APII Study Guides

Menstrual Cycle Study Guide


Hormonal Event

Ovarian Cycle

Uterine Cycle


Gradual increase in LH, FSH production early, maintained at relatively low level through day 5. Estrogen production begins to pick up. Several ovarian follicles develop into secondary follicles.


(Follicular phase)

Progesterone levels are too low to maintain endometrial tissue. Most of the endometrial lining is shed (menstrual flow).

(Menstrual phase)


Rapidly increasing estrogen levels. LH and FSH surge at the end of this phase (day 14) One follicle develops into a fully mature vesicular follicle. Ovulation occurs on day 14 in response to LH surge.

(Follicular phase)


Endometrial lining rebuilds itself. Number and size of cells, spiral arteries, and glands enlarge due to estrogen.

(Proliferative phase)

15 - 28

Progesterone secretion by the corpus luteum increases rapidly, is maintained for several days, and then drops off rapidly as the corpus luteum degenerates. Corpus luteum secretes progesterone. (See left)

(Luteal phase)

Progesterone causes spiral arteries to develop, increasing the blood supply to the endometrium. Uterine glands enlarge, coil, and secrete nutritious glycoproteins into the uterine lumen which nourish the developing embryo until implantation

(Secretory phase)

Post 28 days, if implantation occurs

Human chorionic gonadotropin (HCG) is secreted by developing embryo. HCG maintains the corpus luteum. Continued production of progesterone maintains the uterine lining for the early part of pregnancy



Uterine cycle

Homonal Changes