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The anterior pituitary is the glandular part of the pituitary gland, containing biological cells that synthesize and release hormones. Signals from the hypothalamus reach it through the hypophyseal portal system: blood passes through one network of capillaries, carries releasing or inhibiting hormones down connecting blood vessels, and enters a second network beside the hormone-secreting biological cells. This provides a direct chemical route for control by the brain.^[ref]

Its products include growth hormone, prolactin and thyroid-stimulating hormone. For example, prolactin promotes milk production, whereas oxytocin released by the posterior pituitary promotes milk ejection. Making milk and moving it outward are distinct controlled processes. Similarly, thyroid-stimulating hormone stimulates release of thyroid hormones, which participate in negative feedback on the control pathway. The anterior pituitary therefore both produces hormones and relays upstream signals; it is not simply a storage site for hormones made in the hypothalamus.^[ref]

A mammary gland is a glandular system that produces milk and carries it through ducts toward the nipple. Secretory epithelial units make the milk, while surrounding contractile cells help expel it into the duct system. The glandular tissue is part of the breast, alongside fat and supporting connective tissue.

Milk production and milk ejection are different processes. Prolactin promotes milk production, whereas oxytocin promotes contraction associated with milk movement or let-down.^[ref] The distinction gives a useful physiological example: material can already have been synthesized yet still require a separate transport mechanism to reach its outlet. Gland size, secretion rate and release of stored secretion are therefore different observations.

Oxytocin is a nine-amino acid peptide hormone synthesized by neurons in the hypothalamus and released into the circulation from the posterior pituitary. It promotes contraction of uterine smooth muscle during childbirth and contraction of cells around mammary secretory units, ejecting milk. Milk ejection is distinct from producing the milk.^[ref]

Childbirth illustrates positive feedback: stretching of the cervix stimulates a neural pathway that increases oxytocin release; stronger uterine contractions can increase the stretch until delivery removes the initiating stimulus. During suckling, sensory input similarly couples an external event to hormone release and milk ejection. These circuits connect sensory neurons, endocrine signaling and mechanical action.^[ref]

The pituitary gland is an endocrine gland at the base of the brain, connected to the hypothalamus. Its anterior pituitary contains hormone-secreting glandular cells; its posterior pituitary contains the terminals of hypothalamic neurons. The two regions consequently communicate with the hypothalamus in different ways.^[ref]

For example, the anterior pituitary secretes prolactin, which promotes milk production, while the posterior pituitary releases oxytocin, which promotes milk ejection. One organ thus participates in distinct, coordinated stages of a physiological response.^[ref]

The posterior pituitary is the neural part of the pituitary gland. Peptide hormones made in the soma of hypothalamic neurons travel down their axons and are released from terminals into the blood. The location of release is therefore different from the location of synthesis.^[ref]

Its released hormones include oxytocin and vasopressin. The latter helps the kidneys conserve water. This is an example of a neuron producing an endocrine output: an electrical signal at its terminal can cause a chemical signal to enter the circulation.^[ref]