The Pituitary Gland is located in a bony cavity called Sella turcica and is attached to the hypothalamus by a hypophyseal or infundibular stalk in front of the pons. It consists of three lobes: Anterior lobe, Intermediate, and Posterior Lobe. These three lobes produce nine different types of pituitary hormones.
It is called pars distalis or adenohypophysis. It consists of 5 types of cells which differ in shape, size, staining properties and kind of cytoplasmic granules. The anterior lobe produces and stores six pituitary hormones. Some of these hormones affect the body parts directly, whereas another affect other endocrine glands.
Follicle-Stimulating Hormone (FSH)
It stimulates spermatogenesis in the male and growth of ovarian follicles in the female.
Luteinising Hormone (LH)
In males, it induces the interstitial cells of the testis to produce male sex hormones named androgens such as testosterone. In females, LH induces ovulation of fully mature follicles (Graafian follicles) and cause secretion of female sex hormone, estrogen, from the maturing ovarian follicle and the progesterone, from the corpus luteum. It also maintains the corpus luteum, formed from the remnants of the Graafian follicles after ovulation.
Follicle stimulating hormone (FSH) and Luteinising Hormone (LH) are together referred to as Gonadotrophic hormones (GTHs) or gonadotrophins as they stimulate gonadal activity.
Thyroid Stimulating Hormone (TSH) or Thyrotrophic Hormone or Thyrotrophin
It stimulates the growth of thyroid and the production of thyroid hormones.
Adrenocorticotrophic Hormone (ACTH) or Adrenocorticotrophin
ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids and mineralocorticoids from the adrenal cortex.
Somatotrophic or Growth Hormone (STH or GH) or Somatotrophin
Growth hormone stimulates growth and development of all tissues by accelerating protein synthesis and cell division and by retaining calcium in the body. Over-secretion of GH stimulates the abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting pituitary dwarfism.
Both of these disorders occur due to abnormal secretion during the early age, But if there is an excess of growth hormone after adolescence. The bones of the lower jaw and limbs become abnormally large but the body does not attain a giant stature.
Prolactin Hormone or Leuteotrohic Hormone (LTH)
Prolactin regulates the growth of the mammary glands and formation of milk in them. However, in males and in women (who are not breastfeeding), a prolactin inhibiting hormone produced in the hypothalamus suppresses prolactin synthesis in the anterior pituitary (Adenohypophysis).
It is also called as pars intermedia. In Humans, the pars intermedia is almost merged with pars distalis (anterior pituitary). Intermediate lobe secretes a hormone named melanocyte-stimulating hormone (MSH).
The MSH acts on the melanocytes (melanin-containing cells) and stimulating the synthesis of the black pigment melanin in the skin. It also regulates pigmentation of the skin.
Posterior lobe is composed of non-myelinated nerve fibers and branching nerve cells having brownish granules in their cytoplasm. It is also known as pars nervosa or neurohypophysis. It stores and releases two pituitary hormones called oxytocin and vasopressin. These hormones are actually synthesized by neurosecretory cells in the hypophysis.
Oxytocin acts on the smooth muscles of our body and stimulates their contraction. In females, it stimulates a vigorous contraction of the uterus at the time of childbirth and milk ejection from the mammary gland. Because of its role, oxytocin is called “Birth Hormone” and “Milk Ejecting Hormone”.
Synthetic oxytocin is often given to induce labor or to accelerate labor contractions in a women becoming exhausted during delivery.
Vasopressin acts mainly on the kidney and stimulates resorption of water and electrolytes by the distal tubules and thereby reduce the loss of water through urine (diuresis). Hence, it is also called Anti-Diuretic Hormone (ADH).
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