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# C. THE LUTEAL PHASE The luteal phase extends from the time of ovulation until menstruation, and lasts about 14 days. ## Corpus luteum (CL) formation After ovulation, under LH influence, the granulosa cells of the ruptured follicle undergo luteinization. These luteinized granulosa cells, along...

# C. THE LUTEAL PHASE The luteal phase extends from the time of ovulation until menstruation, and lasts about 14 days. ## Corpus luteum (CL) formation After ovulation, under LH influence, the granulosa cells of the ruptured follicle undergo luteinization. These luteinized granulosa cells, along with surrounding theca cells, capillaries, and connective tissue, form the CL. The luteinized cells of the CL have a vacuolated appearance due to the accumulation of a yellow pigment (lutein), thus giving the CL its name. ## The Menstrual Cycle and Associates Disorders The corpus luteum (CL), in response to continuous pituitary LH stimulation, produces large amounts of progesterone (P) and smaller amounts of estrogen (E2), and some inhibin. This leads to a decrease in FSH and LH levels, inhibiting the growth of new follicles in the luteal phase. Progesterone prepares the endometrium for possible embryo implantation. ## Fate of the CL The luteal phase lasts approximately 14 days. The CL's lifespan is about 9 days, after which it undergoes luteolysis, transforming into the avascular corpus albicans. * **In the absence of pregnancy:** The CL undergoes apoptosis (programmed cell death) and stops producing progesterone (P) 12-14 days after ovulation. Gonadotropin inhibition is released, and FSH levels begin to rise. * **In the presence of pregnancy:** Human chorionic gonadotropin (hCG), produced by the trophoblast, maintains progesterone (P) secretion from the CL until placental steroidogenesis is established (around the 8th week of gestation). ## End of the luteal phase As the CL degenerates, levels of E2, P, and inhibin fall. The pituitary gland is released from the negative feedback effect of these hormones, and FSH levels rise. Follicles in the preantral stage are rescued from atresia (programmed cell death), initiating a new ovarian and menstrual cycle.