Pituitary gland

Hypophysis cerebri

Also known as: hypophysis, master gland

A pea-sized gland (≈1 cm, ≈0.5–0.6 g) sitting in the sella turcica beneath the hypothalamus; its anterior lobe secretes six tropic hormones and its posterior lobe releases ADH and oxytocin.

Show on body map Brain — Midsagittal Section Hypothalamic–Pituitary Axis

Overview

Size≈12 × 9 × 6 mm

Mass≈0.5–0.6 g (up to ≈1 g in pregnancy)

Anterior : posterior≈75–80 % : ≈20–25 %

The pituitary consists of two developmentally and functionally distinct glands fused together. The anterior pituitary (adenohypophysis), about 75–80 % of the gland, is epithelial tissue derived from Rathke's pouch; it is controlled by blood-borne hypothalamic hormones arriving through the hypophyseal portal system. The posterior pituitary (neurohypophysis) is neural tissue — the axon terminals of hypothalamic neurons — and is controlled by nerve impulses.

The gland sits in the hypophyseal fossa of the sella turcica of the sphenoid, roofed by the diaphragma sellae (a dural fold pierced by the stalk). Its position explains the classic presentations of pituitary tumours: upward growth compresses the optic chiasm (bitemporal hemianopia), lateral growth invades the cavernous sinuses (CN III, IV, V1, V2, VI and the internal carotid artery), and the floor of the fossa is thin bone over the sphenoid sinus, which provides the trans-sphenoidal surgical route.

Location: Hypophyseal fossa of the sella turcica (sphenoid bone), middle cranial fossa, below the hypothalamus and optic chiasm.

Parts & subdivisions

Anterior lobe (adenohypophysis)
Pars distalis, pars tuberalis and the rudimentary pars intermedia; secretes GH, PRL, TSH, ACTH, FSH and LH.
Posterior lobe (neurohypophysis)
Pars nervosa, infundibular stem and median eminence; stores and releases ADH and oxytocin.
Infundibulum (stalk)
Connects the gland to the hypothalamus.
Hypophyseal portal system
Superior hypophyseal arteries → primary capillary plexus in the median eminence → long portal veins down the stalk → secondary capillary plexus (sinusoids) in the anterior lobe. It delivers releasing hormones in concentrations far higher than in systemic blood and is a true portal system (two capillary beds in series).

Anatomy

Innervation: Posterior lobe: axons of the hypothalamo-hypophyseal tract. Anterior lobe: no secretomotor nerves (only vasomotor sympathetic fibres from the carotid plexus).
Arterial supply: Superior hypophyseal arteries (from the internal carotid) supply the median eminence and stalk and give rise to the portal system; inferior hypophyseal arteries (cavernous internal carotid) supply the posterior lobe. The anterior lobe has almost no direct arterial supply — it receives portal blood (plus short portal vessels from the posterior lobe), which makes it vulnerable to ischaemia.
Venous drainage: Hypophyseal veins → cavernous sinuses → superior and inferior petrosal sinuses → internal jugular veins (bilateral inferior petrosal sinus sampling uses this route to localise ACTH-secreting adenomas).
Relations: Superior: diaphragma sellae, optic chiasm, hypothalamus. Inferior: sphenoid body and sphenoid sinus. Lateral: cavernous sinuses with internal carotid arteries and CN III, IV, V1, V2 and VI. Anterior: tuberculum sellae. Posterior: dorsum sellae.
Development: Anterior lobe from Rathke's pouch (oral ectoderm); posterior lobe from the infundibulum (diencephalic neuroectoderm). Remnants of the craniopharyngeal duct give rise to craniopharyngiomas and Rathke cleft cysts.

Function

Translates hypothalamic signals into tropic hormones that control the thyroid, adrenal cortex, gonads, liver (IGF-1) and breast.
Stores and releases ADH (water balance) and oxytocin (labour, milk ejection).

Clinical significance

Pituitary adenoma

Benign tumours (≈10–15 % of intracranial neoplasms); microadenomas <10 mm, macroadenomas ≥10 mm. Present with hormone excess (prolactinoma, acromegaly, Cushing disease), mass effect (headache, bitemporal hemianopia) or hypopituitarism. Pituitary apoplexy — haemorrhage or infarction of an adenoma — causes sudden headache, visual loss, ophthalmoplegia and acute adrenal insufficiency.

Sheehan syndrome

Postpartum pituitary infarction after severe obstetric haemorrhage. The pituitary enlarges in pregnancy (lactotroph hyperplasia) but its portal supply does not, so hypotension infarcts it. First sign is often failure of lactation, then amenorrhoea, hypothyroidism and adrenal insufficiency.

Hypopituitarism

Usually from tumour compression, surgery or radiotherapy; hormones are typically lost in the order GH → LH/FSH → TSH → ACTH, with ACTH deficiency the most dangerous. Treat by replacing target hormones (hydrocortisone before levothyroxine, to avoid precipitating adrenal crisis).

Mnemonics

Anterior pituitary hormones

FLAT PiG — FSH, LH, ACTH, TSH, Prolactin, GH.

Compiled from standard anatomy and physiology references — see the Endocrine System sources. For education only; not medical advice.