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The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have 3 paired major salivary glands (parotid, submandibular and sublingual) as well hundreds of minor salivary glands.[1] Salivary glands can be classified as a serous, mucus or mixed gland.

Salivary gland
Blausen 0780 SalivaryGlands.png
Human salivary glands.
Details
System Digestive system
Identifiers
Latin Glandulae salivariae
MeSH D012469
FMA 95971
Anatomical terminology

In serous secretions, the main type of protein secreted is ptyalin(alpha-amylase), an enzyme that breaks down starch into maltose and glucose[2], whereas in mucous secretions, the main protein secreted is mucin which acts as a lubricant.[1]

Contents

StructureEdit

 
Salivary glands: #1 is Parotid gland, #2 is Submandibular gland, #3 is Sublingual gland.

The salivary glands are detailed below:

Parotid glandsEdit

The two parotid glands are major salivary glands wrapped around the mandibular ramus in humans.[3] The largest of the salivary glands, they secrete saliva to facilitate mastication and swallowing, and amylase to begin the digestion of starches.[4] It is the serous type of gland which secretes ptyalin.[5] It enters the oral cavity via the parotid duct (Stensen 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 of it since any iatrogenic lesion will result in either loss of action or strength of muscles involved in facial expression.[5] They produce 20% of the total salivary content in the oral cavity.[4] Mumps is a viral infection, caused by infection in the parotid gland.[6]

Submandibular glandsEdit

The submandibular glands (previously known as submaxillary glands) are a pair of major salivary glands located beneath the lower jaws, superior to the digastric muscles.[3] The secretion produced is a mixture of both serous fluid and mucus, and enters the oral cavity via the submandibular duct or Wharton duct.[4] Approximately 65-70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.[4] This gland can usually be felt 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 glandsEdit

The sublingual glands are a pair of major salivary glands located inferior to the tongue, anterior to the submandibular glands.[3] The secretion produced is mainly mucous in nature; however, it is categorized as a mixed gland.[5] 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.[5] Approximately 5% of saliva entering the oral cavity comes from these glands.[4]

Minor salivary glandsEdit

There are 800 to 1,000 minor salivary glands located throughout the oral cavity within the submucosa[7] 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.[8] 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 there is dry mouth present (see further discussion).[7] The minor salivary glands are innervated by the seventh cranial or facial nerve.[8]

Von Ebner's glandsEdit

Von Ebner's glands are glands 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.[7] 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 supplyEdit

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. In contrast, sympathetic stimulation produces either a small flow, which is rich in protein, or no flow at all.[9]

  • Parasympathetic innervation to the salivary glands is carried via cranial nerves. The parotid gland receives its parasympathetic input from the glossopharyngeal nerve (CN IX) via the otic ganglion,[10] while the submandibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion.[11] These nerves release acetylcholine and substance P, which activate the IP3 and DAG pathways respectively.
  • Direct sympathetic innervation of the salivary glands takes place via preganglionic nerves in the thoracic segments T1-T3 which synapse in the superior cervical ganglion with postganglionic neurons that release norepinephrine, which is then received by β-adrenergic receptors on the acinar and ductal cells of the salivary glands, leading to an increase in cyclic adenosine monophosphate (cAMP) levels and the corresponding increase of saliva secretion. Note that in this regard both parasympathetic and sympathetic stimuli result in an increase in salivary gland secretions.[12] The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands.

MicroanatomyEdit

The gland is internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules.

AciniEdit

Secretory cells are found in a group, or acinus (plural, acini). 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.[13]

DuctsEdit

In the duct system, the lumina are formed by intercalated ducts, which in turn join to form striated ducts. These drain into ducts situated between the lobes of the gland (called interlobar ducts or secretory ducts). These are found on most major and minor glands (exception may be the sublingual gland).[13]

All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The saliva that salivary glands release is quickly inactivated in the stomach by the acid that is present there but the saliva also contains enzymes that are actually activated by the acid.

Gene and protein expressionEdit

About 20,000 protein coding genes are expressed in human cells and 60% of these genes are expressed in normal, adult salivary glands[14][15]. 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 statherin, all of major importance for specific characteristics of saliva.

DevelopmentEdit

AgingEdit

Aging of salivary glands show some structural changes:[16][17][18]

  • Decrease in volume of acinar tissue
  • Increase in fibrous tissue
  • Increase in adipose tissue
  • Ductal hyperplasia and dilation [16]

In addition to that, there would be some changes in salivary contents:

  • Decrease in concentration of secretory IgA [16]
  • Decrease in the amount of mucin

However, there is no overall change in the amount of saliva secreted.

FunctionEdit

Salivary glands secrete saliva which has many benefits for the oral cavity and health in general. These benefits include:

  • protection
  • buffering
  • pellicle formation
  • maintenance of tooth integrity
  • antimicrobial action
  • tissue repair
  • digestion
  • taste[19]

Saliva contains a collection of proteins which act defensively. Some proteins such as salivary immunoglobulins and salivary chaperokine HSP70/HSPA, are involved in both innate and acquired immune activation.[20]

While present in low proportions, their effects are cumulative, resulting in a secure molecular defence network of the oral cavity. In certain areas of the oral cavity, such as mucosal surfaces, periodontal sulcus, and oral wounds and ulcers, the concentrations seem to be greater.[20]

Salivary proteins have 4 main defence mechanisms:

  • microbial agglutination and/or surface exclusion. For example; peptides which bind to the bacteria and also bind to either oral mucosa or to each other.
  • The second network may be expected to be responsible for lysis of microbial membranes. This network primarily targets bacteria, and are likely to include salivary cationic peptides and lysozyme.
  • The third and fourth networks may be responsible for antifungal and antiviral properties of the saliva, including antifungal/antiviral properties respectively
  • immune regulatory network of salivary proteins may also be expected[20]

Clinical significanceEdit

 
Micrograph of chronic inflammation of the salivary gland sialadenitis).

A sialogram is a radiocontrast study of a salivary duct that may be used to investigate its function and for diagnosing Sjogren's Syndrome. [21]

A salivary calculus may cause blockage of the ducts, causing pain and swelling of the gland. This is called a Sialolithiasis and are most commonly found in the submandibular ducts. [22]

Saliva production may be pharmacologically stimulated by sialagogues such as pilocarpine and cevimeline.[23] It can also be suppressed by so-called antisialagogues such as tricyclic antidepressants, SSRIs, antihypertensives, and polypharmacy.[24] A Cochrane review found there was no strong evidence that topical therapies are effective in relieving the symptom of dry mouth.[25]

Cancer treatments including chemotherapy and radiation therapy may impair salivary flow.[26][27] Radiation therapy may cause permanent hyposalivation due to injury to the oral mucosa containing the salivary glands, resulting in dry mouth or xerostomia, whereas chemotherapy may cause only temporary salivary impairment.[26][27]

Graft versus host disease after allogeneic bone marrow transplantation may manifest as dry mouth and many small mucoceles. [28] Tumours of the salivary glands may occur, including mucoepidermoid carcinoma.[29]

Other animalsEdit

The salivary glands of some species however, are modified to produce proteins; salivary amylase is found in many, but by no means all, bird and mammal species (including humans, as noted above). Furthermore, the venom glands of venomous snakes (colloquially called poisonous snakes), Gila monsters, and some shrews, are modified salivary glands.[24] In other organisms such as insects, salivary glands are often used to produce biologically important proteins like silk or glues, and fly salivary glands contain polytene chromosomes that have been useful in genetic research. [30]

See alsoEdit

ReferencesEdit

  1. ^ a b Edgar, Michael; Dawes, Colin; O'Mullane, Denis, eds. (2012). Saliva and oral health (4th ed.). Little Steine, Hill Farm Lane, Duns Tew, OX25 6JH: Stephen Hancocks Limited. p. 1. ISBN 978-0-9565668-3-6. 
  2. ^ Martini, Frederic H.; Nath, Judi L.; Bartholomew, Edwin (2012). Fundamentals of anatomy & physiology (9th ed.). 1301 Sansome St., San Francisco, CA 94111: Pearson Benjamin Cummings. 
  3. ^ a b c Bialek EJ, Jakubowski W, Zajkowski P, Szopinski KT, Osmolski A (2006). "US of the major salivary glands: anatomy and spatial relationships, pathologic conditions, and pitfalls". Radiographics : a Review Publication of the Radiological Society of North America, Inc. 26 (3): 745–63. doi:10.1148/rg.263055024. PMID 16702452. 
  4. ^ a b c d e Nanci A (2018). Ten Cate's Oral Histology: Development, Structure, and Function (ninth ed.). ISBN 978-0-323-48524-1. 
  5. ^ a b c d Holmberg KV, Hoffman MP (2014). "Anatomy, biogenesis and regeneration of salivary glands". Monographs in Oral Science. 24: 1–13. doi:10.1159/000358776. PMC 4048853 . PMID 24862590. 
  6. ^ Hviid A, Rubin S, Mühlemann K (2008). "Mumps". Lancet (London, England). 371 (9616): 932–44. doi:10.1016/S0140-6736(08)60419-5. PMID 18342688. 
  7. ^ a b c Nanci A (2013). Ten Cate's Oral Histology: Development, Structure, and Function (8th ed.). St. Louis, Mo.: Elsevier. pp. 275–65. ISBN 978-0-323-07846-7. 
  8. ^ a b Herring MJ, Fehrenbach SW (2012). Illustrated Anatomy of the Head and Neck (4th ed.). St. Louis, Mo.: Elsevier/Saunders. ISBN 978-1-4377-2419-6. 
  9. ^ Ekström J (1989). "Autonomic control of salivary secretion". Proceedings of the Finnish Dental Society. Suomen Hammaslaakariseuran Toimituksia. 85 (4-5): 323–31; discussion 361–3. PMID 2699762. 
  10. ^ Frommer J (1977). "The human accessory parotid gland: its incidence, nature, and significance". Oral Surgery, Oral Medicine, and Oral Pathology. 43 (5): 671–6. PMID 266146. 
  11. ^ Ishizuka K, Oskutyte D, Satoh Y, Murakami T (2010). "Multi-source inputs converge on the superior salivatory nucleus neurons in anaesthetized rats". Autonomic Neuroscience : Basic & Clinical. 156 (1-2): 104–10. doi:10.1016/j.autneu.2010.03.014. PMID 20435522. 
  12. ^ Costanzo L (2009). Physiology (3rd ed.). Saunders Elsevier. ISBN 978-1-4160-2320-3. 
  13. ^ a b Bath-Balogh M, Fehrenbach M (2011). Illustrated Dental Embryology, Histology, and Anatomy. Elsevier. p. 132. ISBN 978-1-4377-2934-4. 
  14. ^ "The human proteome in salivary gland - The Human Protein Atlas". www.proteinatlas.org. Retrieved 2017-09-22. 
  15. ^ Uhlén M, Fagerberg L, Hallström BM, Lindskog C, Oksvold P, Mardinoglu A, et al. (January 2015). "Proteomics. Tissue-based map of the human proteome". Science. 347 (6220): 1260419. doi:10.1126/science.1260419. PMID 25613900. 
  16. ^ a b c Vissink A, Spijkervet FK, Van Nieuw Amerongen A. "Aging and saliva: a review of the literature". Special Care in Dentistry. 16 (3): 95–103. PMID 9084322. 
  17. ^ Kim SK, Allen ED (June 1994). "Structural and functional changes in salivary glands during aging". Microscopy Research and Technique. 28 (3): 243–53. doi:10.1002/jemt.1070280308. PMID 8068986. 
  18. ^ Kim SK, Allen ED (June 1994). "Structural and functional changes in salivary glands during aging". Microscopy Research and Technique. 28 (3): 243–53. doi:10.1002/jemt.1070280308. PMID 8068986. 
  19. ^ Nanci A (2003). Ten Cate's oral histology: development, structure, and function (6th ed.). St. Louis: Mosby. pp. 300–1. ISBN 978-0-323-01614-8. 
  20. ^ a b c Fábián TK, Hermann P, Beck A, Fejérdy P, Fábián G (2 April 2012). "Salivary defense proteins: their network and role in innate and acquired oral immunity". International Journal of Molecular Sciences. 13 (4): 4295–320. doi:10.3390/ijms13044295. PMID 22605979.    This article contains quotations from this source, which is available under the Creative Commons Attribution 3.0 Unported (CC BY 3.0) license.
  21. ^ Rastogi R, Bhargava S, Mallarajapatna GJ, Singh SK (October 2012). "Pictorial essay: Salivary gland imaging". The Indian Journal of Radiology & Imaging. 22 (4): 325–33. doi:10.4103/0971-3026.111487. PMC 3698896 . PMID 23833425. 
  22. ^ Rzymska-Grala I, Stopa Z, Grala B, Gołębiowski M, Wanyura H, Zuchowska A, Sawicka M, Zmorzyński M (July 2010). "Salivary gland calculi - contemporary methods of imaging". Polish Journal of Radiology. 75 (3): 25–37. PMC 3389885 . PMID 22802788. 
  23. ^ Wolff A, Joshi RK, Ekström J, Aframian D, Pedersen AM, Proctor G, Narayana N, Villa A, Sia YW, Aliko A, McGowan R, Kerr AR, Jensen SB, Vissink A, Dawes C (March 2017). "A Guide to Medications Inducing Salivary Gland Dysfunction, Xerostomia, and Subjective Sialorrhea: A Systematic Review Sponsored by the World Workshop on Oral Medicine VI". Drugs in R&D. 17 (1): 1–28. doi:10.1007/s40268-016-0153-9. PMC 5318321 . PMID 27853957. 
  24. ^ a b Romer AS, Parsons TS (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 299–300. ISBN 0-03-910284-X. 
  25. ^ Furness, Susan; Worthington, Helen; Bryan, Gemma; Birchenough, Sarah; McMillan, Roddy (7 December 2011). "Interventions for the management of dry mouth: topical therapies". Cochrane Library. Retrieved 19 February 2018. 
  26. ^ a b Furness S, Worthington HV, Bryan G, Birchenough S, McMillan R (December 2011). "Interventions for the management of dry mouth: topical therapies". The Cochrane Database of Systematic Reviews (12): CD008934. doi:10.1002/14651858.cd012744/epdf. PMID 22161442. 
  27. ^ a b Riley P, Glenny AM, Hua F, Worthington HV (July 2017). "Pharmacological interventions for preventing dry mouth and salivary gland dysfunction following radiotherapy". The Cochrane Database of Systematic Reviews. 7: CD012744. doi:10.1002/14651858.CD012744. PMID 28759701. 
  28. ^ Ogawa Y, Okamoto S, Wakui M, Watanabe R, Yamada M, Yoshino M, Ono M, Yang HY, Mashima Y, Oguchi Y, Ikeda Y, Tsubota K (October 1999). "Dry eye after haematopoietic stem cell transplantation". The British Journal of Ophthalmology. 83 (10): 1125–30. doi:10.1136/bjo.83.10.1125. PMID 10502571. 
  29. ^ Nance MA, Seethala RR, Wang Y, Chiosea SI, Myers EN, Johnson JT, Lai SY (October 2008). "Treatment and survival outcomes based on histologic grading in patients with head and neck mucoepidermoid carcinoma". Cancer. 113 (8): 2082–9. doi:10.1002/cncr.23825. PMC 2746751 . PMID 18720358. 
  30. ^ Sehnal F, Sutherland T (2008). "Silks produced by insect labial glands". Prion. 2 (4): 145–53. PMC 2658764 . PMID 19221523. 

External linksEdit