell clusters known as Gianuzzi's half-moons (Gianuzzi). These clusters of protein-rich cells adjoin directly to the membrana propria of the gland, while ordinary mucous cells face its lumen. Together with a large amount of mucin, Gianuzzi's half-moons secrete a significant amount of protein (A. Ebner). The representative of this group among the S. g. is the sublingual gland (gl. sublingualis). The histological picture of the glands varies depending on whether we are dealing with a gland in a resting or active state, to which Heidenhain (K. Heidenhain) first drew attention. The cells of mucous glands in a resting state are large, have a light transparent protoplasm and a nucleus attached to the wall of the cell. In an active gland, the cells are reduced in volume, their protoplasm is less transparent and filled with small granules; in form and structure they very much resemble the half-moons of Gianuzzi described above. The nuclei of the cells are located more centrally. The protoplasm of the cells of serous glands is also transparent in a resting state, in which a small-granular mass is embedded in a small amount; the nucleus is slightly notched. In an active state, the cells are also reduced in volume, the protoplasm appears as a solid small-granular mass, the nucleus is of a regular, round shape. The relationship of nerve elements to the glands, according to Krause and Retzius (Krause, Retzius), is as follows: nerve bundles entering the hilus of the gland consist predominantly of myelinated fibers. The latter form a plexus around the excretory ducts, which includes ganglion cells. From this plexus, in turn, myelinated fibers depart, which form a dense nerve plexus adjoining the membr. propria of the gland and, with their branches, enveloping the glandular cells.

D. Romashov