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The Female Reproductive Cycle...Explained
If you’re a woman, the following portrait – or certain aspects of it – may ring a familiar bell:
Yesterday you were oddly, and perhaps irrationally, irritated by your coworker’s innocent mistake. Today you’re bloated and your face has broken out like it did when you were a teenager. Tonight you ate enough take-out to feed a family of three, your breasts hurt, and you started crying during a T.V. ad for toilet paper. If you’re a female, and some or all of these symptoms seem to occur on regular basis – say, every 28 days or so – you may be victim to a well-studied phenomenon called premenstrual syndrome (PMS).
Though the above scenario may fall on the more extreme end of the spectrum, many women suffer from symptoms of PMS at some time or another during their lives. Though it’s a well-documented syndrome, many people are unfamiliar with the mechanisms behind it. Nowadays, a commonly used phrase to explain or dismiss a woman’s moodiness is: “she must have PMS.” Women may be understandably annoyed at such an assumption (particularly when it’s inaccurate), and while somewhat amusing, it may point to a larger lack of understanding of women’s cycles. Men in particular may also view PMS as an unsubstantiated scapegoat for female moodiness, and question whether it is real biological phenomenon at all.
There has always been some mystery and romance associated with the female cycle, perhaps stemming from its synchrony with the cycle of the moon. But aside from that, many people (women included) may not know exactly how the female reproductive cycle operates – specifically, what hormones are involved, how they are controlled, why PMS occurs (including both the physical and behavioral symptoms), and when exactly in the cycle fertility is possible and impossible. This article aims to clarify how the female cycle works overall, and just how the changes to the body and behavior occur throughout the course of a month.
The Menstrual Cycle
The menstrual cycle, by definition, begins on the first day of a woman’s period (the day that bloody discharge begins), and ends on the day before the following menstrual period. The discharge occurs because the body is ridding itself of the preparations that it had made during the previous cycle in the event that pregnancy might occur. In other words, it is getting rid of the thick uterine lining it had made (which would have been a cozy spot for a fertilized egg to implant itself), and it is getting rid of the egg that went unfertilized during the previous cycle. With the new cycle the body will now begin to set itself up for once again releasing an egg and preparing for pregnancy. The phases of the reproductive cycle are dependent upon the interaction of several key hormones (see below).
Many people have heard of the two major hormones involved in the female reproductive cycle: estrogen and progesterone. Though these two hormones are indeed central players, there are also other hormones that are crucial to the cycle’s functioning – and all are ultimately under the control of two main brain regions. One area is the hypothalamus, which is important in basic bodily processes like hunger, sleep, and sexual arousal. The other is the pituitary gland, which is adjacent to the hypothalamus.
The hypothalamus releases a hormone called gonadotropin-releasing hormone (GnRH), which is an important hormone in both women and men.(1) This hormone signals the pituitary gland to make and release two additional hormones that actually signal the sex organs to start working: in women, these are follicle stimulating hormone (FSH) and luteinizing hormone (LH).(2) These hormones begin to rise prior to ovulation (the release of the egg from an ovary), and signal the body to begin preparing for ovulation and potential pregnancy.
FSH is mainly responsible for signaling the ovaries to begin preparing mature eggs, or more precisely, mature follicles, which include several types of supporting cells that nourish and surround the egg. LH is responsible for the mature follicle to be released from the ovary during ovulation. In the male, FSH is important in signaling the supportive cells in the testes to begin producing sperm cells, and LH is necessary for testosterone to be synthesized.(1)(3)
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