Coupon Accepted Successfully!




Thyroid gland is the largest endocrine gland situated in front and sides of lower part of neck opposite Cs- T 4 vertebrae. The weight of thyroid gland is approximately 25 gm. The gland is made of:-

  1. Right and left lobes
  2. Isthmus
  3. Pyramidal lobe


Location and Extent:

The gland lies against vertebrae C5 to T1. Each lobe extends from the middle of thyroid cartilage to the 4th or 5th tracheal ring. The isthmus lies against the 2nd and 3rd tracheal rings.


Capsules of the thyroid:

  1. True capsule - peripheral condensation of the connective tissue of the gland
  2. False capsule - derived from the pretracheal layer of the deep cervical fascia. It also forms the suspensory ligament of Berry which connects the lobe to the cricoid cartilage.

Arterial supply of the thyroid:

  1. Superior thyroid artery - Branch of external carotid artery
  2. Inferior thyroid artery - Branch of Thyrocervical trunk
  3. Thyroidea ima artery - From the brachiocephalic trunk or arch of aorta
    1. Inferior thyroid artery also supplies the parathyroid glands.
    2. The terminal part of the inferior thyroid artery is related to the recurrent laryngeal nerve.
    3. The superior thyroid artery is closely related to the external laryngeal nerve.
    4. During thyroidectomy, superior thyroid artery is ligated near the gland to save external laryngeal nerve, whereas inferior thyroid artery is ligated away from the gland to save recurrent laryngeal nerve.

Venous drainage of the thyroid:

  1. Superior thyroid vein - Drains into Internal jugular vein
  2. Middle thyroid vein - Drains into internal jugular vein
  3. Inferior thyroid vein - Drains into Left brachiocephalic vein
  4. Fourth thyroid vein of Kocher - Drains into internal jugular vein.

Parathyroid Glands

  1. Parathyroid gland, 4 in number (a superior pair and an inferior pair) are located on the posterior border of thyroid gland. The superior parathyroid are also referred to as 'parathyroid IV' because they develop from the fourth pharyngeal pouch, and inferior parathyroid are also referred to as 'parathyroid III' because they develop from the third pharyngeal pouch. Each parathyroid is oval or lentiform in shape, measuring 6 4 2 mm, and each weighs about 50 mg.
  2. Superior parathyroids are more consistent in position lying at the middle of posterior border of thyroid gland immediately above the termination of inferior thyroid artery (80%). In about 20% cases they lie posterolateral to upper pole of thyroid lobe. Inferior parathyroids are more variable in position.ltmay lie; (i) within thyroid capsule, below inferior thyroid artery, (ii) outside thyroid capsule, above inferior thyroid artery, or (iii) within the substance of the lobe near posterior border.
  3. Each parathyroid receives blood supply from inferior thyroid artery, and also from the anastomosis between superior and inferior thyroid arteries.

Pituitary Gland (Hypophysis Cerebri)


  1. Pituitary gland lies within hypophyseal/pituitary fossa or sella turcicaof sphenoid bone which is roofed by diaphragma sellae. It is suspended from tuber cinerium of hypothalamus by infundibulum (pituitary stalk). It is related anterosuperiorly to optic chiasma, laterally to cavernous sinus and inferiorly to sphenoid air sinusesin the body of sphenoid. Pituitary gland is oval in shape, measures 8 12 mm, and weighs about 500 mg. Pituitary gland has two main subdivisions:- (i) Adenohypophysis (anterior lobe), and (ii) Neurohypophysis (posterior lobe),
  2. Adenohypophysis (anterior lobe) include (i) pars anterior or pars distalis or pars glandularis or anterior lobe proper, (ii) pars intermedia (intermediate lobe); and (iii) tuberallobe (pars tuberalis). It develops from an upward growth (Rathke's pouch from the ectodermal roof of stomodaeum.
  3. Neurohypophysis (posterior lobe) include (i) pars posterior or pars nervosa or neural lobe or posterior lobe proper; (ii) infundibulum (infundibular stem); and (iii) median eminence. It develops from a down growth from the 3rd ventricle' diencephalon (neuroectoderm) called infundibulum.
  4. Anterior lobe contains many hormone secreting cells: chromophils (acidophils, basophils), chromophobes and follicullostellate cells. Posterior pituitary contain neuroglia like pituicytes which do not secrete any hormone.
    The posterior pituitary hormones (ADH and oxytocin) are synthesized in hypothalamus and transported to posterior
     lobe by hypothalamohypophyseal nerve fiber tract and stored in the axon terminals of neurohypophysis in Herring bodies before their release.

Blood supply

Pituitary is supplied by a single inferior hypophyseal artery and several superior hypophyseal arteries. These hypophyseal arteries are branches of internal carotid artery. Venous blood enters the adjacent cavernous and intercavernous sinuses. In addition to these vessels there is a hypothalamo-hypophyseal portal venous system connecting the hypothalamus and neurohypophysis with adenohypophysis.

There are three routes for venous drainage of neurohypophysis:

  1. To adenohypophysis via long and short portal vessels.
  2. Into dural venous sinuses via inferior hypophyseal veins.
  3. To hypothalamus via capillaries passing to median eminence.



Pineal Gland

  1. The pineal gland (epiphysis cerebri) is situated in the midline attached to posterior wall of third ventricle. The cells of pineal gland are called pinealocytes and secrete hormone melatonin which helps in regulating sleep-wake cycle. Photoperiodism influences the activity of pineal gland, darkness stimulating the production of melatonin.
  2. Pineal gland lacks blood brain barrier. Calcareous deposits (brain sand or corpora arenacea accumulate in astrocytes of pineal as age advances.


Salivary Glands

Salivary glands are grouped into major salivary glands and minor salivary glands:-

  1. Major salivary glands: - These glands are located away from oral cavity and secrete their secretions into oral cavity through their ducts. Major salivary glands are parotid gland, submandibular gland and sublingual gland.
  2. Minor salivary glands: - These glands are located in the submucosa of oral cavity and secrete their secretions into oral cavity directly. Minor salivary glands are anterior lingual glands; serous gland of Von Ebner; small lingual glands; and labial, buccal and palatal glands.


Parotid Gland

  1. Parotid gland is the largest salivary gland (weight 25 gm) occupying the parotid bed or retro mandibular space, below external acoustic meatus between mandible (ramus) and sternocleidomastoid. The gland overlaps masseter muscle anteriorly. In 20% of individuals this forwards extension is detached and is known as accessory parotid gland and lies between zygomatic arch (above) and parotid duct (below),Parotid gland resembles a three sided pyramid with an apex; four surfaces (superior/base, superficial, anteromedial and posteromedial); and three borders (anterior, posterior and medial).





Superior (Base)
(concave) surface

  • Cartilaginous part of external acoustic meatus.
  • Posterior aspect oftemporomandibualr joint.
  • Auriculotemporal nerve.
  • Superficial temporal artery & vein

Superficial (lateral)
(largest) Surface

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

Anteromedial surface

  • Posterior border of mandible ramus (grooves the surface).
  • Temporomandibular joint (lateral aspect).
  • Masseter and medial pterygoid.
  • Emerging branches of facial nerve, and parotid duct and maxillary artery.

Posteromedial surface

  • Mastoid process with its attached sternocleidomastoid and posterior belly of digastric muscles
  • Styloid process and its attached muscles (styloglossus, stylohyoid and stylopharyngeusi separate the gland from the carotid sheath and its contents internal carotid artery and internal jugular vein.
  • External carotid artery enters the gland.
  • Facial nerve trunk, its temporofacial and cervicofacial divisions enter the gland between styloid and mastoid processes.
  1. Apex overlaps the posterior belly of digastric and adjoining part of carotid triangle. The cervical branch of facial nerveand two divisions ofretro mandibularvein emerge near the apex.
  2. Following structures emerge from anterior border: (i) parotid duct, (ii) most of terminal branches of facial nerve, and (iii) transverse facial vessels.


  1. Structures within the parotid gland are:-
    1. Arteries: - External carotid artery enters through posteromedial surface and divides into maxillary artery and superficial temporal artery.
    2. Veins:-Retromandibular vein is formed by union of superficial temporal and maxillary veins.
    3. Facial nerve enters the gland through posteromedial surface and divides into two branches: -(i) Temporofacial:-divides into temporal and zygomatic branches, and (ii) Cervicofacial: -divides into buccal, marginal, mandibular and cervical branches.


The investing layer of deep cervical fascia forms capsule of parotid gland. The fascia splits into superficial and deep lamina to enclose the gland. A portion of deep lamina, extending between the styloid process and mandible, is thickened to form stylomandibular ligament which separates the parotid gland from submandibular gland. Stylomandibular ligament is pierced by external carotid artery.


Parotid duct (Stenson's duct)

Parotid duct emerges from anterior border of gland and passes forward over lateral surface of masseterand can be palpated at tense anterior margin of masseter muscle. In its course duct pierces buccal fat pad, buccopharyngeal fascia and buccinator muscle (obliquely) and opens on the mucous membrane of cheek opposite to second upper molar tooth. When intraoral pressure is raised (during blowing) the duct is compressed between the buccinator and mucous membrane, preventing inflation of the duct.


Nerve supply

Innervation of salivary gland is as follows:-

  1. Parasympathetic (secretomotor) :- They reach the gland through auriculotemporal nerve as following route:-
    1. Preganglionic fibers: - Originate in inferior salivary nucleus; pass through glossopharyngeal nerve; its tympanic branch; tympanic plexus, and lesser petrosal nerve.
    2. Relay ganglion: - Otic ganglion.
    3. Postganglionic fibers: - Pass through the auriculotemporal nerve to reach the gland.
  2. Sympathetic (Vasomotor):- Derived from the plexus around middle meningeal artery.
  3. Sensory: - Derived from auriculotemporal nerve, except for parotid fascia and overlying skin which are innervated by great auricular nerve (C2, C3).


Parotid gland is the first salivary gland to appear, in early 6th week. It is ectodermal in origin and develops from the buccal epithelium just lateral to the angle of mouth.



Summandibular Gland

This walnut sized gland lies below the mandible in the anterior part of digastric triangle. It is J-shaped and consists of a large superficial and a small deep parts, separated by mylohyoid muscle and continuous with each other around the posterior border of mylohyoid muscle.

Superficial part

It is situated in the anterior part of digastric triangle. The gland is partially closed in a capsule formed by two layers of deep cervical fascia. It has three surfaces: (i) inferior, (ii) lateral, and (iii) medial.

  1. Inferior surface is covered by skin, platysma, cervical branch of facial nerve, deep fascia, facial vein and submandibular lymph nodes.
  2. Lateral surface is related to submandibular fossa (on mandible), medial pterygoid (insertion) and facial artery.
  3. Medial surface is related to mylohyoid, hyoglossus and styloglossus muscles.

Deep part

It lies on the hyoglossus muscle deep to mylohyoid. It is related above to lingual nerve and submandibular ganglion; and below to hypoglossal nerve.



Submandibular duct (Wharton's duct)

It runs forwards on hyoglossus, between lingual and hypoglossal nerves. At the anterior border of the hyoglossus muscle it is crossed by lingual nerve which loops around it. It opens into the floor of mouth, on the summit of the sublingual papilla at the side of frenulum of tongue.


Nerve supply

  1. Secretomotor supply is same for submandibular and sublingual salivary glands, through the submandibular ganglion( Preganglionic fibers arise from superior salivatory nucleus, and pass successively via sensory root of VII nerve (nervus intermedius) ~ facial nerve ~ chorda tympani nerve ~ lingual nerve ~ submandibular ganglion ~ post ganglion fibers ~ submandibular and lingual glands.
  2. Eighty percent of all salivary gland stones (sialolithiasis) occur in submandibular gland.


Sublingual Gland

  1. Sublingual gland is the smallest of the major salivary glands; almond shaped and lies beneath the mucosa of floor of mouth. About 15 ducts emerge from the gland. Most of themopen directly into the floor of mouth on the summit of sublingual fold, but few of them open into submandibular duct.
  2. Ranula is a large mucocele arising from sublingual gland.
  3. Submandibular and sublingual glands develop from endodermal buds arising from the floor of oral cavity.

Test Your Skills Now!
Take a Quiz now
Reviewer Name