Female Reproductive System (cont.)
What Happens During the Menstrual Cycle?
Females of reproductive age experience cycles of hormonal activity that
repeat at about one-month intervals. (Menstru means "monthly"; hence the term
menstrual cycle.) With every cycle, a woman's body prepares for a potential
pregnancy, whether or not that is the woman's intention. The term menstruation
refers to the periodic shedding of the uterine lining.
The average menstrual cycle takes about 28 days and occurs in phases: the
follicular phase, the ovulatory phase (ovulation), and the luteal phase.
There are four major hormones (chemicals that stimulate or regulate the
activity of cells or organs) involved in the menstrual cycle:
follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone.
Follicular Phase
This phase starts on the first day of your period. During the follicular phase of the menstrual cycle, the following events occur:
- Two hormones, follicle stimulating hormone (FSH) and luteinizing hormone (LH)
are released from the brain and travel in the blood to the ovaries.
- The hormones stimulate the growth of about 15-20 eggs in the ovaries each in
its own "shell," called a follicle.
- These hormones (FSH and LH) also trigger an increase in the production of
the female hormone estrogen.
- As estrogen levels rise, like a switch, it
turns off the production of follicle-stimulating hormone. This careful balance
of hormones allows the body to limit the number of follicles that complete
maturation, or growth.
- As the follicular phase progresses, one follicle in one ovary becomes
dominant and continues to mature. This dominant follicle suppresses all of the
other follicles in the group. As a result, they stop growing and die. The
dominant follicle continues to produce estrogen.
Next: Ovulatory phase »
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