Oxytocin is secreted mainly by the paraventricular nucleus and a small quantity is secreted by the supra- optic nucleus in the hypothalamus. And it is transported from hypothalamus to posterior pituitary through the nerve fibers of hypothalamo-hypophyseal tract.
In the posterior pituitary, oxytocin is stored in nerve endings of hypothalamo-hypophyseal tract. When suitable stimuli reach the posterior pituitary from hypothalamus, oxytocin is released into the blood. Oxytocin is secreted in both males and females. It's a polypeptide, having 9 amino acids.
Actions in Females
In females, oxytocin acts on mammary glands and uterus.
Action of oxytocin on mammary glands
It causes ejection of milk from the mammary glands. Ducts of the mammary glands are lined by myoepithelial cells. Oxytocin causes contraction of myoepithelial cells and squeezes the milk from alveoli of mammary glands to the exterior through duct system and nipple. The process by which milk is ejected from the alveoli of mammary glands is called milk ejection reflex or milk let-down reflex.
Action on pregnant uterus.
Throughout the period of pregnancy, oxytocin secretion is inhibited by estrogen and progesterone. At the end of pregnancy, secretion of these two hormones decreases suddenly and the secretion of oxytocin increases. Oxytocin causes contraction of uterus and helps in expulsion of fetus.
Action on non-pregnant uterus
Action of oxytocin on non-pregnant uterus is to facilitate the transport of sperms through female genital tract up to fallopian tube by producing the uterine contraction during sexual intercourse.
Action in Males
In males, release of oxytocin increases during ejaculation. It facilitates release of sperm into urethra by causing contraction of smooth muscle fibers in reproductive tract particularly vas deferens.
Comentarios