pituitary gland

pituitary gland
a small, somewhat cherry-shaped double structure attached by a stalk to the base of the brain and constituting the master endocrine gland affecting all hormonal functions in the body, consisting of an anterior region (anterior pituitary or adenohypophysis) that develops embryonically from the roof of the mouth and that secretes growth hormone, LH, FSH, ACTH, TSH, and MSH, a posterior region (posterior pituitary or neurohypophysis) that develops from the back of the forebrain and that secretes the hormones vasopressin and oxytocin, and an intermediate part (pars intermedia), derived from the anterior region but joined to the posterior region, that secretes the hormone MSH in lower vertebrates. Also called hypophysis. See diag. under brain.

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Endocrine gland lying on the underside of the brain.

It plays a major part in regulating the endocrine system. Its anterior lobe secretes most of the pituitary hormones, which stimulate growth (see growth hormone); egg and sperm development; milk secretion; release of other hormones by the thyroid gland, adrenal glands, and reproductive system; and pigment production. The posterior lobe stores and releases hormones from the hypothalamus that control pituitary function, uterine contraction and milk release, and blood pressure and fluid balance.

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also called  hypophysis 

      ductless gland of the endocrine system (endocrine system, human) that secretes hormones directly into the bloodstream. The term hypophysis (from the Greek, “lying under”) refers to the gland's position on the underside of the brain. The pituitary has a major role in the regulation of many endocrine functions.

      The pituitary gland is divided into two lobes: the anterior lobe, or adenohypophysis, which is derived from an upward outpouching of the roof of the mouth (Rathke's pouch), and the posterior lobe, or neurohypophysis, which is derived from tissue. There are six anterior pituitary hormones, produced by five separate types of cells, and two posterior pituitary hormones.

      The anterior pituitary hormones are corticotropin (adrenocorticotropic hormone) (adrenocorticotropin, or ACTH); follicle-stimulating hormone (FSH) and luteinizing hormone (LH), together known as gonadotropins (and produced by the same cells in the gland); growth hormone (or somatotropin); prolactin; and thyrotropin (thyroid-stimulating hormone, or TSH). Corticotropin stimulates the production of cortisol and androgenic hormones (androgen) by the adrenal cortex. Follicle-stimulating hormone stimulates the production of estrogens and the growth of egg cells (oocytes) in the ovaries (ovary) in women and sperm cells in the testes (testis) in men. Luteinizing hormone stimulates the production of estrogens and progesterone by the ovaries in women and the production of testosterone by the testes in men. Growth hormone stimulates linear growth in children and helps to maintain bone and other tissues in adults. Prolactin stimulates milk production. Thyrotropin stimulates the production of thyroid hormone.

      The production of the anterior pituitary hormones is regulated in part by hormones produced in the hypothalamus, the region of the brain that lies just above the pituitary gland. In general, hypothalamic hormones stimulate production of pituitary hormones, except for prolactin, which is inhibited. The hypothalamic hormones are secreted into a portal vein that traverses directly from the hypothalamus to the anterior pituitary gland, thereby carrying these hormones directly to the pituitary.

      The posterior lobe is composed of the endings of nerve cells located in specialized regions of the hypothalamus. These nerve cells produce two hormones, oxytocin and vasopressin (antidiuretic hormone), that are carried down the nerves and stored in the nerve endings that compose the posterior pituitary gland. The hormones are released into the circulation in response to nerve signals that originate in the hypothalamus and are transmitted to the posterior pituitary. Oxytocin causes contraction of the uterus and milk secretion in women, and vasopressin increases reabsorption of water from the kidneys and raises blood pressure.

       hypopituitarism refers to deficiencies of anterior and posterior pituitary hormones. The extent of deficiency varies from deficiency of a single hormone to deficiencies of all of them, known as panhypopituitarism. tumours that secrete individual anterior pituitary hormones are recognized (see pituitary tumour), and some of them secrete two anterior pituitary hormones, most often growth hormone and prolactin. Posterior pituitary tumours that secrete excess vasopressin or oxytocin do not occur.

Robert D. Utiger

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Universalium. 2010.

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