Pituitary hormones
Also known as: hypophyseal hormones
The pituitary hormones are the chemical messengers released by the pituitary gland: growth hormone, prolactin, TSH, ACTH, FSH, and LH from the anterior lobe, plus antidiuretic hormone and oxytocin released from the posterior lobe.
The pituitary sits in the sella turcica and has two functionally distinct lobes. The anterior pituitary is true glandular tissue that synthesizes its own hormones, while the posterior pituitary is neural tissue that stores and releases hormones made in the hypothalamus. Both are governed by the hypothalamus, but through different routes: the anterior lobe by releasing factors delivered through the hypophyseal portal vessels, the posterior lobe by axons descending in the pituitary stalk.
The anterior lobe secretes six hormones. Four are tropic, acting on other endocrine glands: TSH stimulates the thyroid, ACTH stimulates the adrenal cortex to produce cortisol, and FSH and LH drive gametogenesis and gonadal steroid production. Two act directly on tissues: growth hormone, which promotes growth largely through IGF-1 from the liver, and prolactin, which stimulates milk production. Their hypothalamic controls include TRH, CRH, GnRH, and GHRH as stimulators, with somatostatin inhibiting growth hormone and dopamine tonically inhibiting prolactin — which is why interrupting the stalk raises prolactin while lowering the other anterior hormones.
The posterior lobe releases two hormones synthesized in the supraoptic and paraventricular nuclei. Antidiuretic hormone (vasopressin) increases water reabsorption by inserting aquaporin-2 channels in the renal collecting duct and constricts vessels at higher concentrations. Oxytocin causes uterine contraction during labor and milk ejection during nursing, both classic positive feedback loops.
Disorders map cleanly onto these hormones and are tested accordingly: prolactinoma, acromegaly and gigantism from growth hormone excess, Cushing disease from an ACTH-secreting adenoma, SIADH and diabetes insipidus from ADH excess and deficiency, and panhypopituitarism from Sheehan syndrome. USMLE Step 1 covers pituitary hormones in endocrine physiology, expecting you to know each hormone's source lobe, hypothalamic control, target, and the negative feedback loop that regulates it.
Key takeaways
- The anterior pituitary makes GH, prolactin, TSH, ACTH, FSH, and LH; the posterior pituitary releases ADH and oxytocin made in the hypothalamus.
- TSH, ACTH, FSH, and LH are tropic hormones acting on other endocrine glands, while GH and prolactin act directly on tissues.
- Hypothalamic control reaches the anterior lobe through portal vessels and the posterior lobe through axonal transport.
- Dopamine tonically inhibits prolactin, so stalk interruption raises prolactin while other anterior hormones fall.
- ADH promotes renal water reabsorption via aquaporin-2, and oxytocin drives uterine contraction and milk ejection.