The paired submandibular glands (historically known as submaxillary glands) are major salivary glands located beneath the floor of the mouth. They each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimulation their contribution decreases in proportion as the parotid secretion rises to 50%. The average length of the normal human submandibular salivary gland is approximately 27mm, while the average width is approximately 14.3mm.

Structure

Lying superior to the

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellie ...

s, each submandibular gland is divided into superficial and deep lobes, which are separated by the

mylohyoid muscle The mylohyoid muscle or diaphragma oris is a paired muscle of the neck. It runs from the mandible to the hyoid bone, forming the floor of the oral cavity of the mouth. It is named after its two attachments near the molar teeth. It forms the floor ...

: * The superficial lobe comprises most of the gland, with the mylohyoid muscle runs under it * The deep lobe is the smaller part Secretions are delivered into the

submandibular duct The submandibular duct or Wharton duct or submaxillary duct, is one of the salivary excretory ducts. It is about 5 cm. long, and its wall is much thinner than that of the parotid duct. It drains saliva from each bilateral submandibular gland and s ...

on the deep portion after which they hook around the posterior edge of the mylohyoid muscle and proceed on the superior surface laterally. The excretory ducts are then crossed by the lingual nerve, and ultimately drain into the sublingual caruncles – small prominences on either side of the

lingual frenulum The frenulum of tongue or tongue web (also lingual frenulum or frenulum linguæ; also fraenulum) is a small fold of mucous membrane extending from the floor of the mouth to the midline of the underside of the tongue. Development The tongue start ...

along with the major

sublingual duct The excretory ducts of the sublingual gland are from eight to twenty in number. Of the smaller sublingual ducts (ducts of Rivinus), some join the submandibular duct; others open separately into the mouth, on the elevated crest of mucous membrane (p ...

. The gland can be bilaterally palpated (felt) inferior and posterior to the body of the mandible, moving inward from the inferior border of the mandible near its angle with the head tilted forwards.

Microanatomy

Lobes contain smaller lobules, which contain

adenomere An adenomere is the functional unit in a developing gland. The glands include the salivary and lacrimal glands. Adenomeres are secretory sublobular units having a centrally located collecting duct that connects with postcapillary venules; and is a ...

s, the secretory units of the gland. Each adenomer contains one or more

acini An acinus (; plural, acini; adjective, acinar or acinous) refers to any cluster of cells that resembles a many-lobed "berry," such as a raspberry ('' acinus'' is Latin for "berry"). The berry-shaped termination of an exocrine gland, where the ...

, or alveoli, which are small clusters of cells that secrete their products into a duct. The acini of each adenomere are composed of either

serous In physiology, serous fluid or serosal fluid (originating from the Medieval Latin word ''serosus'', from Latin ''serum'') is any of various body fluids resembling serum, that are typically pale yellow or transparent and of a benign nature. The fl ...

or mucous cells, with serous adenomeres predominating. Some mucous adenomeres may also be capped with a

serous demilune Serous demilunes, also known as Crescents of Giannuzzi or Demilunes of Heidenhain, are cellular formations in the shape of a half-moon (hence the name "demilune") on some salivary glands. Serous demilunes are the serous cells at the distal end of ...

, a layer of lysozyme-secreting serous cells resembling a half moon. Like other

exocrine gland Exocrine glands are glands that secrete substances on to an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, prostate and mucous. Exocrine glands are one of two ...

s, the submandibular gland can be classified by the microscopic anatomy of its secretory cells and how they are arranged. Because the glands are branched, and because the tubules forming the branches contain secretory cells, submandibular glands are classified as branched tubuloacinar glands. Further, because the secretory cells are of both serous and mucous types, the submandibular gland is a mixed gland, and though most of the cells are serous, the exudate is chiefly mucous. It has long striated ducts and short intercalated ducts.Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 135 The secretory acinar cells of the submandibular gland have distinct functions. The mucous cells are the most active and therefore the major product of the submandibular glands is saliva which is mucoid in nature. Mucous cells secrete mucin which aids in the lubrication of the food bolus as it travels through the esophagus. In addition, the serous cells produce salivary amylase, which aids in the breakdown of starches in the mouth. The submandibular gland's highly active acini account for most of the salivary volume. The parotid and sublingual glands account for the remaining.

Blood supply

The gland receives its blood supply from the facial and lingual arteries. The gland is supplied by sublingual and submental arteries and drained by common facial and lingual veins.

Lymphatic drainage

The lymphatics from submandibular gland first drain into submandibular lymph nodes and subsequently into jugulo - digastric lymph nodes.

Nerve supply

Their secretions, like the secretions of other salivary glands, are regulated ''directly'' by the

parasympathetic nervous system The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of ...

and ''indirectly'' by the

sympathetic nervous system The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of th ...

. * ''Parasympathetic'' innervation to the submandibular glands is provided by the superior salivatory nucleus via the chorda tympani, a branch of the facial nerve, that becomes part of the

trigeminal nerve In neuroanatomy, the trigeminal nerve ( lit. ''triplet'' nerve), also known as the fifth cranial nerve, cranial nerve V, or simply CN V, is a cranial nerve responsible for sensation in the face and motor functions such as biting and chewin ...

's lingual nerve prior to synapsing on the submandibular ganglion. Increased parasympathetic activity promotes the secretion of saliva. * The sympathetic nervous system regulates submandibular secretions through

vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessel ...

of the arteries that supply it. Increased sympathetic activity reduces glandular bloodflow, thereby decreasing the volume of fluid in salivary secretions, producing an

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

rich

mucous Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

saliva. Nevertheless, direct stimulation of sympathetic nerves will cause an increase in salivary enzymatic secretions. In sum, the volume decreases, but the secretions are increased by parasympathetic and sympathetic innervation.

Development

The submandibular salivary glands develop later than the parotid glands and appear late in the sixth week of prenatal development. They develop bilaterally from epithelial buds in the sulcus surrounding the sublingual folds on the floor of the primitive mouth. Solid cords branch from the buds and grow posteriorly, lateral to the developing tongue. The cords of the submandibular gland later branch further and then become canalized to form the ductal part. The submandibular gland acini develop from the cords’ rounded terminal ends at 12 weeks, and secretory activity via the submandibular duct begins at 16 weeks. Growth of the submandibular gland continues after birth with the formation of more acini. Lateral to both sides of the tongue, a linear groove develops and closes over to form the submandibular duct.

Function

The submandibular gland releases a host of factors which regulate systemic inflammatory responses and modulate systemic immune and inflammatory reactions. Early work in identifying factors that played a role in the cervical sympathetic trunk-submandibular gland (CST-SMG) axis lead to the discovery of a seven

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

, called the submandibular gland peptide-T. SGP-T was demonstrated to have biological activity and thermoregulatory properties related to endotoxin exposure. SGP-T, an isolate of the submandibular gland, demonstrated its immunoregulatory properties and potential role in modulating the CST-SMG axis, and subsequently was shown to play an important role in the control of inflammation.

Clinical significance

Relative incidence of submandibular tumors

The submandibular gland accounts for 80% of all salivary duct calculi (salivary stones or sialolith), possibly due to the different nature of the saliva that it produces and the tortuous travel of the submandibular duct to its ductal opening for a considerable upward distance. The submandibular gland is one of the major three glands that provide the mouth with

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...

. The two other types of salivary glands are parotid and

sublingual Sublingual (abbreviated SL), from the Latin for "under the tongue", refers to the pharmacological route of administration by which substances diffuse into the blood through tissues under the tongue. The sublingual glands receive their prima ...

glands.

Additional images

File:Gray177.png, Mandible. Inner surface. Side view. File:Gray778.png, Distribution of the maxillary and mandibular nerves, and the submaxillary ganglion. File:WVSOM Submandibular Gland.JPG, Mucus cell are identifiable by the lack of color in their cytoplasm, while serosal cells have a basophilic color. File:SubmandInflaMark.png, Submandibular gland inflammation as seen on ultrasound

Dissection images

File:Submandibular gland.jpg, Submandibular gland File:Slide2a.JPG, Submandibular gland File:Slide1b.JPG, Submandibular gland lateral view File:Slide1c.JPG, Submandibular gland File:Slide1d.JPG, Submandibular gland - right view File:Slide1e.JPG, Submandibular gland - frontal view File:Slide5g.JPG, Submandibular gland File:Slide1EBA.JPG, Muscles, arteries and nerves of neck.Newborn dissection. File:Slide1EBAB.JPG, Muscles, arteries and nerves of neck.Newborn dissection. File:Slide2deded.JPG, Muscles, nerves and arteries of neck.Deep dissection. Anterior view. File:Anterior region of neck1.JPG, Submandibular gland

References

External links

Histology at usc.edu
* - "Anterior Triangle of the Neck: Nerves and Vessels of the Carotid Triangle" * - "Oral Cavity: The Submandibular Gland and Duct" * () * * Salivary gland cancer from American Cancer Society at http://www.cancer.org/cancer/salivaryglandcancer/detailedguide/salivary-gland-cancer-what-is-salivary-gland-cancer {{Authority control Glands of mouth