The pituitary gland is located in a bony cavitycalled sella tursica and is attached tohypothalamus by a stalk (Figure 22.2). It isdivided anatomically into an adenohypophysisand a neurohypophysis. Adenohypophysisconsists of two portions, pars distalis and parsintermedia. The pars distalis region of pituitary,commonly called anterior pituitary, producesgrowth hormone (GH), prolactin (PRL), thyroidstimulating hormone (TSH),adrenocorticotrophic hormone (ACTH),luteinizing hormone (LH) and folliclestimulating hormone (FSH). Pars intermediasecretes only one hormone called melanocytestimulating hormone (MSH). However, inhumans, the pars intermedia is almost mergedwith pars distalis. Neurohypophysis (parsnervosa) also known as posterior pituitary, storesand releases two hormones called oxytocin andvasopressin, which are actually synthesised bythe hypothalamus and are transported axonally to neurohypophysis.Over-secretion of GH stimulates abnormal growth of the body leadingto gigantism and low secretion of GH results in stunted growth resultingin pituitary dwarfism. Excess secretion of growth hormone in adultsespecially in middle age can result in severe disfigurement (especially ofthe face) called Acromegaly, which may lead to serious complications,and premature death if unchecked. The disease is hard to diagnose inthe early stages and often goes undetected for many years, until changesin external features become noticeable. Prolactin regulates the growth ofthe mammary glands and formation of milk in them. TSH stimulates thesynthesis and secretion of thyroid hormones from the thyroid gland. ACTHstimulates the synthesis and secretion of steroid hormones calledglucocorticoids from the adrenal cortex. LH and FSH stimulate gonadalactivity and hence are called gonadotrophins. In males, LH stimulatesthe synthesis and secretion of hormones called androgens from testis. Inmales, FSH and androgens regulate spermatogenesis. In females, LHinduces ovulation of fully mature follicles (graafian follicles) and maintainsthe corpus luteum, formed from the remnants of the graafian folliclesPosteriorpituitaryAnteriorpituitaryHypothalamusHypothalamicneuronsPortal circulationFigure 22.2 Diagrammatic representation ofpituitary and its relationship with
after ovulation. FSH stimulates growth anddevelopment of the ovarian follicles in females. MSHacts on the melanocytes (melanin containing cells) andregulates pigmentation of the skin. Oxytocin acts onthe smooth muscles of our body and stimulates theircontraction. In females, it stimulates a vigorouscontraction of uterus at the time of child birth, and milkejection from the mammary gland. Vasopressin actsmainly at the kidney and stimulates resorption of waterand electrolytes by the distal tubules and therebyreduces loss of water through urine (diuresis). Hence,it is also called as anti-diuretic hormone (ADH).An impairment affecting synthesis or release of ADHresults in a diminished ability of the kidney to conservewater leading to water loss and dehydration. Thiscondition is known as Diabetes Insipidus.