1. Copyright © 2006, Elsevier Inc. All rights reserved C HAPTER 3 The Menstrual Cycle

2. Copyright © 2006, Elsevier Inc. All rights reserved F IGURE 3-1 T HE THREE PHASES OF A 28- DAY MENSTRUAL CYCLE SHOWING OVARIAN AND UTERINE EVENTS. T HE FIRST TWO PHASES OF THE OVARIAN CYCLE ( EARLY AND LATE FOLLICULAR PHASE ) REPRESENT GROWTH OF SELECTED OVARIAN FOLLICLES. T HE LUTEAL PHASE, WHEN THE CORPUS LUTEUM IS PRESENT, LASTS FROM OVULATION TO THE BEGINNING OF THE NEXT CYCLE. T HE UTERINE CYCLE DESCRIBES IMPORTANT UTERINE EVENTS DURING THE 28- DAY CYCLE. T HE MENSTRUAL PHASE, OR PERIOD OF MENSTRUAL FLOW, IS FOLLOWED BY THE PHASE OF ENDOMETRIAL PROLIFERATION. A FTER OVULATION, THE UTERUS ENTERS THE SECRETORY PHASE. B OTH OVARIAN AND UTERINE EVENTS ARE DEPICTED IN THE MORE COMMONLY USED COMBINED MENSTRUAL CYCLE ( LOWER FIGURE ). H ERE, DAY 1 IS THE BEGINNING OF THE MENSTRUAL PHASE, WHICH LASTS ABOUT 5 DAYS. T HE MENSTRUAL PHASE IS FOLLOWED BY THE FOLLICULAR PHASE, WHICH ENDS AT OVULATION ON ABOUT DAY 14. N EXT IS THE LUTEAL PHASE, ENDING 14 DAYS LATER WITH THE BEGINNING OF MENSTRUATION. T HE COMBINED MENSTRUAL CYCLE WILL BE USED IN THE TEXT

3. Copyright © 2006, Elsevier Inc. All rights reserved F IGURE 3-2 A VERAGE BLOOD LEVELS OF HORMONES DURING A 28- DAY MENSTRUAL CYCLE, ALONG WITH CHANGES IN THE OVARIES AND UTERINE ENDOMETRIUM. N OTE THAT AN ESTRADIOL PEAK PRECEDES THE LH SURGE. T HE RATIO OF ESTRADIOL TO PROGESTERONE IS HIGH DURING THE FOLLICULAR PHASE AND LOWER DURING THE LUTEAL PHASE. T HE OVARIES ALSO SECRETE SMALL AMOUNTS OF ANOTHER ESTROGEN ( ESTRONE ), ANDROGENS, AND 17- HYDROXYPROGESTERONE ( NOT SHOWN ). L EVELS OF PROGESTERONE ARE IN NANOGRAMS ( ONE THOUSANDTH OF A MILLIGRAM ) AND OF ESTRADIOL IN PICOGRAMS ( ONE THOUSANDTH OF A NANOGRAM ). L EVELS OF FSH AND LH ARE IN MILLI - INTERNATIONAL UNITS ( ONE THOUSANDTH OF AN INTERNATIONAL UNIT ). A N INTERNATIONAL UNIT IS AN AMOUNT OF A HORMONE THAT PRODUCES A GIVEN BIOLOGICAL RESPONSE IN A TARGET TISSUE. A LTHOUGH AVERAGE FSH AND LH BLOOD AMOUNTS ARE SHOWN, THE LEVELS OF THESE HORMONES AND G N RH EXHIBIT HOURLY PULSES (F IG. 3-4).

4. Copyright © 2006, Elsevier Inc. All rights reserved B OX 1: W HY W OMEN M ENSTRUATE

5. Copyright © 2006, Elsevier Inc. All rights reserved F IGURE 3-3 T HE EFFECT OF INCREASING BLOOD LEVELS OF ESTRADIOL DURING THE FOLLICULAR PHASE OF THE MENSTRUAL CYCLE ON SECRETION OF GONADOTROPIN (FSH AND LH) FROM THE PITUITARY. N OTE THAT IN THE EARLY FOLLICULAR PHASE (EFP), ESTRADIOL LEVELS ARE LOW AND GONADOTROPIN OUTPUT IS HIGH DUE TO THE ABSENCE OF NEGATIVE FEEDBACK OF ESTRADIOL ON GONADOTROPIN SECRETION. I N THE MIDFOLLICULAR PHASE (MFP), ESTRADIOL LEVELS ARE MODERATELY HIGH AND EXERT A NEGATIVE FEEDBACK ON GONADOTROPIN SECRETION. I N THE LATE FOLLICULAR PHASE (LFP), THE VERY HIGH ESTRADIOL LEVELS NOW EXERT A POSITIVE FEEDBACK ON GONADOTROPIN SECRETION, RESULTING IN THE LH SURGE

6. Copyright © 2006, Elsevier Inc. All rights reserved F IGURE 3-4 T HE PATTERN OF HOURLY PULSES OF LH AND FSH IN THE BLOOD DURING THE MENSTRUAL CYCLE

7. Copyright © 2006, Elsevier Inc. All rights reserved F IGURE 3-5 V ARIATIONS IN LENGTH OF MENSTRUAL CYCLE PHASES. N OTE THAT THE LENGTH OF THE LUTEAL PHASE IS USUALLY 14 DAYS. L ENGTHS OF THE FOLLICULAR PHASES OF THESE CYCLES ARE 6, 9, AND 16 DAYS. T HE LENGTH OF THE MENSTRUAL PHASE, ALTHOUGH SHOWN AS CONSTANT HERE, CAN VARY.

8. Copyright © 2006, Elsevier Inc. All rights reserved B OX 2: B ODY F AT AND S ECONDARY A MENORRHEA