The parotid gland is paired and is the largest salivary gland in the human body. Topographically, the parotid gland is bounded by the external auditory canal and the mandible. The entire organ is encased in a layer of connective tissue called the parotid lobe.
What is the parotid gland?
The parotid gland is a purely serous bodily gland, histologically showing connective tissue, septa and wide excretory ducts through which the saliva formed is secreted into the oral cavity. A closer microscopic look at the cells of the parotid gland reveals an increased number of mitochondria. Since these are the power plants of a cell, anatomists assume an increased metabolic rate in the cells of the parotid gland. With increasing age, fat cells are also found in the parotid gland, and the function of saliva production is then correspondingly reduced, which in turn can be the breeding ground for diseases of the parotid gland. Together with the other two large cephalic glands, the submandibular and sublingual glands, the parotid gland produces about 90 percent of human saliva. In the course of 24 hours, about 1000 to 1550 milliliters of salivary fluid are produced. This corresponds to a secretion rate of 0.6 to 1.1 milliliters of saliva per minute.
Anatomy and structure
The salivary-secreting organ functional cells of the parotid gland are composed of highly prismatic squamous epithelium. In addition to the typical connective tissue capsule, the gland is permeated by lymphoid follicles, ganglia, nerves, and blood vessels. Like the other head glands, the parotid gland is sympathetically innervated. All 3 salivary glands of the human body have an almost identical histological structure. Thus, there is no unique histologic identifying feature of the parotid gland. The ductal system of the parotid gland is also called the acini. The acini open to various exit sites in the mouth through which saliva flows. The excretory ducts are surrounded by nerve fibers and lymphatic and blood vessels. The sublingual and mandibular salivary glands produce a predominantly mucilaginous secretion. In contrast, the secretion of the parotid gland is almost watery in consistency.
Function and tasks
The sole function of the parotid gland is the production of saliva. Conjectures that the parotid gland may also be a hormonal organ have not been confirmed. Through the excretory duct system, the saliva produced is continuously delivered to individual, solitary glands within the entire mucosa of the pharynx, oral cavity and lips. Saliva production may cease completely only in the event of disease. Salivary secretion from the parotid gland is increased up to fivefold over normal production during eating or other irritation of the sympathetic nerve. The least amount of saliva is produced at night when at rest. The main component of aqueous saliva from the parotid gland is water; in addition, saliva contains various electrolytes, proteins and enzymes. Salivary enzymes primarily serve to initiate the digestion process of complex sugar molecules such as starch. In addition, simple proteins can be broken down by the so-called proteases of the saliva and thus prepared for further digestion in the stomach. Solid food is liquefied by saliva and thus makes the swallowing process much easier. In addition, saliva also has a certain protective and defensive function. This is because saliva is important for cleaning the sensitive mucous membrane surfaces of the mouth and throat. Saliva is also important for maintaining the health of the tooth substance, because saliva neutralizes harmful acids and hardens the tooth enamel with dissolved minerals. Substances foreign to the body, for example viruses, heavy metals or antibiotics, are demonstrably eliminated via saliva.
Diseases and ailments
Acute and chronic diseases can occur at the parotid gland, which are almost always based on an inflammatory process. If the parotid gland is inflamed, the doctor refers to it as parotitis. Parotitis can be caused by bacteria, viruses or pathogenic fungi. The best known inflammation of the parotid gland is parotitis epidemica, popularly known as mumps, a childhood disease. This viral inflammation can only be treated symptomatically and usually heals without consequences after 2 weeks.In rare cases, however, severe complications occur, such as the dreaded mumps orchitis. This testicular inflammation can cause absolute sterility in men. Other parotitides occur more frequently after the age of 50 and are an expression of disturbed fluid balance. In addition, parotid stone disease is a clinically relevant phenomenon. Patients with stones in the parotid gland are more prone to inflammation due to this drainage obstruction. Larger salivary stones in the parotid gland must be surgically removed. There is a tendency for increased formation of salivary stones with chronic disease progression. The risk of inflammation and stone formation of the salivary glands can be minimized by sufficient fluid intake, careful oral hygiene, and avoidance of alcohol and nicotine. In older age, benign or malignant tumors of the parotid gland may also occur.
