The reproductive cycle consists of three phases: 1) the menstrual phase; 2) the preovulatory phase; and 3) the postovulatory phase. During each phase there are changes in the ovaries and in the uterus in response to hormonal secretions from the pituitary (follicle-stimulating hormone [FSH] and luteinizing hormone [LH]) and gonads (estrogens and progesterone).
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Ovarian Cycle |
Uterine Cycle |
| Menstrual phase |
20 or more secondary follicles begin to enlarge; follicular fluid accumulates in the follicle |
Menstrual flow passes from uterus to exterior via vagina |
| Preovulatory phase |
Follicular phase because follicles are growing and developing; secondary follicles continue to grow; one follicle outgrows the others and becomes the dominant follicle; estrogen secretion increases; secretion of FSH decreases |
Proliferative phase because the endometrium is growing |
| Ovulation |
Rupture of the mature follicle; release of the secondary oocyte into the pelvic cavity |
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| Postovulatory phase |
Luteal phase; mature follicle collapses; if fertilization occurs, the corpus luteum continues past its normal two-week lifespan; if fertilization does not occur, the corpus luteum lasts for only two weeks and then degenerates; follicular growth then resumes and a new cycle begins |
Preparation of endometrium for fertilized ovum; if fertilization does not occur, the menstrual phase begins again |
