The pituitary gland is critically important for regulating growth, reproduction and the maintenance of homeostatic mechanisms. Much of this control comes from the anterior pituitary gland, which secretes polypeptide hormones from five specialized cell types. Disruption of the synthesis and secretion of one or more of these hormones can result in hormone deficiency diseases. Complex control of anterior pituitary function involves hypothalamic, intrapituitary and peripheral signals. Pituitary cell integration of these three tiers of control results in coordinated regulation of differentiated pituitary hormone synthesis and secretion, as well as selective regulation of pituitary cell proliferation. Rhythmic synchronization of the body occurs indirectly through behavioural rest–activity cycles but also in a direct manner through a complex and incompletely understood interplay between hormones and local autonomic innervations. The key hormones implicated in this process — glucocorticoids and catecholamines (specifically, adrenaline and noradrenaline) — are released by the adrenal gland via the hypothalamic–pituitary–adrenal axis (HPA axis).