What is menstrual cycle? Describe it in brief.

The repetitive changes that occur in the female reproductive system every 28 to 30 days from puberty to menopause are called the menstrual cycle.

It is controlled by four hormones: FSH, LH, estrogen and progesterone.

1. Under FSH from the pituitary, one follicle in the ovary develops along with its oocyte. The follicle secretes estrogen.
2. Estrogen makes the endometrium of the uterus grow (or regenerate).
3. Under LH, the fully grown follicle bursts and releases the oocyte. This is ovulation.
4. The remaining part of the follicle becomes the corpus luteum, which secretes progesterone (and estrogen). Endometrial glands become active and the uterus is ready for implantation.
5. If the oocyte is not fertilized within about 24 hours, the corpus luteum becomes inactive (corpus albicans), estrogen and progesterone secretion stops and the endometrium degenerates. Its tissues and the unfertilized ovum are discharged through the vagina with bleeding for about five days. This is menstruation.

The cycle repeats every month unless an embryo is implanted; then it stops until after childbirth and breast feeding.