Female Reproductive System - Hormonal Regulation

Human females follow a cyclical pattern called the menstrual cycle. The menstrual cycle is responsible to release the ovum in the same period as the uterus is most receptive to a fertilized egg.

The menstrual cycle usually takes 28 days to be completely, however it may very from women to women. The cycle is said to begin with menstruation and end with the start if the next menstrual period.

The menstrual cycle is said to be divided in two different, but interconnect, set of events. One takes place in the ovaries and its called the ovarian cycle, while the other takes place in the uterus, and its known as the uterine cycle.

The Ovarian Cycle

Each follicle contains a immature ovum inside. Many follicles degenerate during a girl's life time. In a single ovarian cycle, only on follicle will release a ovum, and then it will turn to a yellowish structure called corpus luteum, which will eventually degenerate. 

The ovarian cycle can be divided into two stages:

•  Follicular Stage: It all begins with a increase in the level of FSH in the body. This FSH will stimulate the development of one follicle. As the follicle matures, It releases some of the hormone called estrogen and some progesterone. As the level of estrogen increases, the production of FSH decreases and increases the production of GnRH which will stimulate the production of LH. The LH will trigger the release of ovum from the follicle (ovulation). 
• Luteal Stage: Once the ovum is released, the LH causes the follicle to develop into a corpus luteum. The corpus luteum will secrete some progesterone and estrogen, which will inhibit the production of LH. When the copus luteum degenerates, there is a decrease in the level of estrogen and progesterone. The low levels of these hormones will cause the production of FSH, which will trigger the cycle all over again. 

If the ovum is fertilized and implanted in the endometrium, the level of estrogen and progesterone will remain high in order of the hormone hCG, secreted by the embryo-supporting membrane. Progesterone will maintain the endometrium to support the developing fetus, while estrogen prevents other follicle to mature. 

The Uterine Cycle

If fertilization occurs, it take a few days until the zygote gets to the uterus. Thus, the uterus and endometrium must be prepared. There is a build up of tissues and blood vessels in the endometrium. If fertilization doesn't occur, the endometrium will disintegrates and menstrual cycle will begin all over again.

The uterine cycle start in the same day as the ovarian cycle. As a new follicle starts to be developed and the levels of estrogen and progesterone start to increase, which will cause the endometrium to begin thickening. If the corpus luteum degenerates and fertilization does not occur, the levels of estrogen and progesteron decreases causing the endometrium to break down.