The structure of the salivary glands
Last reviewed: 23.04.2024
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The structure of human salivary glands lies in dividing them into alveolar, tubular and alveolar-tubular. They represent a well-developed system of ducts that connect to a large excretory duct. Small salivary glands are similar to large, but are less complicated: they have a secretory part and a short excretory duct.
[Internal structure of the salivary glands
The parenchyma of the salivary gland consists of primary lobules that form the lobes of the gland and are separated by a stroma - a thin fibrous connective tissue. The stroma has a mesenchymal origin and, as in the dairy and sweat glands, plays a crucial role in the regeneration, involution and development of neoplastic processes in the salivary gland. The serous, mucous and serous-mucous secretions of the salivary gland are saliva, a product of the externic, less often mekrinin, in some segments, apocrine regions of the excretory duct. The secretory or terminal part of the parotid gland is serous, mixed with the prevalence of serous acini - in the submandibular salivary gland and mixed with the predominance of mucous acini - in the sublingual salivary gland. The secretory cells of the terminal portion of the parotid salivary gland consist of epithelial pyramidal with a conical end that directly extends from the acinus. They contain cytoplasmic secretory granules, secrete albumin. "Serous" or "protein" - shows a reaction to mucus; they contain serozoenzymatic particles (cells containing proferment granules lacking digestive enzymes), the same as existing special serous enzyme cells. The presence of mucus in the secreting cells shows a positive reaction with mucin carmine, thionin and Alcian blue. The transformation of serous cells into producing mucus is rare, and not only in the parotid gland, but in other serous SJ.
Inflammation of the parotid gland (in the secretory and excretory parts) leads to mucous metaplasia of individual cells, causing changes in the epithelial cells of a significant part of the duct.
Myoepithelial cells lie between the epithelial secretory cells and the basal membrane. They have a stellate shape, sometimes spindle-shaped with a flattened apex, a bubble nucleus and a gentle acidophilic cytoplasm. The cytoplasm contains coarse, dark fibrils that wrap around the secretory cells like a "basket". Compressing fibrils contain actomyosin (a protein found in flat muscle cells). Under the electron microscope, the cytoplasm of myoepithelial cells is similar to that found in plane muscle cells. There is a similarity in the content of myofibrils, organelles and some differentiation of cell membranes. However, flat muscle cells are located on the basement membrane, but only the surface to the connective tissue. Desmosomes contain myoepitepial and secretory cells. Functionally, myoepithelial cells behave like flat muscle cells. Due to the ability to reduce, they promote the advance of secretion into the excretory duct. Myoepitepial cells play an important role in the pathogenesis of many salivary gland tumors.
The excretory ducts of the salivary gland are well separated; The structure of individual segments differs anatomically and functionally. End segment, dense neck, isthmus and interlobular duct open directly into the secretory part of the salivary gland. Interlobular duct - long and narrow, with time can branch. It has a single layer of cuboidal cells with a slightly acidophilic, lean cytoplasm, contains a number of mitochondria and vacuoles concentrated around the nucleus. The cell nucleus is round, rich in chromatin, which gives an intense coloration with hematoxylin. The epithelium of interlobular ducts shows the ability to multidirectional modifications. The structure of this segment of the duct is considered a "proliferation zone". In pathology, inflammatory or neoplastic, the cells of the interlobular duct proliferate and can be transformed into mucous, serous or scaly cells and oncocytes.
The tubules of the intra- and interlobular ducts are lined with high cylindrical cells lying on the basal membrane. Their small round nucleus is located in the upper part of the cell. The acidophilic cytoplasmic granules are arranged in parallel rows in the lower part of the cell. Under the electron microscope, parallel rows of mitochondria between the folds of the cell membrane are visible. This structure of the salivary glands significantly increases the cell surface and is important for transporting water and calcium salts into the cellular secret. The apical part contains a number of vacuoles. Cells of the tubules of the salivary gland have a similarity to the proximal convoluted tubules of the kidney and have some ability to reabsorb water. The energy required for this function is provided by a large number of mitochondria, which carry out and coordinate the enzymatic oxidation.
The large excretory salivary duct has a wide lumen and is lined with cylindrical cells with a basophilic cytoplasm. Their nuclei are localized in the lower part of the cell next to the basal membrane. Mucus-secreting goblet cells from time to time occur in the epithelium. Their number increases significantly with pathological conditions. Rarely occurring, single myoepithelial cells are located between epithelial cells and the basal membrane. The terminal segment of the excretory duct is lined with flat cylindrical cells and the already existing squamous epithelium adjacent to the mucous membrane.
The structure of the parotid and submandibular salivary glands is complex. They are alveolar glands, sublingual - a complex mixed (alveolar-tubular) gland.