Uterine (Menstrual) Cycle Stages of the menstrual cycle Menstrual phase Proliferative stage Secretory stage

Menstrual Cycle: Phase 1 Menstrual phase Days 1–5 Outer layer of the endometrium is sloughed Bleeding occurs for 3–5 days (female’s “period”) Low levels of estrogen and progesterone

Menstrual Cycle: Phase 2 Proliferative stage Days 6–14 (AKA: The follicular phase) FSH is stimulating the follicle to mature As the follicle matures it is releasing estrogen Estrogen is causing the endometrium to thicken Ovulation occurs at the end of this stage (Day 14) A surge in LH causes ovulation

Menstrual Cycle: Phase 3 Secretory stage Days 15–28 (AKA: The luteal phase) Corpus luteum develops Corpus luteum releases progesterone Levels of progesterone increase the blood supply to the endometrium (thickening the lining)

Secretory stage (continued) If fertilization does occur Embryo produces a hormone (HCG) that stops the corpus luteum from disappearing If fertilization does NOT occur Corpus luteum degenerates

Ovarian Cycle Figure 16.12c

Uterine (Menstrual) Cycle Figure 16.12d