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Physiology · Endocrine

The hypothalamic–pituitary system: overview !

  • Concept
  • Exam priority: high

The hypothalamus gives orders to the pituitary, and the pituitary drives the thyroid, adrenals, gonads, liver and breast.

Updated 2026-11-01

Also called: Hypophyseal portal system, Anterior and posterior pituitary

See it in 3D: Hypothalamus · Pituitary gland · Sella turcica

What it is

The hypothalamus turns signals from the brain and the blood into releasing or inhibiting hormones. These travel through a short portal system to the anterior pituitary, which answers with six trophic hormones. The posterior pituitary is nerve tissue: it stores and releases ADH and oxytocin made in the hypothalamus. Almost every axis is braked by negative feedback from its final hormone.

How it works, step by step

  1. Neurons of the paraventricular, arcuate and other nuclei release hypothalamic hormones into the median eminence.
  2. The primary capillary plexus picks them up and the long portal veins carry them, undiluted, to the anterior pituitary.
  3. Each hypothalamic hormone acts on its own cell type: TRH on thyrotrophs, CRH on corticotrophs, GnRH on gonadotrophs, GHRH on somatotrophs.
  4. The trophic hormone stimulates its target gland, which grows and secretes its final hormone.
  5. The final hormone brakes hypothalamus and pituitary (long loop); the trophic hormone can also brake the hypothalamus (short loop).

Hormone axes and feedback

Hormone axes and feedback: Hypothalamic–pituitary–thyroid axis Cold (mainly in infants) · circadian rhythm−−+++HypothalamusTRHAnterior pituitary (thyrotrophs)TSHThyroid (follicular cells)T4T3Tissues (deiodinases)T4 → T3

Hypothalamic–pituitary–thyroid axisLesion None (normal)

Tap a box to see the hormone, or choose a lesion to see the lab pattern.

  • Stimulates (+)
  • Inhibits / negative feedback (−)
  • Level ↑
  • Level ↓
Illustrative schematic drawn by Durgical: simplified axes and classic lab patterns; not for clinical decisions.

Hormone axes and feedback

Hormone axes and feedback: Hypothalamic–pituitary–adrenal axis Stress · circadian rhythm (peak on waking)−−−+++HypothalamusCRHADHAnterior pituitary (corticotrophs)ACTHAdrenal cortex (fasciculata)CortisolTarget tissues↑ glucose · ↓ inflammation

Hypothalamic–pituitary–adrenal axisLesion None (normal)

Tap a box to see the hormone, or choose a lesion to see the lab pattern.

  • Stimulates (+)
  • Inhibits / negative feedback (−)
  • Level ↑
  • Level ↓
Illustrative schematic drawn by Durgical: simplified axes and classic lab patterns; not for clinical decisions.

Anterior pituitary hormones

HormoneHypothalamic controlTargetMain action
TSHTRH (+)ThyroidT4/T3 synthesis and release; gland growth
ACTHCRH (+), ADH (+)Adrenal cortexCortisol and adrenal androgens
LH and FSHPulsatile GnRH (+)GonadsSex steroids and gametogenesis
GHGHRH (+), somatostatin (−)Liver and tissuesIGF-1, growth, anti-insulin effect
ProlactinDopamine (−), TRH (+)BreastMilk production; suppresses GnRH

Clinical notes

  • Pituitary adenoma: it may oversecrete (prolactinoma, acromegaly, Cushing disease) or compress (headache, bitemporal hemianopia, hypopituitarism).
  • Stalk effect: a non-secreting mass that compresses the stalk raises prolactin a little by cutting off dopamine.
  • Sheehan syndrome: pituitary necrosis after postpartum hemorrhage; failure to lactate is often the first sign.

Test yourself

Think of the answer, then tap the question to see it.

Why does cutting the pituitary stalk raise prolactin while the other anterior pituitary hormones fall?

Prolactin is under tonic inhibition by hypothalamic dopamine. Cutting the stalk removes dopamine (prolactin rises) and also removes TRH, CRH, GnRH and GHRH (the others fall).

Which visual field defect does a macroadenoma with suprasellar extension cause, and why?

Bitemporal hemianopia: the tumor presses on the chiasm from below and damages the crossing nasal fibers, which carry the temporal visual fields.

Why do hypothalamic hormones work at such low concentrations on the anterior pituitary?

They arrive through a direct portal system: from median-eminence capillaries straight to pituitary capillaries, without dilution in the whole blood volume.

What do TSH, LH, FSH and hCG have in common, and what follows from it?

They share the α subunit; the β subunit gives specificity. So very high hCG (molar pregnancy or first trimester) can stimulate the TSH receptor.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

In Biochemistry

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Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 17.3 The Pituitary Gland and Hypothalamus (OpenStax (Rice University), 2022); Anatomy, Head and Neck, Pituitary Gland (StatPearls (NCBI Bookshelf), 2024); Pituitary Adenoma (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 76). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.