How can fsh help produce an egg?

Answer 1

FSH is the major survival factor that rescues the follicles from atresia (programmed death of the somatic cells of the follicle and oocyte).

In the luteal-follicle phase transition period the serum levels of progesterone and estrogen (primarily estradiol) decrease and no longer suppress the release of FSH, consequently FSH peaks at about day three (day one is the first day of menstrual flow).

The cohort of small antral follicles is normally sufficiently in number to produce enough Inhibin B to lower FSH serum levels. As a woman nears perimenopause the number of small antral follicles recruited in each cycle diminishes and consequently insufficient Inhibin B is produced to fully lower FSH and the serum level of FSH begins to rise. When the follicle matures and reaches about 10 mm in diameter it starts to secrete significant amounts of estradiol.

Normally in humans only one follicle becomes dominant and survives to ovulate, the remaining follicles in the cohort undergo atresia. The increase in serum estradiol levels cause a decrease in FSH production by inhibiting GnRH production in the hypothalamus.

The decrease in serum FSH level causes the smaller follicles in the current cohort to undergo atresia as they lack sufficient sensitivity to FSH to survive. Occasionally two follicles reach the 10 mm stage at the same time by chance and as both are equally sensitive to FSH both survive and grow in the low FSH environment and thus two ovulations can occur in one cycle possibly leading to non identical twins.