"Caught between the unborn and the living, a writer struggles to maintain both depth and surface." -Lu Chi (from Wen Fu)

Writing Prizes:
Winning Essays

Three Generations Prize for Writing in the Sciences

"The Menstrual Cycle"
Elizabeth Eisenhardt '00

With the advent of their first menstrual cycle, women realize that not only are they now capable of having children, but that this inevitable biological process will occur repeatedly each month until they reach menopause. What is not as obvious a thought, is exactly how the cycle's mechanisms and controls continue each month in the human body. The supposedly simple cycle occuring once a month is incredibly intricate and detailed, with numerous hormonal controls and checkpoints. Says prominent menstrual cycle researcher S.S.C. Yen,

The initiation of puberty depends on a complex series of events that occur within the brain and appears to require interactive participation of neuronal circuits and glial networks as well as peripheral endocrne-metabolic signals (1999, pg.191).

In this paper, I will present a review of the menstrual cycle, considering in particular two hypotheses surrounding the cycle's mechanics: Knobil's pelvic clock hypothesis and Derin's opioid hypothesis. I will present a digram which shows the proposed important sequence of neurons involved in the cycle and how they might be interconnected. In conclusion I will produce a summary hypothesis of what current research implies are the mechanisms of the menstrual cycle. Please note that many of the paper's details were provided in class lecture (Coyne, M. 1999).

It is necessary to begin with a basic explanation of the major events in the menstrual cycle before discussing the complex interactions bringing about such events. The menstrual cycle can be divided into three stages: 1) preovulatory (follicular), 2) ovulatory, and 3) postovulatory. The preovulatory phase is of variable length for each woman with day one of the cycle considered the first day of menses: an event which results from the uterine lining sloughing off in the absence of pregnancy (Norris, 1980). Menses usually occurs for a period of five days, after which the preliferative stage begins. During this time, the endometrium is stimulated by estradiol and the follicle is maturing (Norris, 198). The menses and the proliferative stage combined make up the follicular stage of the menstrual cycle (Norris, 1980). Fourteen days before the onset of menses, ovulation usually occurs. This is preceded by a rise in estrogen levels, which is followed by a peak in luteinizing hormone (LH) and follicle stimulting hormone (FSH) (Norris, 1980). LH is crucial for ovulation and subsequent increase in estrogen and progesterone secretion, while FSH is needed for preovulatory growth and development of the follicle and the concomitant follicular secretion of estrogen. During ovulation, the ovary release the egg and the corpus luteum is formed from the remaining cells. Following ovulation, the cycle enters the luteal phase whereby the developed corpus luteum secretes estrogen and progesterone (Norris, 1980). Eventually, in the absence of a fertilized egg, the corpus luteum degenerates, thus beginning the menses.

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• Lynne Viti and Wini Wood
• Wellesley College Writing Program
• Created by: Karyn Lu '01
• Date Created: June 29, 2000
• Expires: July 31, 2009

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