The pituitary is roughly pea-sized and sits in a bony pocket called the sella turcica at the base of the brain, directly below the hypothalamus. It is called the master gland because its output controls the thyroid, adrenals, gonads, growth, lactation, and water balance. When the pituitary fails, most of the endocrine system fails with it.
At a glance
What it does
Receives commands from the hypothalamus and issues hormonal orders to downstream glands. It is organized into two lobes with completely different embryonic origins and physiologies — they are more like two glands that share an address than a single organ.
The anterior pituitary (adenohypophysis) makes and releases its own hormones in response to releasing hormones carried from the hypothalamus by a specialized portal blood system. The posterior pituitary (neurohypophysis) is actually brain tissue — it stores and releases hormones made in hypothalamic neurons whose axons extend into the gland.
Anterior pituitary hormones
Six classical outputs, each with a specific target:
- TSH (thyroid-stimulating hormone) — tells the thyroid to make T3 and T4. Regulated by TRH from the hypothalamus, suppressed by high thyroid hormone.
- ACTH (adrenocorticotropic hormone) — tells the adrenal cortex to make cortisol. Driven by CRH, suppressed by cortisol. The spine of the HPA axis.
- LH and FSH (the gonadotropins) — tell the testes (Leydig and Sertoli cells) or ovaries (theca and granulosa cells) to make sex hormones and produce gametes. Driven by pulsatile GnRH.
- GH (growth hormone) — drives growth in children, supports lean tissue and metabolism in adults. Secreted in pulses, mostly during slow-wave sleep, driven by GHRH and suppressed by somatostatin.
- Prolactin — drives milk production postpartum; tonically inhibited by dopamine from the hypothalamus, which is why dopamine-blocking drugs cause hyperprolactinemia.
Posterior pituitary hormones
Two hormones made in hypothalamic neurons, stored in the posterior lobe, released into blood on demand:
- ADH / vasopressin — tells kidneys to hold on to water and constricts vessels. Deficiency causes diabetes insipidus (massive dilute urine); excess causes SIADH (water retention, low sodium).
- Oxytocin — drives uterine contraction in labor and milk ejection in breastfeeding, and acts in the brain on social bonding circuits. Not the "love hormone" in the cartoonish way popular media uses it, but it does modulate pair bonding and trust signals.
How the axis works
Most pituitary hormones live inside a three-tier feedback loop: hypothalamus releases a releasing hormone, pituitary releases a stimulating hormone, target gland releases its product, and that product feeds back to suppress the upstream signals. This is why serum lab tests interpret pituitary function indirectly — high TSH with low T4 suggests primary thyroid failure with a pituitary still shouting at it; low TSH with low T4 suggests the pituitary itself is broken.
Pulsatility matters. GnRH comes in pulses every 60-90 minutes; a constant signal actually desensitizes the pituitary (this is why GnRH agonists shut down sex hormone production instead of raising it). ACTH and GH also pulse, with circadian patterns.
When it goes wrong
Pituitary adenomas are common — autopsy data find them in roughly 10-15% of adults, though most are silent. Functional adenomas cause disease by oversecreting one hormone: prolactinomas cause amenorrhea, infertility, and galactorrhea; GH-secreting tumors cause acromegaly in adults or gigantism in children; ACTH-secreting tumors cause Cushing's disease.
Hypopituitarism — the pituitary itself failing — knocks out multiple axes simultaneously. Causes include tumor, surgery, radiation, Sheehan's syndrome (postpartum infarction from massive hemorrhage), traumatic brain injury, and autoimmune hypophysitis. Patients need replacement of whichever hormones are missing, often for life.
Diabetes insipidus (posterior pituitary or hypothalamic damage) causes uncontrollable thirst and urination and is treated with desmopressin.
Interactions
The pituitary integrates stress, sleep, nutrition, and circadian signals before dosing out its hormones. Chronic stress raises cortisol output via CRH/ACTH and blunts gonadotropin pulsing, which is why high-stress seasons drop libido and mess up cycles. Sleep deprivation suppresses GH pulses and disrupts prolactin and cortisol rhythms. Severe caloric restriction suppresses LH/FSH — the "functional hypothalamic amenorrhea" picture common in athletes and dieters.
Honest take
Pituitary dysfunction is systematically under-diagnosed after traumatic brain injury — rates of post-concussion hypopituitarism are substantial in the literature but few clinicians screen for it in the years after. If you had a real head injury and things went downhill (libido, energy, mood, cold intolerance) and never recovered, a targeted pituitary workup is worth the conversation. Separately, "pituitary peptide" products sold online (GHRP-2, ipamorelin, etc.) do measurably bump GH pulses, but the evidence that this produces meaningful benefit in already-healthy adults is thin and the regulatory status is real.
Sources
- Melmed, Pituitary Disorders — the standard reference.
- Fleseriu et al., Lancet Diabetes & Endocrinology (2021) — consensus statements on pituitary tumor management.
- Tanriverdi et al., Endocrine Reviews — pituitary dysfunction after traumatic brain injury.