Tuesday, 13 August 2013

The Monthly Cycle

Before reading this post, I would suggest you start with my previous entry 'This is where it all starts' and work up, to undertand the context.

This is basically a general sketch of what takes place in a woman's body every month. The first thing to know is that everybody is different, and a ‘normal’ cycle can be anything from 21 to 35 days. They also tend to be more regular when we are younger.

The first day of the cycle is the day we start bleeding. It will last 3 to 5 days, but again, this varies from woman to woman. During bleeding, our estrogen levels are just a tenth of what they will be at their peak. The ‘blood’ is not actually blood- it is the lining of the womb (built up over the previous weeks) coming away, discarded because we’re not pregnant and therefore don’t need it. Sometimes it might seem like a lot of blood to loose, but it’s actually only around an egg-cup full on average.

As bleeding ends, the pituitary gland in our brain secretes a hormone called FSH (follicle stimulating hormone). The purpose of this is to tell our ovaries to prepare a few follicles, ready to produce an egg. As these grow, they produce more and more estrogen- which in turn, tells the lining of the womb to thicken again. This stage is called the follicular stage, and can last anywhere from 5 to 20 days, depending on the length of our cycle.
Usually only one egg will mature inside one follicle. As it reaches maturity it begins to secrete another hormone called progesterone. Next, the FSH is joined by another chemical produced in the pituitary gland- LH (luteinizing hormone), telling the follicle to release the egg. This is ovulation, and will usually occur midway through the cycle (so that would be day 10/11 in a short cycle, up to day 17/18 in a long cycle). It will take around seven days to journey from the ovary to the uterus… and it is during these days that we are most likely to get pregnant. Some women are able to tell when ovulation happens: they may be more horny than usual, or feel a slight cramping sensation in their lower stomach.

Now it’s all go for the uterus! Our bodies basically WANT to get pregnant at this point in our cycle (whether we consciously want to or not!) and so the uterus is preparing itself for a fertilised egg. This is the bit I find really interesting: while the womb lines itself with a soft, thick layer of cells, the ovarian follicle which housed the egg turns into something called a ‘corpus luteum’ and now has the job of producing the hormones needed to make the uterus ready for a baby to grow inside it. Progesterone is the main one, and is forty times it’s lowest level at this time! Estrogen, LH and FSH dip while progesterone rises sharply.

If the egg is fertilised (there is a window of around fourteen days after ovulation for this to take place), the body will continue to produce estrogen and progesteone. The egg itself will also produce another hormone called HCG (human chorionic gonadotropin) which is what home pregnancy tests pick up.

If the egg isn’t fertilised, estrogen continues to drop, and progesterone also drops. The corpus luteum shrinks and is reabsorbed, and we return to day one of the cycle when the lining of the womb begins to break down again.

Now you can probably understand why women tend to be labelled as ‘hormonal’! After puberty, men’s hormones settle and level off. Women, on the other hand, live with a constant shifting of hormones as our bodies prepare for pregnancy, and then ‘tidy up’ after themselves, ready to start all over again!

The menstrual cycle is powered by hormones. Every day the levels of each hormone will be different, and yet so predictable that a scientist could tell you exactly what day of your cycle you were on just by taking a biopsy. For example, LH is released in pulses by your brain every sixty to seventy minutes before ovulation, and only once every 200 minutes by the time your period is starting.

With a system so complex and intricate, it’s unsurprising to me that we often have problems with it!

And all of this is going on, every single day, without us even being aware of it!

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