Menstrual Cycle

Keywords

Menstrual cycle, menstruation, period, ovulation, reproduction system, uterus lining, follicle stimulating hormone (FSH), lutenising hormone (LH), oestrogen, progesterone, pituitary gland, ovaries.

Introduction

Once a month (sometimes earlier, sometimes later) a woman goes through a period. This is part of a whole cycle over the course of a month where a woman's body changes for reproduction.

What Actually Happens?

Be ready for some graphic details here. At least, you may find them unsettling. But they are a natural process, so it needs to be discussed.

OK, so we start at the beginning. And the beginning is when a woman first starts to discharge blood from their uterus. The reason for this is because before menstruation, the lining of the uterus is prepared for pregnancy. Menstruation occurs because there is no pregnancy going forward, so this results in the lining being shed.

The process of the uterus lining being shed lasts for around 7 days. Sometimes this can vary, and it can fluctuate between 5 and 10 days, depending on the woman, as every woman's body is different.

Interesting fact: a female's first period is called a menarche. This is taken from Greek: men = month, arkhe = beginning. Once the menarche has occurred, a female will not start to ovulate until between a year and 18 months after this.

There are four hormones that help with menstruation:

• Lutenising hormone (LH): stimulates the release of the egg.
• Follicle stimulating hormone (FSH): this helps with maturing the egg in the ovary.
• Oestrogen: repairs and thickens the uterus lining. The production of oestrogen also stops the production of FSH once an egg has been sent to mature.
• Progesterone: maintains the uterus lining during the middle and later part of pregnancy.

Hormone Production

Two hormones, FSH and LH, are created in the pituitary gland. The other two, oestrogen and progesterone, are created in the ovaries.

If a woman falls pregnant, the placenta creates the hormone progesterone, as it needs a lot of this to maintain the uterus.

The entire process of menstruation begins on the first day of the uterus shedding the lining, until the day before the next cycle begins.

Corpus Luteum

When the follicles in a woman's ovary become dominant, and they are ready to release an egg, what's left behind changes. It falls in on itself, and releases a different hormone to what it was doing during incubation of the egg. This is what is known as the corpus luteum.

But what does it do?

Well, actually, it's a gland structure that remains only temporarily. I said it changes the hormone it releases when the egg is free; that is changed to oestrogen and progesterone. They release these hormones to aid the body in preparation for conception. They build up the lining in the uterus and help to maintain that lining if conception is successful.

When the corpus luteum breaks down, it leaves behind scar tissue in the form of cartilage. This is then called corpus albicans. It sticks to the ovaries for a while, before being destroyed by macrophages of the immune system.