The normal reproductive years of the female are characterized by monthly rhythmic changes in the rates of secretion of the female hormones and corresponding changes in the ovaries and sexual organs as well. This rhythmic pattern is called the female sexual cycle. The duration of the cycle averages 28 days.

Which hormones govern the female cycle

The female hormonal system consists of five hormones -

1. Luteinizing hormone releasing hormone (LHRH)

2. Follicle stimulating hormone (FSH): FSH stimulates the ovaries and growing follicles

3. Lutenizing hormone (LH): LH stimulates ovulation

4. Estrogen: It is responsible for regulating and sustaining female sexual development and reproductive function

5. Progesterone: It prepares endometrium for implantation

How are ovulation and menstruation defined

Ovulation is the end result of a complex series of events leading to the production and release of an egg. If that egg is fertilized and gets implanted in the lining of the uterus wall (endometrium) a pregnancy has commenced. If it is not fertilized then it is lost together with the endometrium as the menstrual blood flow at the beginning of your next period. These events are collectively known as the Menstrual Cycle and are controlled by a pea-sized structure called the pituitary gland, which is attached to the undersurface of the brain.

What happens during the menstrual cycle

1. At the beginning of a period, a hormone called Follicle Stimulating Hormone (FSH) is released from the pituitary gland. FSH stimulates a follicle on the surface of the ovary to grow. Contained within the follicle is the developing egg.

2. During the next two weeks the egg grows and matures, and as it does, so a female hormone called estrogen is produced in increasing quantities by the ovary. The estrogen in turn enters the bloodstream and feeds back to a part of the brain above the pituitary gland where it is recognized by special receptors. If enough estrogen has been produced, this feed back process decreases the production of FSH.

3. Rising estrogen levels also trigger the output of another hormone from the pituitary gland called Luteinizing Hormone (LH). This leads to the release of the mature egg from the follicle. The escape of the egg from the ovary is known as ovulation.

4. After ovulation, the empty follicle forms a structure called the corpus luteum, which produces the second female hormone called progesterone. The progesterone levels go up after ovulation, and maintain the endometrium in a state of readiness to receive a fertilized egg. If the fertilized egg does not implant itself the progesterone level falls and a period commences. The whole cycle now begins once more.