Hypothalamus and Pituitary Gland

The hypothalamus is the link. The hypothalamus sits in the brain and connects the nervous system to the endocrine system. It controls the pituitary gland just below it, and through the pituitary it influences much of the body's hormone activity. The pituitary has two lobes controlled in different ways.

Anterior pituitary — controlled by hormones. The hypothalamus sends releasing and inhibiting hormones through a small blood network to the anterior pituitary, telling it when to secrete its own hormones. Several anterior pituitary hormones are tropic hormones — they control other glands:

• TSH (thyroid-stimulating hormone): stimulates the thyroid.
• ACTH (adrenocorticotropic hormone): stimulates the adrenal cortex (cortisol).
• FSH and LH (gonadotropins): stimulate the gonads (ovaries/testes) for reproduction.
• GH (growth hormone): promotes growth of bone and muscle and affects metabolism.
• Prolactin (PRL): stimulates milk production.

Because TSH, ACTH, and the gonadotropins each drive another gland, the anterior pituitary is a central relay: hypothalamus → pituitary → target gland → hormone, all governed by negative feedback.

Posterior pituitary — controlled by nerves. The posterior pituitary doesn't make hormones itself; it stores and releases two hormones actually produced by the hypothalamus and delivered down nerve fibers:

• ADH (antidiuretic hormone, vasopressin): promotes water reabsorption by the kidneys, reducing urine output and conserving body water (central to fluid balance).
• Oxytocin: stimulates uterine contractions during labor and milk ejection during breastfeeding (a classic positive-feedback hormone).

Why the "master gland" label — with a caveat. The pituitary is called the master gland because it directs the thyroid, adrenals, and gonads. But the hypothalamus directs the pituitary, so the true top of the hierarchy is the hypothalamus — the real bridge between brain and hormones.

How it works

The command chain:

Hypothalamus (releasing/inhibiting hormones)
   → Anterior pituitary → tropic hormones (TSH, ACTH, FSH/LH) → target glands (thyroid, adrenal, gonads)
   → also GH (growth), prolactin (milk)
Hypothalamus (makes ADH, oxytocin) → stored in posterior pituitary → released into blood
Negative feedback from target-gland hormones regulates the whole chain

Comparisons

Common confusions

• Anterior vs posterior pituitary. Anterior makes hormones (controlled by hypothalamic hormones); posterior only stores/releases ADH and oxytocin (made by the hypothalamus).
• Master gland caveat. The pituitary directs other glands, but the hypothalamus directs the pituitary.
• ADH vs oxytocin. ADH = water balance (kidneys); oxytocin = labor and milk ejection.
• Tropic hormones control other glands (TSH, ACTH, FSH/LH); GH and prolactin act more directly on tissues.

Memory aids

• Anterior pituitary hormones: "FLAT PiG" → FSH, LH, ACTH, TSH, Prolactin, GH.
• Posterior stores 2: "ADH + Oxytocin."
• ADH = "Add water back (Anti-Diuretic)."

Quick review

• The hypothalamus controls the pituitary, linking the nervous and endocrine systems.
• The anterior pituitary (controlled by hypothalamic hormones) secretes TSH, ACTH, FSH, LH, GH, prolactin — several are tropic (control other glands).
• The posterior pituitary stores/releases hypothalamic ADH (kidney water reabsorption) and oxytocin (labor, milk ejection).
• Disorders (GH excess/deficiency, diabetes insipidus) and lab reasoning (tropic + target hormone) follow from this hierarchy.