Menstrual Cycle Physiology: Ovarian Cycle – Luteal Phase Explained • The LH surge can be thought of as only providing enough "battery power" for the corpus luteum to run and make progesterone for 14 days, which is why the luteal phase is a fixed length. • The timing and function of estrogen and progesterone during the ovarian cycle are also important to the uterine cycle (see Uterine Cycle slide) Besides ovulation, the Day 14 surge in LH also stimulates a process called "luteinization": the maturation of the ruptured follicle's granulosa cells into the corpus luteum -> Corpus luteum begins to secrete a large amount of progesterone and a smaller amount of estrogen -> The combination of high progesterone and estrogen negatively feed back on hypothalamus and anterior pituitary -> Decreased Production of GnRH, FSH, and LH • Decreased FSH means no new follicles grow in the ovary in this phase • Decreased LH means less stimulation for continued corpus luteum growth => • If implantation does occur, HCG (human chorionic gonadotropin) maintains the corpus luteum so progesterone (and therefore endometrium) will be maintained • If no implantation of embryo, corpus luteum degenerates after 14 days, allowing GnRH/FSH/LH to restart the Ovarian Cycle #MenstrualCycle #OvarianCycle #pathophysiology #LutealPhase #endocrinology
