Library · Physiology
Menstrual cycle
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The menstrual cycle is the preparation that the female reproductive tract repeats over and over to allow ovulation and, if pregnancy occurs, support it.
The command comes from above. The hypothalamus, a small area of the brain, releases gonadotropin-releasing hormone in pulses. Those pulses signal the anterior pituitary, the gland that hangs just below it, and the pituitary responds by sending two hormones to the ovary: follicle-stimulating hormone and luteinizing hormone.
And here is what almost no one realizes: it is not one cycle, it is two running at the same time. Two interlocking clocks: one in the ovary, one in the endometrium. The ovarian cycle has a follicular phase, ovulation, and a luteal phase. The endometrial one, the cycle of the lining on the inside of the uterus, has a proliferative, a secretory, and a menstrual phase.
As for length, there is a reference point: cycles that come every 24 to 38 days are considered normal. And they do have an end date: they stop at menopause.
In brief
The menstrual cycle periodically prepares the female reproductive tract for ovulation and a possible pregnancy.
It starts in the hypothalamus, which releases gonadotropin-releasing hormone in pulses; the anterior pituitary sends follicle-stimulating and luteinizing hormones to the ovary.
There are two cycles: the ovarian one, with a follicular phase, ovulation, and a luteal phase, and the endometrial one, with proliferative, secretory, and menstrual phases.
Two interlocking clocks: one in the ovary, one in the endometrium.
A cycle every 24 to 38 days is normal; cycles stop at menopause.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Menstrual Cycle, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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