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The salivary glands in many including are that produce saliva through a system of ducts. Humans have three paired major salivary glands (Parotid gland, submandibular, and sublingual gland), as well as hundreds of minor salivary glands. (2025). 9780956566836, Stephen Hancocks. ISBN 9780956566836 Salivary glands can be classified as Serous gland, Mucous gland, or seromucous gland (mixed).
In Serous fluid, the main type of protein secreted is alpha-amylase, an enzyme that breaks down starch into maltose and glucose,
In humans, 1200 to 1500 ml of saliva are produced every day. The secretion of saliva (salivation) is mediated by parasympathetic stimulation; acetylcholine is the active neurotransmitter and binds to muscarinic receptors in the glands, leading to increased salivation.
A proposed fourth pair of salivary glands, the tubarial glands, were first identified in 2020. They are named for their location, being positioned in front of and over the torus tubarius. However, this finding from one study is yet to be confirmed.
All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The released saliva is quickly inactivated in the stomach by the acid that is present, but saliva also contains enzymes that are actually activated by stomach acid.
In addition, changes occur in salivary contents:
Salivary gland dysfunction is either a reduced (hyposalivation), or an increased (hypersalivation) production of saliva. Xerostomia, the symptom of dry mouth is often caused by hyposalivation and is associated with significant impairment of quality of life. Following radiotherapy of the head and neck region, salivary gland dysfunction is a predictable side-effect. Saliva production may be pharmacologically stimulated by such as pilocarpine and cevimeline. It can also be suppressed by so-called such as tricyclic antidepressants, , antihypertensives, and polypharmacy.
Cancer treatments including chemotherapy and radiation therapy may impair salivary flow. Radiotherapy can cause permanent hyposalivation due to injury to the oral mucosa containing the salivary glands, resulting in xerostomia, whereas chemotherapy may cause only temporary salivary impairment. Surgical removal of benign or malignant lesions may also impair function.
Graft-versus-host disease after allogeneic bone marrow transplantation may manifest as dry mouth and many small oral mucocele. Salivary gland tumours may occur, including mucoepidermoid carcinoma, a cancer.
(2025). 9780321709332, Pearson Benjamin Cummings. ISBN 9780321709332 whereas in Mucus, the main protein secreted is mucin, which acts as a lubricant.
Structure
Parotid glands
The two are major salivary glands wrapped around the mandibular ramus in humans. These are largest of the salivary glands, secreting saliva to facilitate mastication and swallowing, and amylase to begin the digestion of starches. (2025). 9780323485241, Elsevier. ISBN 9780323485241 It is the serous type of gland which secretes alpha-amylase (also known as ptyalin). (2025). 9783318025958 ISBN 9783318025958 It enters the oral cavity via the parotid duct. The glands are located posterior to the mandibular ramus and anterior to the mastoid process of the temporal bone. They are clinically relevant in dissections of facial nerve branches while exposing the different lobes, since any iatrogenic lesion will result in either loss of action or strength of muscles involved in facial expression. They produce 25% of the total salivary content in the oral cavity. Mumps is a viral disease, caused by infection in the parotid gland.
Submandibular glands
The submandibular glands (previously known as submaxillary glands) are a pair of major salivary glands located beneath the lower jaws, superior to the . The secretion produced is a mixture of both serous fluid and mucus, and enters the oral cavity via the submandibular duct or Wharton duct. Around 70% of saliva in the oral cavity is produced by the submandibular glands, though they are much smaller than the parotid glands. This gland can usually be felt via palpation of the neck, as it is in the superficial cervical region and feels like a rounded ball. It is located about two fingers above the Adam's apple (laryngeal prominence) and about two inches apart under the chin.
Sublingual glands
The sublingual glands are a pair of major salivary glands located inferior to the tongue, anterior to the submandibular glands. The secretion produced is mainly mucus in nature, but it is categorized as a mixed gland. Unlike the other two major glands, the ductal system of the sublingual glands does not have intercalated ducts and usually does not have striated ducts, either, so saliva exits directly from 8-20 excretory ducts known as the Rivinus ducts. About 5% of saliva entering the oral cavity comes from these glands.
Tubarial salivary glands
The tubarial glands are suggested as a fourth pair of salivary glands situated posteriorly in the nasopharynx and nasal cavity, predominantly with mucous glands, and its ducts opening into the dorsolateral pharyngeal wall. The glands were unknown until September 2020, when they were discovered by a group of Dutch scientists using prostate-specific membrane antigen PET-CT. This discovery may explain Xerostomia after radiotherapy despite the avoidance of the three major glands. However, these findings from just one study need to be confirmed. On the other hand, an interdisciplinary group of scientists disagree with this new discovery. They believe that an accumulation of minor salivary glands has been described. The researchers examined the scans and confirmed the glandular tissue through dissection of cadavers, proposing that this structure could constitute a previously unrecognized major salivary gland. Their findings raised clinical interest, particularly in radiation oncology, as damage to these glands during radiotherapy for head and neck cancers might contribute to xerostomia (dry mouth), even when the known major salivary glands are spared.
Minor salivary glands
Around 800 to 1,000 minor salivary glands are located throughout the oral cavity within the submucosa (2025). 9780323078467, Elsevier. ISBN 9780323078467 of the oral mucosa in the tissue of the buccal, labial, and lingual mucosa, the soft palate, the lateral parts of the hard palate, and the floor of the mouth or between muscle fibers of the tongue. (2025). 9781437724196, Elsevier/Saunders. ISBN 9781437724196 They are 1 to 2 mm in diameter and unlike the major glands, they are not encapsulated by connective tissue, only surrounded by it. The gland has usually a number of acini connected in a tiny lobule. A minor salivary gland may have a common excretory duct with another gland, or may have its own excretory duct. Their secretion is mainly mucous in nature and have many functions such as coating the oral cavity with saliva. Problems with dentures are sometimes associated with minor salivary glands if dry mouth is present. The minor salivary glands are innervated by the Facial nerve.
Von Ebner's glands
Von Ebner's glands are found in a trough circling the circumvallate papillae on the dorsal surface of the tongue near the terminal sulcus. They secrete a purely serous fluid that begins lipid hydrolysis. They also facilitate the perception of taste through secretion of digestive enzymes and proteins.
The arrangement of these glands around the circumvallate papillae provides a continuous flow of fluid over the great number of taste buds lining the sides of the papillae, and is important for dissolving the food particles to be tasted.
Nerve supply
Salivary glands are innervated, either directly or indirectly, by the parasympathetic and sympathetic arms of the autonomic nervous system. Parasympathetic stimulation evokes a copious flow of saliva.
(2025). 9781416023203, Saunders Elsevier. ISBN 9781416023203 the difference lies on the composition of this saliva, once sympathetic stimulus results particularly in the increase of amylase secretion, which is produced by serous glands. The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the that supply the glands, resulting in vasoconstriction through the activation of α1 adrenergic receptors, lessening the saliva's water content.
Microanatomy
The gland is internally divided into lobules. and enter the glands at the hilum and gradually branch out into the lobules.
Acini
Secretory cells are found in a group, or acinus. Each acinus is located at the terminal part of the gland connected to the ductal system, with many acini within each lobule of the gland. Each acinus consists of a single layer of cuboidal epithelial cells surrounding a lumen, a central opening where the saliva is deposited after being produced by the secretory cells. The three forms of acini are classified in terms of the type of epithelial cell present and the secretory product being produced - serous, mucoserous, and mucous. (2025). 9780443104244, Elsevier. ISBN 9780443104244
Ducts
In the duct system, the lumina are formed by intercalated ducts, which in turn join to form . These drain into ducts situated between the lobes of the gland (called interlobular ducts or secretory ducts). These are found on most major and minor glands (exception may be the sublingual gland).
Gene and protein expression
About 20,000 protein-coding genes are expressed in human cells and 60% of these genes are expressed in normal, adult salivary glands. Less than 100 genes are more specifically expressed in the salivary gland. The salivary gland specific genes are mainly genes that encode for secreted proteins and compared to other organs in the human body; the salivary gland has the highest fraction of secreted genes. The heterogeneous family of proline-rich, human salivary glycoproteins, such as PRB1 and PRH1, are salivary gland-specific proteins with highest level of expression. Examples of other specifically expressed proteins include the digestive amylase enzyme AMY1A, the mucin MUC7 and STATH, all of major importance for specific characteristics of saliva.
Aging
Aging of salivary glands shows some structural changes, such as:
Function
Salivary glands secrete saliva, which has many benefits for the oral cavity and health in general. The knowledge of normal salivary flow rate (SFR) is extremely important when treating dental patients. These benefits include:
The proteins (statherin and proline-rich proteins) within the salivary pellicle inhibit demineralization and promote remineralization by attracting calcium ions.
(2025). 9780323016148, Mosby. ISBN 9780323016148 Saliva acts as a solvent in which solid particles can dissolve and enter the taste buds through oral mucosa located on the tongue. These taste buds are found within foliate and circumvallate papillae, where minor salivary glands secrete saliva.
Clinical significance
A sialolithiasis is a salivary stone that may cause blockage of the ducts, most commonly the submandibular ducts, causing pain and swelling of the gland.
(1977). 9780039102845, Holt-Saunders International. ISBN 9780039102845 A Cochrane review found there was no strong evidence that topical therapies are effective in relieving the symptoms of dry mouth.
Imaging
A sialogram is a radiocontrast study of a salivary duct that may be used to check its function, and for diagnosing Sjögren syndrome.
Other animals
The salivary glands of some species are modified to produce proteins; salivary amylase is found in many bird and mammal species (including humans, as noted above). Furthermore, the venom Venom glands of , , and some , are actually modified salivary glands. In other organisms such as insecta, salivary glands are often used to produce biologically important proteins such as silk or glues, whilst fly salivary glands contain polytene chromosomes that have been useful in genetics research.
See also
External links
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