Pituitary gland or Hypophysis

The pituitary gland, or hypophysis (from a Greek root meaning 'to grow under'), is an ovoid gland about a centimetre across and half a gram in weight. It sits in the sella turcica, a bony saddle-shaped cavity of the sphenoid bone at the base of the brain, and is connected to the hypothalamus above it by a thin stalk called the infundibulum. Despite being called the 'master gland' because it controls most of the other endocrine glands, the pituitary is itself entirely governed by signals arriving from the hypothalamus.

The gland is built from two embryologically and functionally distinct lobes. The adenohypophysis (anterior lobe) is true glandular tissue that develops from an embryonic invagination of the pharyngeal epithelium called Rathke's pouch; anatomically it has three regions — the pars distalis, pars intermedia and pars tuberalis. The neurohypophysis (posterior lobe, also called the pars nervosa) is not glandular at all — it develops as a downgrowth of the hypothalamus itself and simply stores and releases hormones made in the hypothalamus.

The anterior lobe secretes six tropic hormones. Growth hormone (GH / somatotropin) promotes growth of essentially all body tissues, boosts protein synthesis, stimulates cartilage and bone formation (chondrogenesis and osteogenesis), helps retain minerals like nitrogen, potassium, phosphorus and sodium, and shifts the body's fuel use toward fat so that glucose is conserved for glucose-dependent tissues like the brain. Thyroid stimulating hormone (TSH) drives the thyroid gland to secrete T3 and T4, and is itself switched on by hypothalamic TRH and switched off by a negative-feedback signal from rising thyroxine. Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to release glucocorticoids and mineralocorticoids, and also promotes melanin synthesis, fatty-acid release from fat stores, and insulin secretion, all under negative-feedback control. Follicle stimulating hormone (FSH) acts, in males, on the germinal epithelium of the seminiferous tubules (with androgens) to drive sperm production, and in females, on the ovary to mature Graafian follicles. Luteinizing hormone (LH), also called interstitial cell stimulating hormone (ICSH) in males, triggers testosterone production from the testicular interstitial (Leydig) cells; in females it works with FSH to mature follicles, independently triggers ovulation, and maintains the corpus luteum. FSH and LH together are called the gonadotropins, and neither is secreted in any real amount until the approach of puberty. Luteotropic hormone (LTH), better known as prolactin, stimulates milk secretion after childbirth; high prolactin during lactation also suppresses LH and ovulation. In non-mammalian vertebrates the pars intermedia additionally secretes melanocyte stimulating hormone (MSH), which darkens skin pigmentation, though this role is negligible in mammals. …