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PAROTID GLAND

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PAROTID GLAND

PAROTID GLAND       
  • Parotid gland is the largest major salivary gland (weight 25 gm).
  • occupying the parotid bed or retromandibular space, below external acoustic meatus b/w ramus of mandible & sternocleidomastiod.
  • Paired parotid glands overlap masseter muscle anteriorly. 
  • On the surface of the masseter, small detached part lies between  zygomatic arch and parotid duct called as Accessory parotid gland or ‘socia parotidis’ or pars accessaria.
  • Parotid gland resembles a three sided pyramid with an apex, four surfaces (superior/ base, superficial, anteromedial & posteromedial); & three borders (anterior, posterior & medial).
  • Wedge-shaped when viewed externally , with the base above & the apex behind the angle of the mandible.
RELATIONS:                                                                                                        

SURFACE

RELATIONS

SUPERIOR(BASE) (CONCAVE)
  • Cartilagenous part of external acoustic meatus.
  • Posterior aspect of TMJ.
  • Auriculotemporal nerve
  • Superficial temporal artery & vein

SUPERFICIAL (LATERAL)

(LARGEST)
  • Skin
  • Superficial fascia containing anterior branches of great auricular nerve, superficial parotid lymph nodes & posterior border of platysma.
  • Paritid capsule (investing layer of deep cervical fascia)
  • SAMS (superficial muscular aponeurotic system) &
  • Risorius

ANTEROMEDIAL SURFACE
  • Posterior border of mandible ramus (grooves the surface)
  • Temporomandibular joint (lateral aspect)
  • Masseter & medial pterygoid.

POSTEROMEDIAL SURFACE
  • Mastoid process with its attached sternocleidomastoid & posterior belly of digastric muscle.
  • Styloid process & its attached muscles (styloglossus, stylohyoid & stylopharyngeus)
  • External carotid artery enters the gland.
  • Facial nerve trunk, its temporofacial & cervicofacial divisions enter the gland.

  • APEX overlaps the posterior belly of digastric & adjoining part of carotid triangle.
  • The cervical branch of facial nerve & two divisions of retromandibular vein emerge near apex.

Following structures energe from anterior border:

1. Parotid duct

2. Terminal branches of facial nerve

3. Transverse facial vessels

PAROTID CAPSULE:

  • The investing layer of the deep cervical fascia forms capsule of parotid gland.
  • The fascia consists of  :-

1. Superficial layer

2. Deep layer  

  • Stylomandibular ligament separates the parotid glands from submandibular salivary gland.
  • Stylomandibular ligament pierced by external carotid artery.

The attachments of the Parotid fascia include :

1. Anterior – Mandible

2. Inferior – Stylomandibular ligament

3. Posterior –Styloid process

STRUCTURES WITHIN GLAND:

Arteries:

  • External carotid artery enters through posteromedial surface
  • Maxillary artery
  • Superficial temporal vesseL
  • Posterior auricular artery

Veins:

  • The retromandibular veins is formed within the gland by the union of the superficial temporal and maxillary veins.
  • In the lower part of the gland, the vein divides into anterior and posterior divisions which emerge at the apex of the gland.

Facial Nerve:

  • It enters the gland through the upper part of its posteriomedial surface, and divides into its terminal branches within the glands.
  • Branches appear on the  surface at the anterior border.
  • The arrangement of Branches of Facial nerve after exiting from Parotid gland is given the name as Pes Anserinus.
Parotid Duct (Stenson’s duct)
  • Parotid duct emerges from anterior border of gland & passes forward over lateral surface of masseter & can be palpated at tense anterior margin of masseter muscle.

Anterior border of the masseter, it turns medially and pierces:

– Buccal pad of fat.

– Buccalpharyngeal fascia

– Buccinator

  • The duct runs forward for a short distance between the buccinator and the oral mucosa.
  • The duct turns opens into the vestibule of the mouth (gingivo- buccal vestibule) opposite the crown of the upper 2nd molar tooth
NERVE SUPPLY:
  • Parotid gland is pierced but not innervated by facial nerve.

1. PARASYMPATHETIC (SECRETOMOTOR)

  • derived from auriculo temporal nerve as following route:
i) Preganglionic fibers:
  • Originate in inferior salivary nucleus
  • Pass through glossopharyngeal nerve; its tympanic branch; tympanic plexus, & lesser petrosal nerve 
ii) Relay ganglion: Otic ganglion
 
iii) Postganglionic fibers: Pass through the auriculotemporal nerve to reach the gland.
 
2. SYMPTHETIC SUPPLY- vasomotor
  •  Derived from the plexus around the external carotid artery.
3. SENSORY NERVES-
  • From the auriculotemporal nerve, except for parotid fascia & overlying skin which are innervated by Great auricular nerve (C2, C3). 

Exam Important

  • Secretomotor fiber to parotid salivary gland is supplied by otic ganglion.
  • The arrangement of Branches of Facial nerve after exiting from Parotid gland is given the name as Pes Anserinus.
  • Parotid duct pierces buccinator muscle.
  • Parotid gland is pierced but not innervated by facial nerve.
  • The parasympathetic secretomotor fibres to parotid arises from the glossopharyngeal nerve & reaches the gland via tympanic branch, the lesser petrosal nerve, the otic ganglion and the auriculotemporal nerve.
  • Parotid capsule is derived from deep cervical fascia.
  • Postganglionic fibres to parotid gland is supplied by auriculotemporal nerve.
  • Parotid duct is also k/as Stenson’s duct.
  • The duct turns opens into the vestibule of the mouth (gingivo- buccal vestibule) opposite the crown of the upper 2nd molar tooth
  • Parotid duct pierces Buccal pad of fat, Buccalpharyngeal fascia & Buccinator.
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