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Function of Female Reproductive System
Normally, the menstrual cycle is 25 to 28 days long, and the first day of the menstrual cycle is calculated from the start of menstrual period. One menstrual cycle is calculated as the start of first day of period until before the start of next period. Accurately knowing your menstrual cycle is important for the success of your pregnancy.
The menstrual cycle can be roughly divided into three phases. The period from the start of development of the follicle to the maturation of the follicle is called the “follicular phase”, the period when the mature follicle is discharged from the ovary is called the “ovulation period”, and the period when the follicle after ovulation becomes the corpus luteum is called the “luteal phase”.
The menstrual cycle is regulated by multiple hormones. When menstruation begins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are a type of gonadotropin (gonadotropin), act on the ovary, and the follicle begins to develop and secretes estrogen. Estrogen causes the endometrium to proliferate and thicken, and the preparation for the fertilized egg begins.
Estrogen leads the endometrium to grow and thicken, and preparing the uterus to receive a fertilized egg. When the master follicle grows to about 20mm, the body judges that the follicle has developed sufficiently because follicle produce a lot of estrogen. After that, the concentration of LH rises rapidly (LH surge), the egg matures and ovulation occurs.
After ovulation, the follicle becomes a corpus luteum which produces progesterone and estrogen. Progesterone makes the thickened lining of the uterus more receptive to implantation for a fertilized egg. If the fertilized egg does not implant (i.e. there is no pregnancy), the corpus luteum reaches the end of its life after about 14 days and becomes a white body, so estrogen and progesterone level will decline. This causes the thickened endometrium to flake off and be expelled, and resulting in menstruation.
Function of gonadotropins
Gonadotropins are hormones secreted by the pituitary gland which include such as follicle stimulating hormone (FSH) and luteinizing hormone (LH). The female body is controlled by gonadotropin-releasing hormone (GnRH), which is secreted by the hypothalamus and it is responsible for the normal menstrual cycle, including follicle development, maturation and ovulation. When GnRH is secreted by the hypothalamus in the brain, the pituitary gland in the brain receives it and secretes FSH and LH.
Then, FSH and LH move to the ovaries through the bloodstream and these gonadotropins work for development and maturation of follicles. Hormone secretion is regulated by a feedback mechanism to ensure a normal menstrual cycle.
In the treatment of infertility, when FSH and LH levels are found to be insufficient, FSH and LH may be administered as a drug to stimulate follicle growth and maturation.
How female hormones work
Female hormones are the general term for estrogen and progesterone. Estrogen (E) is also called ‘follicle hormone’ because it is produced as the follicle develops. There are three types of estrogen: estrone (E1), estradiol (E2) and estriol (E3), but estradiol is the main estrogen that acts during sexual maturity. Estradiol is the most active out of these three estrogens and it is usually the main component of estrogen in blood which is measured by the test.
Progesterone (P, P4) is also called “luteal hormone” because it is mainly made in the corpus luteum. Progesterone prepares the fertilized egg to implant easily in the endometrium, and has the function of continuing pregnancy after implantation (pregnancy). In addition, since progesterone acts on the body temperature center of the brain that controls body temperature and also has the function of raising basal body temperature, the body temperature continues to be high (= high temperature period) while progesterone is secreted after ovulation, 0.3 ~ It rises by about 0.6 ° C.
If it is determined that estrogen or progesterone is insufficient during fertility treatment, it may be administered as a drug to promote the growth and thickening of the endometrium.