The salivary glands in mammals are exocrine glands that produce saliva. They also secrete a chemical (enzymes) that breaks down starch into glucose. 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
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. 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.
In the duct system, the lumens 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 excretory ducts).
The main duct of the salivary glands ultimately empties into the mouth.
Salivary glands release saliva that dilutes the acid found in the stomach.
The parotid glands
are a pair of glands located in the subcutaneous tissues
of the face overlying the mandibular ramus
and anterior and inferior to the external ear
. The secretion produced by the parotid glands is serous
in nature, and enters the oral cavity
through the Stensen's duct
after passing through the intercalated ducts
which are prominent in the gland. Despite being the largest pair of glands, only approximately 25% of saliva is produced by the glands.
The submandibular glands
are a pair of glands located beneath the floor of the mouth, superior to the digastric muscles
. The secretion produced is a mixture of both serous
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
The sublingual glands
are a pair of glands located beneath the floor of the mouth anterior to the submandibular glands
. The secretion produced is mainly mucous
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
There are over 600 minor salivary glands located throughout the oral cavity
within the lamina propria
of the oral mucosa
. 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 usually associated with minor salivary glands.
Von Ebner's Glands
Von Ebner's glands
are glands found in circumvallate papillae
of the tongue. They secrete a serous fluid that begin lipid hydrolysis. They are an essential component of taste
Salivary glands are innervated, either directly or indirectly, by the parasympathetic
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 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. 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, Mucocele, and Salivary gland neoplasm.
Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland.
Tumors of the salivary glands may occur.
is a radiocontrast
study of a salivary duct