Human Female Reproductive Cycles
In a sexually-mature human female there is a highly coordinated and interdependent series of cycles that take place. These cycles include; the release of pituitary gonadotropins (LH and FSH surges) into the bloodstream, the ovarian steroid response cycle (estrogen synthesis and also later progesterone synthesis), the oocyte meiotic maturation/ovulation response cycle and the uterine endometrium cycle of proliferation and destruction (menses). These cycles repeat approximately every 28-29 days if there is no pregnancy.
If fertilization of the egg takes place within 1-2 days of ovulation (days 14-15 of the cycle) and pregnancy is successful, the uterine wall is maintained and the cycles stop. The implanted blastocyst trophoblast cells synthesize amd release hCG which maintains the corpus luteum and progesterone synthesis.
