SALIVARY GLAND

The 'salivary glands' in mammals are exocrine glands that produce saliva. In other taxa such as insects, salivary glands are often used to produce biologically important proteins such as silk or glues. Salivary glands have proven to be very useful to students of genetics due to the occurrence of polytene chromosomes that are common in the salivary gland cells of many Diptera.

Contents

Function

Summary

Histology

Cells

Ducts

Innervation

Role in disease

Diagnostic investigation

Additional images

References

External links

Function

Saliva 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.
Saliva also has elements that help to neutralise the acid responsible for tooth decay; this is called buffer action (antacid).
The antibacterial properties within saliva help to sustain a neutral balance and prevent the development of germs.

Summary

A summary is provided in the following table.

Summary of salivary gland features^[1]

Salivary gland	Location	Secretion	Cranial nerve	Parasympathetic ganglion	Contribution to salivary volume
Parotid gland	near the ear	Serous	CN IX (glossopharyngeal nerve)	Otic	25%
Sublingual gland	underneath the tongue	Mixed, mostly mucous	CN VII (facial nerve)	Submandibular	5%
Submandibular gland	ramus of the mandible	Mixed, mostly serous	CN VII (facial nerve)	Submandibular	70%
Ebner's glands	surrounding circumvallate papillae	Serous	-	-	-
minor glands	tongue, cheeks, lips, and palate	Mucous	-	-	-

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

Histology

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.

Cells

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. Serous demilunes are found in the submandibular gland.
# 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.

Ducts

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.

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.

★ 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 ß-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. Physiology, 3rd ed., , L., Costanzo, Saunders Elsevier, , The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the blood vessels that supply the glands.it is used to

Role in disease

:''See mumps (parotiditis epidemica), Sjögren's syndrome and Mucocele.''
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.

Diagnostic investigation

A sialogram is a radiocontrast study of a salivary duct.

Additional images

References

1. Histology & cell biology: examination and board review, Douglas F. Paulsen, , , Lange Medical Books, McGraw-Hill, 2000, ISBN 0-8385-0593-7

External links

★ Salivary Gland Disorders at intelihealth.com

★ Illustration at merck.com

★ Illustration at .washington.edu

★ Photo at mgccc.cc.ms.us

★ - "Parotid Tumors, Benign"