Figure 1

Changes in the reproductive tract throughout the menstrual cycle. Follicle stimulating hormone (FSH) from the pituitary promotes follicle growth in the ovary. These follicles produce estrogen (E). In response to E, the functional is layer of the uterine epithelium and the stratified layer of the vaginal epithelium thicken as the infindibulum of the fallopian tube comes in contact with the ovary. The luteinizing hormone (LH) surge from the pituitary causes the dominant follicle to ovulate. The remaining follicular cells develop into a corpus luteum that produces E and progesterone (P). In turn, P promotes more proliferation within the uterus and vagina, and cornification in the vagina. The uterotubal junction of the fallopian tube widens to allow the passage of the ovulated oocyte or fertilized embryo. Reduced E and P levels induce atrophy of vaginal epithelium and menstruation of the uterine functionalis layer.