Sublingual gland (called Capḷiṅkuval curappi in tamil) One on each side of the frenulum, lateral to the Wharton duct in the submucosal compartment, the pair of sublingual glands are positioned in the floor of the mouth, one on each side of the frenulum. These glands drain either directly into the mouth’s floor via the Rivinus ducts or indirectly via the biggest duct (Bartholin duct), which empties into the Wharton ducts.
Location and structure:
The almond-shaped sublingual glands are located on the floor of the oral cavity. They are located beneath the tongue and are bordered laterally by the mandible and medially by the tongue’s genioglossus muscle. The glands form the sublingual fossa, a shallow groove on the mandible’s medial surface.
The lingual nerve and the submandibular duct run parallel to the medial aspect of the sublingual gland.
Both sublingual glands join anteriorly to create a single mass around the lingual frenulum in a horseshoe pattern. The superior part of this U-shape generates a raised, elongate crest of mucous membrane termed the sublingual fold (plica sublingualis) (plica sublingualis).
Each sublingual fold begins on the posterolateral side of the lingual frenulum and travels anteriorly to connect the sublingual papilla at the midline.
Minor sublingual ducts (of Rivinus) drain secretions into the oral cavity, with 8-20 excretory ducts per gland, each going out into the sublingual folds. A large sublingual duct (of Bartholin) can be present in some people due to anatomical differences. This big auxiliary duct emerges from the sublingual gland’s inferior aspect and attaches to the passing submandibular duct on its medial side. Drainage then proceeds through the sublingual papilla, following the submandibular duct.
Vasculature:
The external carotid artery supplies blood via the sublingual and submental arteries, which emerge from the lingual and facial arteries, respectively.
The sublingual and submental veins drain into the lingual and facial veins, which subsequently drain into the internal jugular vein.
Innervation:
Parasympathetic and sympathetic fibres, which govern salivary secretions directly and indirectly, respectively, receive autonomic innervation to the sublingual glands. They have the same innervation as the submandibular glands.
Parasympathetic
The chorda tympani branch of the facial nerve receives parasympathetic innervation from the superior salivatory nucleus via presynaptic filaments (CN VII). The chorda tympani then connects with the mandibular nerve’s lingual branch (CNViii), before synapsing with the submandibular ganglion and suspending it by two nerve filaments.
Secretomotor fibres directly induce the gland to generate secretions, and vasodilator fibres accompany arteries to boost blood supply to the gland, making up postganglionic innervation. Saliva secretion is aided by increased parasympathetic drive.
Sympathetic
Post-synaptic vasoconstrictive fibres migrate in a plexus from the superior cervical ganglion to the internal and external carotid arteries, facial artery, and lastly the sublingual and submental arteries to enter each gland.
Increased sympathetic drive limits glandular bloodflow by vasoconstriction and lowers salivary production volume, resulting in mucus saliva.
Function:
Although the sublingual tissue is mostly a mucous gland, it is also classified as a mixed serous and mucous gland. It consists mostly of mucous acini with serous demilunes. It is the only major salivary gland that is not encased. The primary function of sublingual tissue is to produce a viscous mucinous fluid that lubricates the oral cavity and enables for swallowing, digesting, pH buffering, and dental hygiene.
The content of saliva is determined by the salivary flow rate, which varies depending on the flow rate and overall contribution of each gland. Saliva contains both organic and inorganic substances. Electrolytes, urea, and ammonia are examples of inorganic components. Immunoglobulins, enzymes, and proteins are among the organic components of saliva .Mucin is the major protein found in mucous saliva, and it lubricates and inhibits bacterial attachment to the salivary duct epithelium. This activity gives the sublingual gland antibacterial protection.
Embryology of sublingual gland:
The sublingual gland arises in the eighth week of foetal development, which is later than the other main salivary glands. It comes from epithelial buds that surround the sublingual folds on the mouth’s floor. These epithelial buds mature into cords that canalise to generate the sublingual ducts and mucous acini. When the sublingual gland is fully developed, it develops laterally to the submandibular gland before migrating to a position anterior and superior to the submandibular gland.
Histonomy of sublingual gland:
Large pyramidal mucous cells with rich pale blue vacuolated cytoplasm are found in the sublingual gland acini of rodents (Fig. 8.9). The sublingual gland lacks adrenergic innervation, unlike the submandibular and parotid glands in rodents. In humans, the acini of the sublingual gland contain a mixture of mucous and serous cells. Flattened basal nuclei and pale eosinophilic cytoplasm are found in acinar mucous cells.
Conclusion:
Any of the organs that release saliva, a fluid that moistens and softens food, into the mouth cavity of vertebrates, is known as a salivary gland.
Salivary gland secretions can be primarily serous, mucous, or mixed. Mucus is a viscous, transparent material with a slimy texture. Water and proteins, such as the digestive enzyme amylase, make up serous secretion, which is a more liquid, opalescent fluid. The glands may be specialised, releasing only one of these two chemicals, or mixed, releasing a mixture of both secretions, depending on the sorts of cells present. The presence, thought, or smell of food, as well as temperature stimulation, might stimulate secretions.