Parotid gland
The parotid gland
is the largest of the salivary glands.
The parotid, a
serous compound tubulo-alveolar gland, is yellowish, lobulated, and irregular
in shape.
It occupies the interval between the
sternomastoid muscle and the mandible.
Average Wt - 25gm (varies in weight
from 14 to 28 gm)
Surface anatomy
The parotid gland
lies inferior to the zygomatic arch, anteroinferior to the external acoustic
meatus, anterior to the mastoid process, and posterior to the ramus of the
mandible.
Relations
The parotid gland
is enclosed in a sheath (parotid fascia) and is shaped roughly like an inverted
pyramid, with three (or four) sides (fig A).
It has a base
(from which the superficial temporal vessels and auriculotemporal nerve
emerge),apex (which descends inferior and posterior to the angle of the
mandible),and lateral, anterior, and posterior (or posterior and medial)
surfaces.
The
lateral surface is
superficial and contains lymph nodes.
The
anterior surface is
grooved by the ramus of the mandible and masseter (fig.B), producing a medial
lip (from which the maxillary artery emerges) and a lateral lip, under cover of
which the parotid duct, branches of the facial nerve, and the transverse facial
artery emerge (see fig. C).
The
posterior surface is
grooved by the mastoid process and the
sternomastoid and digastric muscles and more medially by the styloid process and its
attached muscles.
Medially,
the superior part of the gland is pierced by the facial nerve and the inferior
part by the external carotid artery.
The following structures lie partly within the parotid gland, from superficial to deep:
1. The facial
nerve forms the parotid plexus within the gland and separates the glandular
tissue partially into superficial and deep layers ("lobes"). In
surgical excision of the parotid gland (e.g., for a tumor), damage to the
facial nerve is a possibility.
2. The superficial
temporal and maxillary veins unite in the gland to form the retromandibular
vein, which contributes in a variable manner to the formation of the external
jugular vein (see fig. D).
3. The
external carotid artery divides within the parotid gland into the superficial
temporal and maxillary arteries.
Parotid duct
The parotid duct
is about 7 cm long
The parotid duct,
emerging under cover of the lateral surface, runs anteriorward on the masseter
and turns medially to pierce the buccinator.
The branching of the duct can be examined
radiographically after injection of a radio-opaque medium.
The parotid duct,
which is palpable, opens into the oral cavity on the parotid papilla opposite
the upper second molar tooth.
Innervation of parotid
gland ( fig. E)
Preganglionic
parasympathetic secretomotor fibers (from the glossopharyngeal, tympanic, and
lesser petrosal nerves) synapse in the otic ganglion.
Postganglionic fibers travel with the
auriculotemporal nerve and so reach the gland.
Cranial nerves VII and IX communicate, so
that secretory fibers to each of the three major salivary glands may
travel in both the facial and glossopharyngeal nerves.
The
sympathetic supply to the salivary glands includes vasomotor fibers.
Blood supply
The arteries
supplying the parotid gland are derived from the external carotid, and from the
branches given off by that vessel in or near its substance. The veins empty
themselves into the external jugular, through some of its tributaries.
Lymphatics
The lymphatics end
in the superficial and deep cervical lymph glands, passing in their course
through two or three glands, placed on the surface and in the substance of the
parotid.