The parotid gland is a major salivary gland in humans.
It is a bilateral structure, and the largest of the salivary glands.
It is wrapped around the mandibular ramus, and secretes saliva through the Stensen duct
into the oral cavity, to facilitate mastication and swallowing and to begin the digestion
of starches.
The word 'parotid' literally means around the ear.
Structure The parotid glands are a pair of mainly serous
salivary glands located inferior and anterior to the external acoustic meatus draining their
secretions into the vestibule of oral cavity through Stensen duct or parotid duct.
Each gland lies posterior to the mandibular ramus and anterior to the mastoid process
of temporal bone.
The gland is effectively palpated bilaterally.
Start anterior to each ear, move to the cheek area, and then inferior to the angle of the
mandible.
The gland is roughly wedge shaped when seen superficially and is also wedge shaped when
seen on horizontal sections.
The parotid duct or Stenson duct is a long excretory duct that emerges from the anterior
border of the gland, superfcial to the masseter muscle.
The duct pierces the buccinator muscle, then opening up into the oral cavity on the inner
surface of the cheek, usually opposite the maxillary second molar.
The parotid papilla is a small elevation of tissue that marks the opening of the parotid
duct on the inner surface of the cheek.
Histology
The gland has a capsule of its own of dense connective tissue but is also provided with
a false capsule by investing layer of deep cervical fascia.
The fascia at the imaginary line between the angle of mandible and mastoid process splits
into the superficial lamina and a deep lamina to enclose the gland.
Risorius is a small muscle embedded with this capsules substance.
The gland has short striated ducts and long intercalated ducts.
The intercalated ducts are also numerous and lined with cuboidal epithelial cells and have
lumina larger than those of the acini.
The striated ducts are also numerous and consist of simple columnar epithelium, having striations
that represent the infolded basal cell membranes and mitochondria.
Even though the parotid gland is the largest, provides only 25% of the total salivary volume.
The serous cell predominates in the parotid, making the gland secrete a mainly serous secretory
product.
The parotid gland also secretes salivary alpha-amylase which is the first step in the decomposition
of starches during mastication.
It is the main exocrine gland to secrete this.
It breaks down amylose and amylopectin by hydrolyzing alpha 1,4 bonds.
Additionally, sAA has been suggested to prevent bacterial attachment to oral surfaces and
to enable bacterial clearance from the mouth.
Surfaces and borders The gland has four surfaces superficial or
lateral,superior, anteromedial and posteromedial.
The gland has three borders anterior, medial and posterior.
The Parotid gland has two ends: superior end in the form of small superior surface and
an inferior end.
Relation to other structures (1) Superficial or lateral relations: The
gland is situated deep to the skin.
Superficial fascia, superficial lamina of investing layer of deep cervical fascia and
Great auricular nerve (2) Anteromedial relations: The gland is situated
posterolaterally to the mandibular ramus, masseter and medial pterygoid muscles.
A part of the gland may extend between the ramus and medial pterygoid as the pterygoid
process.
Branches of facial nerve and parotid duct emerge through this surface.
(3) Posteromedial relations: The gland is situated anterolaterally to mastoid process
of temporal bone with its attached Sternocleidomastoid and digastric muscles, styloid process of
temporal bone with its three attached muscles and carotid sheath with its contained neurovasculature
(4) Medial relations: The parotid gland comes into contact with the superior pharyngyeal
constrictor muscle at the medial border where the anteromedial and posteromedial surfaces
meet.
Hence there is a need to examine the fauces in parotitis.
Structures that pass through the gland These are from lateral to medial: Facial nerve
Retromandibular vein External Carotid artery Superficial temporal artery branches of the
great auricular nerve Blood supply
The gland is mainly irrigated by External Carotid artery via the posterior auricular
artery and the transverse facial.
Venous drainage Venous return is to the Retromandibular vein.
Lymphatic drainage The gland is mainly drained into the preauricular
or parotid lymph nodes which ultimately drain to the deep cervical chain.
Innervation Innervation is entirely autonomic.
Postganglionic sympathetic fibers from superior cervical sympathetic ganglion reach the gland
as periarterial nerve plexuses around the external carotid artery and their function
is mainly vasoconstriction.
The cell bodies of the preganglionic sympathetics usually lie in the lateral horns of upper
thoracic spinal segments.
Preganglionic parasympathetic fibers leave the brain stem from inferior salivatory nucleus
in the glossopharyngeal nerve and then through its tympanic and then the lesser petrosal
branch pass into the otic ganglion.
There, they synapse with postganglionic fibers which reach the gland by hitch-hiking via
the auriculotemporal nerve, a branch of the mandibular nerve.
Parotid gland salivation is ultimately caused by the glossopharyngeal nerve.
Development The parotid salivary glands appear early in
the sixth week of prenatal development and are the first major salivary glands formed.
The epithelial buds of these glands are located on the inner part of the cheek, near the labial
commissures of the primitive mouth.
These buds will grow posteriorly toward the otic placodes of the ears and branch to form
solid cords with rounded terminal ends near the developing facial nerve.
Later, at approximately 10 weeks of prenatal development, these cords are canalized and
form ducts, with the largest becoming the parotid duct for the parotid gland.
The rounded terminal ends of the cords form the acini of the glands.
Secretion by the parotid glands via the parotid duct begins at approximately 18 weeks of gestation.
Again, the supporting connective tissue of the gland develops from the surrounding mesenchyme.
Clinical relevance
Parotitis Inflammation of one or both parotid glands
is known as parotitis.
The most common cause of parotitis is mumps.
Widespread vaccination against mumps has markedly reduced the incidence of mumps parotitis.
The pain of mumps is due to the swelling of the gland within its fibrous capsule.
Apart from viral infection, other infections such as bacterial infections can cause parotitis.
These infections may cause blockage of the duct by salivary duct calculi or external
compression.
Parotid gland swellings can also be due to benign lymphoepithelial lesions caused by
Mikulicz disease and Sjögren syndrome.
Swelling of the parotid gland may also indicate the eating disorder bulimia nervosa, creating
the look of a heavy jaw line.
With the inflammation of mumps or obstruction of the ducts, the sAA is deposited in the
blood stream, raising sAA levels.
Fibrous reactions Tuberculosis and syphilis can cause granuloma
formation in the parotid glands.
Salivary stones Salivary stones mainly occur within the main
confluence of the ducts and within the main parotid duct.
The patient usually complains of intense pain when salivating and tends to avoid foods which
produce this symptom.
In addition, the parotid gland may become enlarged upon trying to eat.
The pain can be reproduced in clinic by squirting lemon juice into the mouth.
Surgery depends upon the site of the stone: if within the anterior aspect of the duct
a simple incision into the buccal mucosa with sphinterotomy may allow removal; however,
if situated more posteriorly within the main duct, complete gland excision may be necessary.
Injury The parotid salivary gland can also be pierced
and the facial nerve temporarily traumatized when an inferior alveolar local anesthesia
nerve block is incorrectly administered causing transient facial paralysis.
Neoplasia Eighty to eighty-five percent of tumors of
the parotid gland are benign.
The most common of these include pleomorphic adenoma) and Warthin tumormore in males than
in females.
Their importance is in relation to their anatomical position and tendency to grow over time.
The tumorous growth can also change the consistency of the gland and cause facial pain on the
involved side since the facial nerve travels through the gland.
Fifteen to twenty percent of parotid tumors are malignant with the most common tumors
being mucoepidermoid carcinoma and adenoid cystic carcinoma.
Other malignant tumours of the parotid gland include actinic cell carcinoma, carcinoma
ex-pleomorphic adenoma, adenocarcinoma, squamous cell carcinoma and undifferentiated carcinoma.
Critically, the relationship of the tumor to the branches of the facial nerve must be
defined because resection may damage the nerves, resulting in paralysis of the muscles of facial
expression.
Surgical treatment of parotid gland tumors is sometimes difficult because of the anatomical
relations of the facial nerve parotid lodge, as well as the increased potential for postoperative
relapse.
Thus, detection of early stages of a parotid tumor is extremely important in terms of postoperative
prognosis.
Operative technique is laborious, because of relapses and incomplete previous treatment
made in other border specialties.
Additional images
See also This article uses anatomical terminology;
for an overview, see anatomical terminology.
Parotid duct Parotitis
Sjögren syndrome John Leonora
Juxtaoral organ of Chievitz References
External links Illustration at yoursurgery.com
lesson4 at The Anatomy Lesson by Wesley Norman Parotid+gland at eMedicine Dictionary
Salivary gland infections from Medline Plus Salivary gland cancer from American Cancer
Society