Parotid gland

The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.

Location
The parotid glands are found overlying the mandibular ramus and anterior and inferior to the external ear. The glands occupy the parotid fascial spaces, an area posterior to the mandibular ramus, anterior and inferior to the ear on each side of the head. Each gland extends irregularly from the zygomatic arch to the angle of the mandible. This gland is effectively palpated (can be felt) bilaterally by starting anterior to each ear, moving to the cheek area and then inferiorly to the angle of the mandible.

Above the parotid gland lies the external auditory meatus and temporomandibular joint. Below, the parotid overlaps the posterior belly of the digastric muscle. Medially lies the styloid process. Posteriorly, the parotid overflows the sternocleidomastoid and anteriorly it overlies the mandible with the overlying masseter.

The parotid gland resembles a three sided pyramid. The apex of the pyramid is directed downwards. the gland has four surfaces: (1) superior (2) superficial (3) anteromedial & (4) posteromedial. The surfaces are separated by three borders: (1) anterior (2) posterior & (3) medial

Structures which pass through the parotid gland:
 * The facial nerve and its branches run through the gland superficial to the retromandibular vein
 * The external carotid artery, which gives off its two terminal branches, the maxillary artery and the superficial temporal artery, inside the gland
 * The retromandibular vein

Vascularization
Branches of the external carotid artery traverse the glandular tissue and supply the parotid gland with oxygenated blood. The main branch to supply the gland is the transverse facial artery, whereas numerous local veins drain the organ. These veins drain into tributaries of external and internal jugular veins.

The maxillary vein and superficial temporal vein meet to form the retromandibular vein within the parotid gland, but are not responsible for draining it.

Lymphatics mainly comprise pre-auricular lymph nodes.

Pathology
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. Other infections such as bacterial infections can cause parotitis as may blockage of the duct, whether from salivary duct calculi or external compression. 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 patient's 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.

Eighty percent of tumors of the parotid gland are benign. The most common of these include pleomorphic adenoma and Warthin's tumor. 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.

Twenty percent of parotid tumors are malignant with the most common tumors being mucoepidermoid carcinoma and adenoid cystic carcinoma. Critically, the relationship of the tumor to the branches of the facial nerve (CN VII) must be defined because resection may damage the nerves, resulting in paralysis of the muscles of facial expression. If the tumor is deep within the gland, the patient should give consent with specific regard to potential damage of the facial nerve.

Secretion
The parotid gland secretes alpha-amylase which is the first step in the decomposition of starches during mastication. It breaks down amylose (straight chain starch) and amylopectin (branched starch) by hydrolyzing alpha 1,4 bonds.

Additional images
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