Definition

Menstruation is the vaginal bleeding that occurs in adolescent girls and women as a result of hormonal changes. It normally happens in a predictable pattern, once a month.

Description

Menstruation is part of the menstrual cycle, which helps a woman's body prepare for the possibility of pregnancy each month. The parts of the body involved in the menstrual cycle include the uterus and cervix, the ovaries, fallopian tubes, the brain and pituitary gland, and the vagina. Certain body chemicals known as hormones rise and fall during the month, causing the menstrual cycle to occur.

In the first half of the menstrual cycle, estrogen levels rise, causing the lining of the uterus to grow and thicken. This lining is called the endometrium. The two small, grape-shaped organs inside...