The luteal phase usually lasts 14 days. Thus, ovulation day + 14 days (luteal phase) is the day of menstruation. In a typical 28 day menstrual cycle, days 15-28 are considered the luteal phase.
After stimulating ovulation, LH causes the follicle to become the corpus luteum. This secretes progesterone.
After ovulation, Progesterone is secreted by the corpus luteum. Progesterone works to stimulate secretory and vascular activity of the endometrium, preparing for implantation of an embryo.
After ovulation, progesterone provides negative feedback to the anterior pituitary gland, preventing release of FSH and LH. This is to prevent the development of multiple follicles.
Nearly 14 days after ovulation, when egg fertilization does not occur, the corpus albicans is formed. The corpus luteum degenerates from macrophage breakdown, and turns into the corpus albicans, which is a mass of fibrous scar tissue. As the corpus albicans is formed, progesterone production slowly declines.
Along with progesterone secretion, estrogen secretion also decreases with formation of the corpus albicans.
A swift decrease in progesterone causes the new vascular in the endometrium (which forms due to progesterone) to regress. Without vascular support, along with decreasing estrogen levels, the endometrium is no longer supported and sloughs within the uterus. This endometrial sloughing and bleeding is menses.
After the onset of menorrhea, or the "period," a new follicular cycle begins (at or around day 28), beginning with GnRH causing the release of FSH and LH, stimulating new follicles to develop.
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