The Pituitary Gland

Anatomical Position and Relations

The pituitary gland is a pea-sized, oval structure suspended from the underside of the brain by the pituitary stalk (the infundibulum). It lies within a depression of the sphenoid bone known as the sella turcica (‘Turkish saddle’).

The superior surface of the gland is covered by a dural reflection, the diaphragma sellae, which has a central opening to allow passage of the infundibulum.

Key anatomical relations:

• Anteriorly – sphenoid sinus (the pituitary is accessed surgically via this sinus, in a trans-sphenoidal approach).
• Posteriorly – posterior intercavernous sinus, dorsum sellae (posterior wall of the sella turcica), basilar artery, and pons.
• Superiorly – diaphragma sellae and optic chiasm.
• Inferiorly – sphenoid sinus.
• Laterally – cavernous sinuses.

By TeachMeSeries Ltd (2025)

Fig 2
Anatomical position and relations of the pituitary gland.

Anatomical Structure

The pituitary gland is a dual-structure organ composed of two distinct parts with different embryological origins and functions:

• Anterior pituitary (adenohypophysis)
• Posterior pituitary (neurohypophysis)

Anterior Pituitary

The anterior pituitary develops from an ectodermal outpouching of the roof of the pharynx known as Rathke’s pouch. It consists of glandular epithelium and is responsible for synthesising and secreting multiple hormones.

It has three regions:

• Pars distalis (pars anterior) – the largest and most active portion, responsible for hormone secretion.
• Pars intermedia – a thin epithelial layer separating the anterior and posterior lobes.
• Pars tuberalis – an upward extension surrounding the anterolateral aspect of the infundibulum.

Hormone release from the anterior pituitary is regulated by the hypothalamus, which secretes regulatory hormones into the hypophyseal portal system. This system allows hypothalamic hormones to reach the pituitary at high concentration without dilution in the systemic circulation.

Posterior Lobe

The posterior pituitary consists of neurosecretory tissue and is derived from the embryonic forebrain. Functionally, it is an extension of the hypothalamus.

It stores and releases two hormones produced in the hypothalamus:

• Antidiuretic hormone (ADH) – regulates water balance and plasma osmolarity.
• Oxytocin – involved in uterine contraction during labour and milk ejection during lactation.

These hormones are synthesised in the supraoptic and paraventricular nuclei of the hypothalamus, then transported along axons to the posterior pituitary for storage and release.

By TeachMeSeries Ltd (2025)

Fig 3
The structure of the pituitary gland.

Vasculature

The pituitary gland has a unique and complex vascular supply that facilitates communication between the hypothalamus and pituitary.

Both lobes drain via the anterior and posterior hypophyseal veins, but their arterial supply differs.

Anterior Pituitary

The anterior pituitary receives blood from the superior hypophyseal artery, a branch of the internal carotid artery. This artery first forms a primary capillary plexus around the hypothalamus; blood from this plexus drains into portal veins that deliver it to a secondary capillary plexus in the anterior pituitary.

This hypophyseal portal system enables hypothalamic releasing and inhibiting hormones to directly influence anterior pituitary secretion.

Posterior Pituitary

The posterior pituitary and infundibulum receive blood from multiple arteries, primarily the superior hypophyseal, infundibular, and inferior hypophyseal arteries.

By TeachMeSeries Ltd (2025)

Fig 4
The blood supply to the anterior and posterior lobes of the pituitary gland.