The sublingual gland is the smallest of the three major salivary glands in humans and is located below the tongue. It produces a mixed secretion consisting mainly of mucous, mucoid components. The salivary gland is divided into two sections, the glandula sublingualis major, a contiguous glandular structure, and the glandulae sublinguales minores, smaller glandular packets, each with its own exits.
What is the sublingual gland?
Salivary secretion in humans occurs via three so-called major salivary glands, which are organs in their own right, and via a number of minor salivary glands that are part of the oral mucosa. The sublingual gland is the smallest of the three major salivary glands. It consists of two areas, the glandula sublingualis major, a contiguous glandular package with a common excretory duct, and an area with several small glandular packages, the glandulae sublinguales minores, each with its own exits. The saliva produced by the sublingual glands is mainly used for storing food and facilitating its onward transport. The mucus secreted by the sublingual glands therefore contains mainly mucous, but also serous, components. The stimulation of the sublingual glandules to secrete saliva occurs via the autonomic nervous system. Parasympathetically, the sublingual glands are innervated by a branch of the seventh cranial nerve, the facial nerve.
Anatomy and structure
The sublingual gland belongs to the mixed glands, since the secreted saliva consists of a small part of serous components, but mainly of mucous components. The salivary gland is arranged in pairs below the tongue, on both sides of the lingual frenulum. The excretory ducts of the larger salivary gland complex, the sublingual gland, unite with the excretory ducts of the submandibular salivary gland and terminate on the so-called hunger wart, a papilla located immediately to the right and left of the lingual frenulum. The excretory ducts of the smaller glandular complexes of the glandulae sublinguales minores are numerous and terminate laterally of the tongue. Because saliva contains only a small proportion of serous components, the proportion of switching pieces and strip pieces is small, which in serous saliva provide electrolytic processing of the primary saliva and the necessary salt withdrawal and return. The sublingual gland – like all other salivary glands – is controlled by the autonomic nervous system. The quantitative and qualitative control of secretion is sympathetic and parasympathetic. Parasympathetic innervation occurs through lateral branches of the seventh cranial nerve via the facial nerve in a complex circuit in the nucleus salivatorius and via the submandibular ganglion. Sympathetic innervation comes from the nerve complexes originating from the spine in the cervical-thoracic vertebral junction.
Function and tasks
The main function of the sublingual gland is the secretion of saliva due to sympathetically and parasympathetically controlled stimuli and due to certain reflexes that may be triggered, for example, by the sight or smell of food. The sublingual gland, together with the other two major salivary glands, secretes about 90% of the saliva, which under normal conditions can be assumed to be 500 to 1,500 ml per day. The reduction of secretion occurs via the parasympathetic nervous system. Because the saliva of the sublingual gland contains only a small serous portion, the saliva has mainly a physical-swallowing function. During the chewing process, the gland is mechanically stimulated to release saliva. The food is moistened and can thus release flavoring substances, and onward transport to the pharyngeal region for absorption into the esophagus is enabled and facilitated. The mucous part of the saliva also fulfills an important function for the normal speech process. It enables painless and frictionless adjustments of the mouth and throat to the different sound formations and, due to its high viscosity, it prevents saliva from constantly leaking out of the mouth.The sublingual gland, in conjunction with the other two large salivary glands and the large number of small salivary glands, helps to protect the mucous membrane of the oral cavity from dehydration and bacterial infections and to remineralize the teeth after eating acidic food with a pH value below 7 and to regenerate the tooth enamel. Tooth enamel is attacked in the acidic environment and loses important minerals.
Diseases
Many disorders are possible in connection with salivary secretion from the sublingual gland, which can be caused either by diseases or dysfunctions of the gland itself or by disorders in the neuronal control of saliva production or by autoimmune reactions that attack the tissues of the gland. The most common pathological disorders and complaints are due to bacterial or viral inflammation (sialadenitis), which usually leads to painful swelling of the affected gland and to disturbances in the quantitative and qualitative secretion of saliva. An example of virally caused sialadenitis is mumps. Inflammation of the salivary glands can also be caused by tumors, irradiation or injuries with triggering of the corresponding symptoms. The quantitative and/or qualitative disorders of saliva production are called dyschilia. Insufficient production results in uncomfortably dry mouth. The symptoms of dry mouth, called xerostomia, can also be caused as adverse side effects of certain medications or by the autoimmune disease Sjögren’s syndrome. Sjögren’s syndrome is an autoimmune disease in which the immune system attacks tissue cells of the salivary and lacrimal glands. Excessive salivation, known as hypersalivation or sialorrhea, can also be pathological and lead to serious physical and psychological symptoms. Qualitatively impaired secretion of saliva can lead to the formation of salivary stones, which must be removed if they obstruct the outlet of the affected gland and impede the drainage of saliva.