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Hypothalamus, Pituitary Gland and Pineal Gland

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Hypothalamus, Pituitary Gland and Pineal Gland - Lesson Summary

The three endocrine glands in the brain are the hypothalamus, pituitary and pineal glands.
The hypothalamus contains neuro-secretory cells that produce neurohormones - releasing hormones and inhibiting hormones, which regulate the synthesis and secretion of pituitary hormones. The releasing hormone such as GnRH stimulates the release of FSH and LH from the pituitary. While the inhibiting hormone such as somatostatin inhibits the release of the growth hormone from the pituitary. Hypothalamus maintains homeostasis inside the body and regulates most of its physiological activities.

The pituitary gland is the master of endocrine glands, because it produces hormones that control the thyroid gland, the adrenal cortex and the gonads. The pituitary is divided into the adenohypophysis and the neurohypophysis. It includes pars intermedia and pars distalis. The pars distalis produces GH, PRL, TSH, ACTH, LH and FSH. The pars intermedia secretes MSH.
 
The GH acts on the liver, skeletal muscle, cartilage, bone and causes cells to grow and multiply. Hyposecretion of this hormone during childhood causes dwarfism and hypersecretion causes gigantism; and hypersecretion in adults causes acromegaly. PRL stimulates the development of the mammary glands during pregnancy and lactation after childbirth. TSH stimulates the secretion of T 3 and T 4 by the thyroid gland. ACTH stimulates secretion of glucocorticoids and the sex corticoids by the adrenal cortex. In females, LH stimulates ovulation of the graafian follicles, formation of the corpus luteum and secretion of progesterone by the corpus luteum. Hyposecretion of this hormone leads to sterility in females. In males, LH stimulates the leydig cells in the testes to secrete androgens. FSH, stimulates the development of several ovarian follicles in the ovaries. In males, FSH and androgens stimulate spermatogenesis in the seminiferous tubules.

Together FSH and LH are called gonadotrophins. MSH secreted by the pars intermedia, regulates skin pigmentation by stimulating the melanocytes. The posterior lobe of the pituitary gland is under the direct neural control of the hypothalamus. It synthesis oxytocin and vasopressin and are transported to the posterior lobe of pituitary through axons. In females, oxytocin enhances contraction of smooth muscle cells in the wall of the uterus at the time of childbirth, and milk ejection from the mammary glands. Vasopressin stimulates the kidneys to reabsorb water and electrolytes into the blood by the distal tubules. It thereby reduces the loss of water through urine, hyposecretion of it leads to diabetes insipidus. Pineal gland secretes melatonin, which regulates the twenty-four hour rhythm of the body. 

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