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December 01, 2016 00:09

Hormonal regulation of the menstrual cycle

menstrual cycle reflects the activity of the hypothalamic-pituitary-ovarian axis, which is shown structural and functional changes in the reproductive tract: the uterus, fallopian tubes, endometrium, vagina.Each cycle ends with menstruation, the first day is considered the beginning of the cycle.

During the first part of the menstrual cycle (follicular phase) FSH secreted by the anterior pituitary gland and stimulates the production of estradiol granulёznymi ovary cells.FSH and estradiol cause proliferation of these cells and increases the secretion of estradiol.These hormones stimulate LH receptors.Estradiol acts on the uterine endometrium, causing its thickening and vascularization, thus preparing it for egg implantation.As maturation of follicles in them and in blood increases inhibin level which provides selectively-ingi biruyuschee effect on FSH secretion.

peak estradiol concentrations in the blood that falls in the middle of the menstrual cycle (day 14), is launching a wave of LH surge from the

pituitary gland.LH stimulates ovulation (release of an egg from a mature follicle).The remaining cells in the follicle postovulatory formed corpus luteum, which begins to secrete progesterone and estradiol.Progesterone exerts an inhibitory effect on the secretion of inhibin.

During the second, luteal, phase progesterone together with estradiol cause even greater thickening of the endometrium.There is enhanced vascularization of the endometrium cells and their differentiation, the cells become secretory.

After about 1 week after the corpus luteum formation it begins to reverse the development and secretes less of estradiol and progesterone.By day 28 of the menstrual cycle, levels of ovarian steroids becomes inadequate to sustain life thickened endometrium and it would be destroyed, which leads to menstruation.The bleeding lasts 3-5 days.Low levels of estradiol and progesterone in the end of the cycle is removed (on the principle of negative feedback) inhibition of GnRH secretion by the hypothalamus.The level of GnRH in the hypothalamus increases, which stimulates the secretion of FSH and LH by the pituitary gland, and the menstrual cycle begins again.