Ovarian and Menstrual Cycle in Human female скачать в хорошем качестве

Ovarian and Menstrual Cycle in Human female

There are two closely linked reproductive cycles in human females. The term menstrual cycle refers specifically to the changes that occur about once a month in the uterus; therefore it is also called the uterine cycle. The cyclic changes in the uterus are controlled by the ovarian cycle, cyclic events that occur in the ovaries. Thus, the female reproductive cycle is actually one integrated cycle involving two organs, the uterus and the ovaries. The Ovarian Cycle The ovarian cycle begins with the release from the hypothalamus of GnRH, which stimulates the anterior pituitary to secrete small amounts of FSH and LH. Follicle-stimulating hormone (as its name implies) stimulates follicle growth, the cells of the growing follicles start to make estrogen or estradiol. When estradiol secretion by the growing follicle begins to rise steeply, the FSH and LH levels increase markedly.T The follicular phase ends at ovulation, about a day after the LH surge. In response to both FSH and the peak in LH level, the follicle and adjacent wall of the ovary rupture, releasing the secondary oocyte. Luteinizing hormone stimulates the follicular tissue left behind in the ovary to transform into a corpus luteum, a glandular structure. Prior to ovulation, ovarian steroid hormones stimulate the uterus to prepare for support of an embryo. Estradiol secreted in increasing amounts by growing follicles signals the endometrium to thicken. In this way, the follicular phase of the ovarian cycle is coordinated with the proliferative phase of the uterine cycle. corpus luteum stimulate maintenance and further development of the uterine lining, including enlargement of arteries and growth of endometrial glands. These glands secrete a nutrient fluid that can sustain an early embryo even before it implants in the uterine lining. Thus, the luteal phase of the ovarian cycle is coordinated with the secretory phase of the uterine cycle.