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The salivary glands are three pairs of large and several hundred small glands scattered throughout the mucosa, fulfilling their function continuously. Salivary glands, because we are talking about them, perform many tasks in the human body. Do you know what types of salivary glands are and what is their structure? What are the salivary glands responsible for?
The salivary glandsare the exocrine glands responsible for the production of saliva. The body of each of us is equipped with three pairs of large salivary glands supported by several hundred tiny glands located on the entire surface of the oral and pharyngeal mucosa.
Generally speaking, the salivary gland consists of the parenchyma and the drainage ducts through which the saliva is drained.
Histologically, salivary glands are composed of secretory cells (serous or mucous) grouped into larger units, the so-called lobules. The content of the individual units goes to the medullary ducts and flows successively in ducts of increasing diameter, all the way to the main exit duct ending in the oral cavity. The large salivary glands include:
- Parotid glands- the largest salivary glands weighing about 30-40 g. They lie symmetrically on both sides of the face. The parotid gland consists of the superficial and deep parts. The boundary between the two parts is the facial nerve. The superficial layer is located posteriorly and partially on the masseter muscle and anteriorly from the ear section. The deep part is located in the mandibular fossa. The parenchyma of the salivary gland is surrounded by a connective tissue capsule, which connects to the fascia of adjacent muscles, including the masseter muscle. The salivary gland produces mainly serous content. Saliva flows down a lead tube (called the Stonon or Stensen tube) into the vestibule of the mouth. The cord runs forward along the masseter muscle, then curves medially, pierces the buccal muscle and ends at the level of the second upper molar. The salivary gland produces about 25% of resting saliva and 70% of stimulated saliva. The external carotid artery, the mandibular vein and the facial nerve run through the parenchyma of the parotid gland. There are also lymph nodes and vessels in the salivary gland.
- Submandibular glands- even glands, locatedon both sides, just below the lower edge of the mandible in the so-called submandibular triangles. They are mixed with the predominance of serous components. Saliva from this gland is drained through the Wharton duct, the outlet of which is located at the bottom of the mouth, under the tongue. The submandibular glands are responsible for the production of about 70% of saliva at rest and 25% of saliva after stimulation, e.g. with the taste of food.
- Sublingual glands- the smallest of the large salivary glands, they lie at the floor of the mouth on the mandibular-hyoid muscle just below the mucosa. They are of a mixed nature with a predominance of mucous secretions. Equipped with a discharge tube (Bartholin) that flows out with the submandibular gland tube at the bottom of the mouth.
What are the functions of salivary glands and saliva?
The primary function of salivary glands is to secrete saliva. The salivary glands produce saliva continuously. The human body produces about 1 liter of saliva in one day. Both an excessive production of saliva, called drooling, and an insufficient amount of saliva (hyposialia) can be a symptom of many diseases.
The composition of resting and stimulated saliva (released in response to stimuli such as chewing, smell, taste of food, etc.) differs. 99.5% of saliva consists of water, the remaining half percent are inorganic and organic compounds. Saliva has many functions, first of all, it facilitates the intake of food, moisturizes the food pieces, thanks to which they become easier to swallow. The enzyme in saliva, salivary amylase, is responsible for the initial stage of sugar digestion. Bactericidal substances (lysozyme, lactoferrin, sialoperoxidase system etc.) limit the growth of bacteria in the oral cavity, protecting us against harmful pathogens. Carbonate and phosphate ions act as a buffer responsible for maintaining the correct pH in the oral cavity. Saliva is also rich in other ions (including calcium and phosphates) responsible for the balance of demineralization and remineralization processes, which are key in the formation of caries.
Diseases of the salivary glands
Disorders of the function of the salivary glands may be symptoms of many systemic diseases, and may also develop only in the area of the salivary glands.
Large glands are more often affected by pathological processes. One of the diseases of the salivary glands is urolithiasis. It is classified as a non-inflammatory disease. It consists in the precipitation of mineral s alts in the ducts leading out small and large salivary glands (sometimes stones are formed in the salivary gland parenchyma). Mineral s alts accumulate in increasing amounts creating the so-called salivary stones, which initially obstruct and eventually completely block the outflow of saliva from the salivary gland. ThatDue to the structure of the discharge duct and the position of the submandibular gland, urolithiasis most often affects this gland. The presence of salivary stones is manifested by enlargement of the diseased salivary gland and pain that is particularly severe when eating food. Often in the course of urolithiasis, secondary infection of the salivary gland and development of inflammation occurs.
Other non-inflammatory diseases of the salivary glands are pathological conditions resulting from abnormal hormonal balance, metabolism disorders or disorders of the autonomic system. They are characterized by disturbances in the secretion and function of the salivary glands. Often there is enlargement of the salivary glands and their soreness, disturbance of secretion (excessive or insufficient production of saliva).
Sjögren's syndrome a disease from the group of autoimmune diseases. The etiology has not been fully understood. The essence of the disease is the formation of lymphocytic infiltrates in the parenchyma of the salivary and lacrimal glands. This leads to a gradual disappearance of the secretory activity of the glands. The disease may involve primary salivary glands or appear secondary in other systemic diseases, eg rheumatoid arthritis (RA), systemic lupus erythematosus, etc. It develops slowly and more often in women than in men. The main symptom is dry mouth (xerostomia), in addition, there may be dryness of the conjunctiva. Patients complain of "sand feeling under the eyelids". General symptoms such as malaise, muscle and joint pains, and easy fatigue are often associated.
In addition to the above-mentioned non-inflammatory diseases, conditions associated with an inflammatory reaction may develop in the salivary glands. Various factors may be responsible for them, but the most common ones are bacterial or viral infections (e.g. mumps virus). Bacterial infection often occurs in the course of salivary stones. Inflammation of the salivary glands can be divided into e.g. on: 1. Primary inflammation begins in the salivary glands. 2. Secondary, accompanying other diseases. A separate group of diseases of the salivary glands are neoplasms of the salivary glands. Both benign and malignant neoplasms are found in the tissues of the salivary glands. The neoplastic process more often affects the large salivary glands. The neoplasms associated with the salivary glands include, among others adenoma multiforme (tumor mixtus), muco-epidermal carcinoma, adenocystic carcinoma (so-called oblate).