Salivary gland

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Salivary gland
Image:Illu quiz hn 02.jpg
Salivary glands: #1 is Parotid gland, #2 is Submandibular gland, #3 is Sublingual gland
Latin	glandulae salivariae
MeSH	Salivary+Glands
Dorlands/Elsevier	g_06/12391916

The salivary glands are exocrine glands that produce saliva, which keeps the mouth and other parts of the digestive system moist. Saliva also helps break down carbohydrates (with salivary amylase, formerly known as ptyalin) and lubricates the passage of food down from the oropharynx to the stomach.

There are three main pairs of salivary glands: the parotid, the submandibular (or submaxillary), and the sublingual glands. There are also many small glands in the tongue, cheeks, lips, and palate, all of which consist entirely of mucous secreting cells (see Histology below) except for the serous glands of von Ebner, which reside within the moats surrounding the circumvallate papillae in the posterior one-third of the tongue, anterior to the terminal sulcus.

Salivary glands are innervated by the parasympathetic and sympathetic branches of the autonomic nervous system.

1 Location
2 Summary
3 Histology
- 3.1 Classification
- 3.2 Structure
4 Innervation
5 Role in disease
6 Diagnostic investigation
7 References
8 External links

[edit] Location

There are three salivary glands:

The parotid gland is located near the ear (par, "next to"; otid, "ear"), and is the largest of the salivary glands.
The sublingual gland lies underneath the tongue.
The submandibular gland is a U-shaped structure, and lies beneath the ramus of the mandible (the angle of the chin).

[edit] Summary

A summary of secretion type, contribution to total salivary volume, and associated cranial nerve is provided in the following table.

Summary of salivary gland features<ref>Douglas F. Paulsen (2000). *Histology & cell biology: examination and board review*. New York: Lange Medical Books, McGraw-Hill. ISBN 0-8385-0593-7.</ref>
Salivary gland	Secretion	Cranial nerve	Parasympathetic ganglion	Contribution to salivary volume
Parotid gland	Serous	CN IX (glossopharyngeal nerve)	Otic	25%
Sublingual gland	Mixed, mostly mucous	CN VII (facial nerve)	Submandibular	5%
Submandibular gland	Mixed, mostly serous	CN VII (facial nerve)	Submandibular	70%

[edit] Histology

Two types of epithelial cells in salivary glands produce either mucous or serous secretions. The parotid gland produces serous secretions. The submandibular and sublingual glands contain a mixture of both types of cells, and produce a mixture of the two liquids.

[edit] Classification

The salivary glands can be classified according to the type of acini that predominates in the gland. Acini are the glandular units of salivary glands, and are called either serous or mucous depending on their secretory product.

The parotid gland is nearly completely composed of serous acini, hence it is considered a serous gland. Sublingual and submandibular glands constitute mixed glands containing both serous and mucous acini. The sublingual glands contain mostly mucous acini and produce mixed, although predominantly mucous secretions. In contrast, the submandibular glands contain mostly serous acini with numerous serous demilunes and consequently secrete a mixed, although mostly serous secretion.

[edit] Structure

The glands are enclosed in a capsule of connective tissue and internally divided into lobules. Blood vessels and nerves enter the glands at the hilum and gradually branch out into the lobules. There are 3 main types of cells that are found in the major salivary glands:

Serous cells, which are pyramidal in shape and are joined to usually form a spherical mass of cells called acinus, with a small lumen in the centre.
Mucous cells are usually cuboid in shape and organised as tubules, consisting of cylindrical arrays of secretory cells surrounding a lumen. These cells produce glycoproteins that are used for the moistening and lubricating functions of saliva.
Myoepithelial cells surround each secretory portion and are able to contract to accelerate secretion of the saliva.

In the duct system, the lumens formed by the secretory cells empty into 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 excretory ducts). The main duct of the salivary glands ultimately empties into the mouth.

[edit] Innervation

Salivary glands are innervated, either directly or indirectly, by the parasympathetic and sympathetic arms of the autonomic nervous system.

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.

The sympathetic nervous system affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands.

[edit] Role in disease

See mumps (parotiditis epidemica) and Sjögren syndrome.

Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland.

Tumors of the salivary glands may occur. These are usually benign, but may be malignant. The most common type of benign tumor is pleomorphic adenoma, followed by Warthin's tumor. The most common malignant tumor is mucoepidermoid carcinoma.