5 Describe with hormones in cyclic development in ovary and uterus
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Answers
Answer:
Progesterone levels rise during the luteal phase of the ovarian cycle and the secretory phase of the uterine cycle. Menstruation occurs just after LH and FSH levels peak. Menstruation occurs after progesterone levels drop. Estrogen levels rise before ovulation, while progesterone levels rise after.
Explanation:
Pituitary and Ovarian Hormones Control the Ovarian Cycle
1
The ovarian cycle is controlled by the interplay of hormones from the pituitary gland and from the ovary itself. A few days before the beginning of the cycle, the anterior pituitary begins to increase its secretion of two hormones: follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
2
FSH and LH stimulate ovarian follicles to grow. As the follicles grow, they begin to secrete estrogen. During this phase of the cycle, the increasing levels of estrogen feed back on the pituitary to inhibit the release of additional FSH and LH. During the next week, the levels of FSH and LH drop.
3
Beginning around day 12, the increasing levels of estrogen suddenly have the opposite effect on the pituitary gland. Instead of exerting a negative feedback on the pituitary, these hormones now exert a positive feedback, stimulating the pituitary to release FSH and large amounts of LH.
4
LH reaches a peak at day 14 of the ovarian cycle. This LH surge triggers the mature follicle to rupture and release the eggÑthe process of ovulation. LH then triggers the remaining follicle cells to differentiate into the corpus luteum, which secretes estrogen and progesterone.
5
The corpus luteum remains in the ovary, secreting estrogen and progesterone, for the last two weeks of the cycle. At this point in the cycle, these hormones again inhibit the release of FSH and LH. A decline in FSH and LH restricts follicles from beginning to develop during the second half of the cycle.
6
LH (or a hormone produced by an implanted embryo) is required to maintain the life of the corpus luteum. At the end of the cycle, if an embryo has not implanted, the corpus luteum degenerates. When the corpus luteum degenerates, it no longer releases estrogen and progesterone.
Ovarian Hormones Control the Uterine Cycle
1
The ovarian and uterine cycles are tightly coordinated. Hormones secreted by the ovary at different phases of the ovarian cycle trigger changes in the uterine lining. For example, at the beginning of the cycles, the levels of estrogen and progesterone are too low to maintain the uterine lining, and menses begins.
2
About a week into the ovarian cycle, the developing follicle increases its secretion of estrogen, and estrogen levels in the body begin to rise. This hormone triggers the cells of the uterine lining to proliferate, and the lining becomes thicker.
3
Just before ovulation, the level of estrogen in the body has reached its peak. Afterward, the follicle cells remaining in the ovary develop into the corpus luteum, a structure that releases estrogen and progesterone. The hormones maintain the uterine lining at a peak thickness and preparedness for embryo implantation.
4
At the end of the cycle, if the egg is not fertilized or has not implanted, the corpus luteum breaks down and stops releasing estrogen and progesterone. Without these hormones, the uterine lining also breaks down, initiating menses.