Positive feedback of oestrogen and the sudden increase of LH in the pre-ovulatory period
During the cycle, at that time oestrogen has its own positive feedback that stimulates the pituitary to secrete LH, and a small stimulus to release FSH, which is a stark contrast to the negative feedback that occurs during pregnancy. of the menstrual cycle.
For reasons that are not completely understood, the anterior pituitary gland secretes large amounts of LH 1-2 days before ovulation. This effect is described in
Experiments have shown that the amount of oestrogen in the female body above the critical level for 2-3 days in the last half of the first half of the menstrual cycle accelerates the development of the follicles as well as sharply increases the secretion of the ovaries. . During this phase, the secretion of FSH and LH from the first anterior pituitary decreases slightly, then the secretion of LH increases abruptly by 6-8-fold and the secretion of FSH increases 2-fold. The sudden increase in LH levels causes ovulation to occur.
The cause of the sudden increase in LH secretion remains unclear. However, a few reasons are given:
Figure: Feedback on adjustment of the hypothalamic-satellite axis in women. The stimulant effect is shown by plus signs; negative feedback and inhibitory effects are shown with a minus sign. Oestrogens and progestins exert both negative and positive feedback on the pituitary and hypothalamus depending on the phase of the menstrual cycle. Inhibin produces negative feedback on the anterior pituitary, while activation has the opposite effect, stimulating FSH secretion from the anterior pituitary.
1. During the cycle, at that time, oestrogen has its own positive feedback that stimulates the pituitary to secrete LH, and a small stimulus to release FSH, which is a clear contrast to the negative feedback that occurs during the phase. the remainder of the menstrual cycle.
2. The granulosa cells in the follicle begin to secrete small and gradually increasing amounts of progesterone each day until LH peaks and possibly, for this reason, stimulates LH secretion.
If there is no LH peak before ovulation, the egg will not be able to be released.