Salivary gland
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| Salivary gland | |
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| Salivary glands: #1 is Parotid gland, #2 is Submandibular gland, #3 is Sublingual gland | |
| Latin | glandulae salivariae |
The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose. 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.
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Histology [edit]
The gland is internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules.
Ducts [edit]
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).
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.
Anatomy [edit]
Parotid glands [edit]
The parotid gland is a salivary gland wrapped around the mandibular ramus in humans. It is one of a pair being the largest of the salivary glands, it secretes saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches. The secretion produced is mainly serous in nature and enters the oral cavity via Stensen's duct. It is located posterior to the mandibular ramus and in front of the mastoid process of temporal bone. This gland is 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.
Submandibular glands [edit]
The submandibular glands are a pair of glands located beneath the lower jaws, superior to the digastric muscles. The secretion produced is a mixture of both serous fluid and mucus, and enters the oral cavity via Wharton's ducts. Approximately 70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.You can usually feel this gland, as it is in the upper neck and feels like a rounded ball. It is located about two fingers above the Adam's apple (on a man) and about two inches apart under the chin.
Sublingual glands [edit]
The sublingual glands are a pair of glands located beneath the tongue, anterior to the submandibular glands. The secretion produced is mainly mucus in nature, however it is categorized as a mixed gland. Unlike the other two major glands, the ductal system of the sublingual glands do not have striated ducts, and exit from 8-20 excretory ducts. Approximately 5% of saliva entering the oral cavity come from these glands.
Minor salivary glands [edit]
There are 800-1000 minor salivary glands located throughout the oral cavity within the submucosa[1] of the oral mucosa, apart from areas including the anterior third of the hard palate, the attached gingivaand the anterior third of the dorsal surface of the tongue.[2] They are 1-2mm in diameter and unlike the other glands, they are not encapsulated by connective tissue only surrounded by it. The gland is 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 (except for Von Ebner's glands) and have many functions such as coating the oral cavity with saliva. Problems with dentures are sometimes associated with minor salivary glands.[1]
Von Ebner's glands [edit]
Von Ebner's glands are glands found in circumvallate papillae of the tongue. They secrete a serous fluid that begin lipid hydrolysis. They facilitate the perception of taste.
Innervation [edit]
Salivary glands are innervated, either directly or indirectly, by the parasympathetic and sympathetic arms of the autonomic nervous system. Both result in increased amylase output and volume flow.
- 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, while the submandibular and sublingual glands receive their parasympathetic input from the facial nerve (CN VII) via the submandibular ganglion. 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.[3] The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands.
Role in disease [edit]
- See mumps (parotiditis epidemica), Sjögren's syndrome, Mucocele, Graft versus host disease and Salivary gland neoplasm.
Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland because of cysts. Many anti-cancer treatments may impair salivary flow. Radiation therapy may cause permanent xerostomia, whereas chemotherapy may cause only temporary salivary impairment. Graft versus host disease after allogeneic bone marrow transplantation may manifest as dry mouth and many small mucoceles. Tumors of the salivary glands may occur.
A sialogram is a radiocontrast study of a salivary duct.
Saliva production may be pharmacologically stimulated by so-called sialagogues (e.g., pilocarpin, cevimeline). It can also be suppressed by so-called antisialagogues (e.g., tricyclic antidepressants, SSRI, antihypertensives, polypharmacy). [4]
The salivary glands of some species, however, are modified to produce enzymes; 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 poisonous snakes, Gila monsters, and some shrews, are modified salivary glands.[4]
See also [edit]
References [edit]
- ^ a b A.R TEN CATE, "Oral histology. Development, structure, and function".(1998), 2003, 2008|page=3|Edition=5thISBN=0-8151-2952-1
- ^ Hupp JR, Ellis E, Tucker MR (2008). Contemporary oral and maxillofacial surgery (5th ed.). St. Louis, Mo.: Mosby Elsevier. pp. 397–400. ISBN 9780323049030.
- ^ Costanzo, L. (2006). Physiology, 3rd ed. Saunders Elsevier. ISBN 10:1-4160-2320-8 Check
|isbn=value (help). - ^ a b Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 299–300. ISBN 0-03-910284-X.
External links [edit]
- Salivary Gland Disorders at intelihealth.com
- Illustration at merck.com
- Illustration at .washington.edu
- plastic/371 at eMedicine - "Parotid Tumors, Benign"
- Medical Encyclopedia Medline Plus: Salivary gland
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