Zoology · Ch 2 — Human Reproduction
Menstrual Cycle
Menstrual Cycle
The menstrual (ovarian) cycle is the roughly 28-29 day rhythm that recurs continuously through a woman's reproductive life, starting at menarche (puberty) and continuing until menopause, pausing only during pregnancy. One full cycle is measured from the start of one menstrual period to the start of the next, and across it the endometrium undergoes cyclic changes every month; a regular, cyclic pattern of menstruation is itself taken as a sign that the reproductive system is functioning normally. Two things happen in parallel throughout the cycle — a follicle develops and is released from the ovary, and the endometrium is built up and then shed in the uterus — both driven by the pituitary gonadotropins FSH and LH acting together with the ovarian …
What this figure shows. A composite multi-panel chart plotted against the same 28-day timeline (days 1 through 28) across four aligned rows. The top row plots FSH and LH secreted by the anterior pituitary as two curves, with the day-14 LH surge marked as the trigger for ovulation. The second row shows the corresponding events in the ovary: several follicles starting to develop, narrowing to a single mature follicle, ovulation, formation of the corpus luteum, and its eventual degeneration into the corpus albicans. The third row plots the ovarian hormones oestrogen and progesterone as curves rising and falling across the same days. The bottom row shows events in the endometrium of the uterus — bleeding and sloughing (menstruation) at the start, then a highly proliferated and vascularised endometrium building up in thickness through the rest of the …