Pituitary Gland

Anatomy of Pituitary Gland

This post also contains information about function ,development and position about Pituitary Gland

Development:

Develops from 2  sources-
• Ectodermal outpocketing of the stomodeum (Rathke’s pouch)
•Downward extension of diencephalon (infundibulum)

Approax 3 weeks embryo-Rathke’s pouch appears on the roof of the stomodeum

By the end of 2nd month the connections of the pouch with the oral cavity degenerates & disappears

• Anterior wall of Rathke’s pouch proliferates greatly- forms the anterior lobe of hypophysis.

• Posterior wall of the Rathke’s pouch develop into pars intermedia

• Infundibulum gives rise to the stalk and pars nervosa 

• It is composed of neuroglial cells and nerve fibres

• Persistent of Rathke’s pouch in the roof of the pharynx –pharyngeal hypophysis

Craniopharyngiomas-special type of tumor arises from the remnants of Rathke’s pouch

Subdivisions 

Consists of 2 main parts-

– Adenohypophysis (anterior lobe) 

• pars anterior (pars distalis)

• pars intermedia 

• pars tuberalis                                                           

– Neurohypophysis (posterior lobe)

• pars posterior or pars nervosa

• infundibulum and 

• median eminence.

Contents

• Pars anterior: consists of chromophil cells and chromophobe cells
• Chromophil cells classified into – Acidophil cells (somatotrophs, mammotrophs & corticotrops))
– basophil cells (corticotrophs, thyrotrophs, gonadotrophs)
• Chromophobe cells: they contain very few granules in the cytoplasm
• Pars tuberalis: consists of some acidophil and basophil cells
• Pars intermedia: it is poorly developed in human


• Pars posterior: 
– unmyelinated nerve fibres. supporting cells called pituicytes
– Secretes vasopressin (anti-diuretic hormone; ADH) and oxytocin

Arterial supply

Anterior lobe: by superior hypophyseal artery (branch of internal carotid artery)

– Breaks up and form capillary plexus in the median eminence and infundibular stem

– Long and short portal vessels arise from these plexus and supply the anterior lobe 

• Posterior lobe: by inferior hypophyseal artery (branch of internal carotid artery)

– Enters the posterior lobe and form capillary plexus to supply it.Diagram summarizing the vasculature of the hypothalamic median eminence,infundibulum and the rest of the hypophysis cerebri

• Hypothalamo-hypophyseal portal system– Axons of mainly arcuate nucleus reach the median eminence 

and infundibulum forming tubero-infundibular tract which lie in close contact with capillary plexus

– These fibers convey  inhibiting factors which is taken up by blood and reach the anterior lobe

– Thus anterior lobe is connected with hypothalamus via neurovascular portal system

Arcuate nucleus

– Posterior lobe is connected with the paraventricular and supra-optic nuclei of hypothalamus via hypothalamo-hypophyeal tract

– Paraventricular nuclei secrete oxytocin and supra-optic nuclei secrete vasopressin

– These hormones are transported by the hypothalamo-hypophyseal tract to the posterior lobe

Venous Drainage

-Small veins arise from the surface of the gland and drain into neighboring dural sinuses

-Venous blood carries the hormones from gland to the target cells

Functions

Hormones secreted from the pituitary gland help control the following body processes:

• Growth (Excess of HGH can lead to gigantism and acromegaly.)
• Blood pressure
• Some aspects of pregnancy and childbirth including stimulation of uterine contractions during childbirth
• Breast milk production
• Sex organ functions in both males and females
• Thyroid gland function
• The conversion of food into energy (metabolism)
• Water and osmolarity regulation in the body
• Water balance via the control of reabsorption of water by the kidneys
• Temperature regulation
• Pain relief

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