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The female menstrual cycle

The first half of the cycle (1st-14th day).

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The hormones of pituitary gland influence functioning of female sexual organs, and as a result of that, a follicle matures in the ovary. The larger the follicle is, the sooner the ovulation happens. At the same time, oestrogen (E2) is increasingly produced in the follicle. This hormone prepares the endometrium (uterine lining) for the egg cell and opens the cervix for several millimetres. In addition to that, they make sure that enough cervical mucus is produced, which enables the sperms to enter into the uterus.

An important fact that the uterus performs contractions - has become known only recently. These contractions can be measured with the help of new devices and can be depicted by ultrasound. They increase in the middle of the cycle and proceed from the lower uterus to the uterine cavity and from there to the ovaries. These contractions support transportation of sperm cells.

Middle of the cycle (14-16th day)

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The maximum production of oestrogen by a mature follicle causes release of LH from the pituitary gland. This initiates final maturation processes, which leads to ovulation. The fallopian tube of the respective side catches the mature egg, which is capable of being fertilized and transports it towards the uterus.

The purposeful contractions become more intensive. They help to pull the sperms from the vagina and to transport them towards the egg ready for ovulation. This mechanism has been clarified only in the recent years. If the sperms had to penetrate to the fertilisation spot only by own mobility, they would need many days for that.

On the 6th to the 7th day after the ovulation

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the embryo nidates (becomes implanted) in the respectively prepared endometrium (uterine lining). The embryo produces hormonal signals (pregnancy hormone hCG) and thus sends the signal of nidation to the ovary. The yellow body, the “leftover” of the ruptured follicle, remains and produces the hormone progesterone, which is in charge of maintaining the pregnancy.

 

Second half of the cycle (appr. 17th -18th day)

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The egg in the fallopian tube has not been fertilized. The ovary can recognise it because there are signals coming from the uterus. The yellow body develops but disappears after 10 to 14 days. The content of progesterone in the blood decreases and endometrium is removed with bleeding. The first day of the new cycle has begun.