Write detailed note on hormones of Neurophyophysis and Adenohypophysis


Hormones of Neurohypophysis:

It does not manufacture any hormones. Instead, neurosecretory cells of hypothalamus synthesize and secrete two hormones, antidivretic hormone and oxytocin, which move down nerve axons into neurohypophysis, where they are stored in the axon terminals until released. Diurectics stimulate urine excretion whereas antidiuretics decrease urine secretion. When a mammal begins to loose water and becomes dehydrated, antidiuretic hormone (A DH or vasopressin) is released in increased water absorption in the kidneys so that less urine is secreted, and water is retained. This negative feedback system thus restores water and solute homeostasis.

Oxytocin stimulates smooth muscle contraction of the uterus to aid in the expulsion of the offspring and promotes the ejection of milk from the mammary glands to provide nourishment for new born.
Both A Dh and oxytocin.

Neurohypophysis is larger in animals that live in arid parts of the world where water conservation is crucial. Also the structure of two hormones is similar except for a difference in two of the amino acids.

Hormones of Adenohypophysis:

It is the true endocrine portion of the pituitary. It synthesizes six different polypeptide hormones. Two are true hormones, hormones whose primary target is another endocrine gland. Two non tropic hormones are growth hormone and prolactin.

Growth hormone (GH) or Somatotropin (STH) directly induces the cell division necessary for growth and protein synthesis in most types of cells by stimulating the uptake of amino acids, RNA synthesis and ribosome activity. Prolactin stimulates reproductive migrations in many mammals such as elk and cribon. It also enhances mammary gland development and milk production in female mammals. It stimulates milk ejection from the mammary glands, but not its production. Thyroptropin (TSH) stimulates the thyroid glands synthesis and secretion of thyroxine.

Adrenocotriotropic hormone (ACTH) stimulates the adrenal gland to produce and secrete steroid hormones called cortisol. Secretion of ACTH is regulated by the secretion of corticotropin releasing factor from the hypothalamus which in turn is regulated by feedback system that involves such factors as stress, insulin, ADH and other hormones.

Adenohypophysis produces two gonadotropins (hormones that stimulate the gonads). Lutenizing hormone (LH) receives its name from corpus luteum, a temporary endocrine tissue in the ovaries that secretes female sex hormones estrogen and progesterone. In the female an increase of LH in the blood stimulates evolution. In the male, the target cells of LH are cells in the testes that secrete male hormone testosterone. In the female follicle stimulating hormone (FSH) stimulates the follicular cells in the ovaries to develop into nature eggs and to produce estrogen. In the male, FSH stimulates the cells of the testes to produce sperm.

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