Salivary gland structure

The structure of the human salivary glands is divided into alveolar, tubular and alveolar-tubular. They represent a well-developed system of ducts that connect into a large excretory duct. Minor salivary glands are similar to large ones, but are less complex: they have a secretory part and a short excretory duct.

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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 stroma - thin fibrous connective tissue. The stroma is of mesenchymal origin and, as in the mammary and sweat glands, plays a major role in regeneration, involution and the development of neoplastic processes in the salivary gland. Serous, mucous and serous-mucous secretion of the salivary gland is saliva - a product of the eccrine, less often merocrine, in some segments, apocrine sections of the excretory duct. The secretory or terminal section in the parotid SG is serous, mixed with a predominance of serous acini - in the submandibular salivary gland and mixed with a predominance of mucous acini - in the sublingual salivary gland. Secretory cells of the terminal part of the parotid salivary gland consist of epithelial pyramidal cells with a conical end directly emerging from the acinus. They contain cytoplasmic secretory granules, secrete albumin. "Serous" or "proteinaceous" - shows the reaction to mucus; they contain serous enzymatic particles (cells containing granules of proenzyme, devoid of digestive enzymes), the same as the existing special serous enzymatic cells. The presence of mucus in the secretory cells is shown by a positive reaction with mucincarmine, thionine and alcian blue. Transformation of serous cells into mucus-producing ones is rare, and not only in the parotid SF, but also in other serous SF.

Inflammation of the parotid salivary 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 interepithelial secretory cells and the basement membrane. They are stellate, sometimes spindle-shaped, with a flattened apex, a vesicular nucleus, and delicate acidophilic cytoplasm. The cytoplasm contains coarse, dark-colored fibrils that wrap around the secretory cells like a "basket." The contractile fibrils contain actomyosin (a protein found in flat muscle cells). Under an electron microscope, the cytoplasm of myoepithelial cells is similar to that found in flat muscle cells. There is a similarity in the content of myofibrils, organelles, and some differentiation of the cell membranes. However, flat muscle cells are located on the basement membrane, but only with their surface toward the connective tissue. Desmosomes contain myoepithelial and secretory cells. Functionally, myoepithelial cells behave like flat muscle cells. Due to their ability to contract, they facilitate the movement of secretion into the excretory duct. Myoepithepial 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. The terminal segment, dense neck, isthmus and interlobular duct open directly into the secretory part of the salivary gland. The interlobular duct is long and narrow, and may branch over time. It has a single layer of cuboidal cells with slightly acidophilic, scanty cytoplasm, contains a number of mitochondria and vacuoles concentrated around the nucleus. The cell nucleus is round, rich in chromatin, which gives an intense stain with hematoxylin. The epithelium of the interlobular ducts shows the ability to undergo 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 transform into mucous, serous or squamous cells and oncocytes.

The tubules of the intra- and interlobar ducts are lined with tall cylindrical cells lying on the basal membrane. Their small round nucleus is located in the upper part of the cell. Acidophilic cytoplasmic granules are arranged in parallel rows in the lower part of the cell. Under the electron microscope, parallel rows of mitochondria are visible between the folds of the cell membrane. This structure of the salivary glands significantly increases the cellular surface and is important for the transport of water and calcium salts into the cellular secretion. The apical part contains a number of vacuoles. The cells of the salivary gland tubules are similar to the proximal convoluted tubules of the kidney and have some capacity for water reabsorption. The energy required for this function is provided by a large number of mitochondria, which carry out and coordinate enzymatic oxidation.

The large excretory salivary duct has a wide lumen and is lined with columnar cells with basophilic cytoplasm. Their nuclei are located in the lower part of the cell near the basement membrane. Mucus-secreting goblet cells are occasionally found in the epithelium. Their number increases significantly in pathological conditions. Rarely encountered, single myoepithelial cells are located between the epithelial cells and the basement membrane. The terminal segment of the excretory duct is lined with flat columnar cells and pre-existing squamous epithelium adjacent to the mucous membrane.

The structure of the parotid and submandibular salivary glands is complex. They are alveolar glands, the sublingual is a complex mixed (alveolar-tubular) gland.