Salivary glands

Salivary glands (glandulae oris) are divided into large salivary glands (parotid, submandibular, sublingual) and small salivary glands (glands of the oral cavity, pharynx, upper respiratory tract). The first - paired, the second - plural.

Among the largest largest is the parotid, the mass of which is 25-30 g. Significantly smaller in size is the submaxillary salivary gland localized in the submandibular triangle of the neck. Even smaller is the sublingual salivary gland, which is located under the mucosa of the anterior part of the bottom of the mouth.

Small salivary glands (glandulae salivariae minores) are located in the thickness of the mucosa and submucosa of the oral cavity. Their value ranges from 1 to 5 mm. The topographic principle distinguishes glandulae labialea, buccales, molar (glandulae molares), palatine (glandulae palatinae) and glandulae linguales (glandulae linguales) glands.

Large salivary glands are outside the walls of the oral cavity, but open into it with the help of excretory ducts.

Regardless of topography and size, all the salivary glands (both small and large) have a general outline of the structure. All salivary glands have ectolormal origin and a complex alveolar or alveolar-tubular structure. Salivary glands have a body (main, secretory department) and an excretory duct. The body is represented by the parenchyma and the stroma of the gland.

Secretory departments (initial parts) in the structure and nature of the secret are divided into protein (serous), mucous (mucous) and mixed (protein-mucous) departments. According to the secretion secretion mechanism, all the salivary glands belong to the glands of the microcrystalline type. Protein glands secrete a liquid secret rich in enzymes. Mucous glands secrete a thicker and more viscous secret containing a large amount of mucin, a substance that contains glycosaminoglycans. 

The inferior ducts of salivary glands are subdivided into intralobular, including intercalary ducts (the initial parts of the protocol apparatus), and the so-called striated ducts.

Symptoms distinguish various diseases of the salivary glands, more here.

The defined ducts of the salivary glands pass into the interlobular ducts, which give rise to a common excretory duct of the gland, which opens with a mouth on the walls of the oral cavity. Insertion ducts are usually lined with cubic and prismatic epitheliocytes, striated by cylindrical epitheliocytes, which are characterized by the presence of invaginations of the basal part of the plasmolemma. Between the invaginations there is a considerable amount of mitochondria, which impart a picture of striation to the cells. Interlobular ducts are lined with a two-layer epithelium, which gradually becomes flat. The total excretory duct of the salivary glands is usually lined with multilayer cuboidal, and in the mouth region - multilayered flat epithelium.  

The inferior ducts of various salivary glands have their own peculiarities. The insertion ducts of the submandibular gland are shorter and less branched than in the parotid gland. In the hyoid gland, intercalary and striated ducts are almost not developed. By type of secretion, the lingual glands are predominantly serous. Mucous glands of the tongue are only in the region of the root of the tongue and along its lateral sides. Mixed lingual glands lie in the anterior part of the tongue. The palatine glands are mucous, and the buccal, molar and labial glands are mixed.

Salivary glands perform exocrine function. It consists in regular discharge into the oral cavity of saliva. Saliva contains water (approximately 99%), mucus (mucin), enzymes (amylase, maltase), inorganic substances, immunoglobulins. Saliva moisturizes the food, moistens the mucous membrane of the mouth. Saliva enzymes cleave polysaccharides to disaccharides and monosaccharides (glucose).

Salivary glands consist of primary lobules (acini), which form the lobe of the gland. They are separated from each other by a well developed connective tissue, in which are located a variety of cellular elements (fat and plasma cells, lymphocytes, etc.), vessels, nerves and ducts. The lobules are represented by several blind sacks, which are terminal, main divisions. The secretory cells of the terminal sections have a cubic or conical shape and are located on a thin basal membrane. Basophilic cytoplasm of these cells contains a large number of secretory granules, the nucleus is located in the lower third of the cell. Close to the basal membrane are also basal (basket) cells, capable of active reduction due to the content of fibrils. These cells belong to the myoepithelial elements. Insertion sections, salivary tubes, excretory ducts, through which saliva successively flows from the terminal section, also contain basal cells lined with cubic or flat epithelium, salivary tubes - prismatic epithelium, excretory ducts - two-row, intercalary sections - highly prismatic epithelium, which, as the terminal The flow passes into a multilayer cubic. The epithelium of intercalary sections and salivary tubes possess secretory activity.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

How does the salivary gland develop?

Salivary glands are present only in vertebrates. The fish and the whale do not. In some reptiles salivary glands are transformed into poisonous glands. Complete evolutionary development of SJ occurs only in mammals.

At the fifth week of fetal embryonic life, the ectodermal epithelium of the oral cavity forms a flat groove that develops into the rudiment of the parotid gland. Later, it takes the form of a tube, the front end of which contacts the epithelium of the oral cavity. The tube is surrounded by a primary mesenchyme, inside which grows the kidney of the salivary rudiment. The parotid gland is gradually divided into the formation of the acini and ducts. In the formed lumen, narrow primary excretory ducts with low cuboidal epithelium are formed. The epithelium is initially single-layer, but in the 7-9-centimeter fetus, the epithelial cells form two layers, and the mucous secret appears in the lumen of the duct. The duct epithelium in some areas ends with alveolar-tubular outgrowths, which later form in the terminal sections. Differentiate goblet cells of interlobular excretory ducts, lining of large ducts. In the 24-week fetus, the terminal sections have two cell layers, the basal layer is represented by myoepithelial cells. Mucous secretion of the primary acini of the duct epithelium decreases as the secretory function of the end sections increases. The mesenchyme, which surrounds the gland, is thin, loose and fibrous. In the late period of embryonic life, the gland is surrounded by a capsule. The budding and freely penetrating mesenchymal substance is surrounded by blood vessels and lymphoid cells, which are collected in similar lymph nodes of the structure. The salivary process grows inside of them, and as a result - a small lymph node containing a salivary substance, is surrounded by the parotid gland. The salivary duct and the acini are found after some time in the mature lymph node. They are observed in deep parotid and in the cervical lymph nodes, located at a considerable distance from the glandular capsule. The heterotopic structure of the salivary glands in the perianthous and extra-lean lymph nodes explains the frequency of adenolymph observed in the parotid region. Salivary tubes and intercalary sections of the salivary glands develop in the postembryonic period of life.

The ovary of the submandibular gland is of an endoderm origin and appears slightly later than that of the parotid gland. Since then, it is located near the rudiment of the diffusely growing parotid gland. After a while, the endoderm of the lower segment of the oral cavity forms the rudiments of the hyoid gland. Despite the fact that the rudiments of the parotid gland appear first, the submaxillary and sublingual glands are organs that have a capsule. Some salivary glands scattered in various parts of the head and neck are heterotopic.

Small salivary glands form much later, and their rudiments appear in the epithelium of the mucous membrane of the oral cavity and pharynx (lips, tongue, hard and soft palate, tonsils, maxillary sinus, larynx, trachea). In the pathological state of the cells of the secretory part of the duct, the SC and epithelium are often transformed into various morphological species.

In 28% of healthy people in the salivary glands there are fat cells. In the glandular tissue adjacent to the tumor, they occur in 25% of cases. Morphologically fatty cells of salivary glands are similar to fatty cells of the skin in size, shape and content of lipids. They are usually located in the branches of the tubules or in the blind ends of the interlobular ducts. The location of the fat cell reflects the specific plasticity of the duct and acinus epithelium, the ability to differentiate in many directions. Fat cells can be in the salivary glands in the physiological state, but more often appear in inflammation and tumors. They are also found in the parenchyma of the salivary glands.

Light cells appear in the duct of the salivary glands in pathological conditions and tumors. They have a cell membrane and a transparent cytoplasm. A large bladder-like nucleus contains a chromatin accumulation. These cells appear separately or in groups (pleomorphic adenoma) or form large fields, as in the mucoepidermoid and acinocellular tumor. Histochemical studies have shown the presence of a large amount of glycogen in the cytoplasm. Glikogen-rich light cells have the form of a myoepithelial cell.

Only in the epithelial cells of the acini and ducts, mitoses are rare; in children in the so-called "proliferative zone" mitosis occurs, in adults they are absent. In the areas with the parenchyma affected by the gland, a partial regeneration of the regeneration takes place. The hyperplastic reaction occurs in the adjacent acinus and duct. Hypertrophy and hyperplasia of the epithelial components is especially common in inflammation. In proliferating cells, atypia and hyperplasia of glandular and stromal elements develop, imitating tumor growth.

The parenchyma, especially the large salivary glands, undergoes atrophy in elderly patients in case of chronic inflammation and other pathological processes such as hypoxia as a result of impaired blood circulation, chronic alcoholism, metabolic disorders, etc. Serous acinus of the parotid gland is most sensitive to changes leading to degeneration. This is especially true for cases of fatty atrophy, in which the glandular acini is slowly contracted and its boundaries assume vague outlines. Lipid droplets appear in the cytoplasm of secretory cells, which are replaced by lipoblasts. The ripe fat cell is surrounded by atrophied acini and gradually replaces them; Salivary glands are degenerated. The glandular cells are adjacent to the blood vessels, and the epithelium of the gland duct supports their vital functions.

Involution is the result of hyalinosis and fibrosis. There is condensation and nodulation in the gland, imitating tumor changes. As a result of the involution, the parenchyma of the gland is squeezed by proliferating fibrosis and stromal hyalinosis, atrophy. The process usually begins with the appearance of the hyalofibrous mass in the surrounding substance. Hyalinosis can be accelerated as a result of inflammation and combined with cystic degeneration of the excretory duct. The single-row epithelium of the duct flattened and slowly atrophied. The epithelium of tubules and interlobular ducts undergo squamous metaplasia.

Irradiation causes typical hyaline degeneration. These changes are characteristic of all salivary glands. Clinical observations confirm the development of malignant process in irradiated areas. The first microscopic changes in irradiated tissues are swelling of the gland and an increase in the production of mucus. Later, the salivary acinus atrophies, and the outflowing cyst expands. The serous acinus is most vulnerable. One of the most characteristic morphological changes after irradiation is the atypia of cells in the epithelium of the protocol and tissue fibrosis.