Pituitary Gland (hypophysis)

Pituitary Gland (hypophysis)

Location : It is a small, red grey pea shaped gland located in a depression called sella turcica of sphenoid bone of cranium. It is attached to hypothalamus by a stalk called pituitary stalk or infundibulum or infundibular stem.

Size : In man it normally measures about 1.3 cm in diameter and weighs about 0.5 gms. It is slightly larger in women, during pregnancy size of pituitary increases slightly. Pituitary is smallest endocrine gland.

Structure : On the basis of anatomy and embryology, pituitary can be divided into two parts adenohypophysis (anterior pituitary) and neurohypophysis (posterior pituitary). Adenohypophysis is an upgrowth of

glandular epithelium from pharynx (primitive gut or Rathke’s pouch) so adenohypophysis is a derivative of buccal ectoderm and neurohypophysis develops as a downward evagination of the neural tube at the base of hypothalamus and therefore represents a true extension of brain. Neurohypophysis is a derivative of neural ectoderm.

Pituitary regulates activities, and directs other glands so it has been nicknamed as the “master endocrine gland” or “Bandmaster of endocrine orchestra”. Recent research has proved that pituitary itself is regulated by hypothalamus so now it is not called master endocrine gland.

Actually hypothalamus should be called as Master or supermaster endocrine gland.

Pituitary is also called “Sentinel gland” as it regulates other glands. It is also called conductor of endocrine symphony.

Cell types in pituitary :- Two major types of cells are found in equal number in the anterior lobe. These are chromophils (granular) and chromophobes (agranular)

Chromophils :- There are granular secretory cells and exist in two forms

Acidophils (Eosinophils) :- These account for about 80% of chromophils and are source of prolactin (PRL) and Growth hormone (GH).

Lactotrophs secrete PRL and somatotrphs secrete GH.

Basophils :- Comprise about 20 % of chromophils and are the source of TSH (Thyroid stimulating hormone), ACTH (Adrenocorticotropic hormone), LH (Luteinizing hormone), FSH (Follicle stimulating hormone) and -LPH(lipotrophic hormone).

Thyrotrophs TSH

Corticotrophs ACTH , MSH

Gonadotrophs FSH, LH

Chromophobes These are not precursors of chromophils and are now known to have an active secretory function.

Neurons in anterior lobe are almost exclusively postganglionic sympathetic fibres that innervate blood vessels. Nerve fibers of

neurohypophysial system terminate mostly in the pars nervosa. Interspersed between these neurosecretory fibres are glial cells called pituicytes,

whose function, other than structural support remains unknown.

Term ABC trinity is also used to describe pituitary. A forcell or acidophils, B for cells or basophils and C for chromophobes.

Castration cells (signet ring cells) : These are altered basophilic cells of anterior pituitary that develop following castration ( castration is surgical removal of gonads, generally applied for testes removal) Body of cell is occupied by a large vacuole that displaces nucleus to periphery, giving the cell a resemblance to signet ring. These are actually gonadotrophs. These disappear after adrenalectomy (surgical removal of adrenal).

Surgical removal of pituitary gland is called hypophysectomy.