Menstruation is the periodic discharge of blood, mucus, and tissue from the uterus due to the change of the uterine lining (endometrium).
From the pubertal stage, (which begins around age 11-12) first menstruation (menarche) cycle can be irregular for 2-3 years because of unbalanced hormonal secretion with or without ovulation.
It then becomes more regular during the mid- to late teen years.
Menstruation then continues throughout a women's life until she reaches menopause.
The mechanism that regulates the sloughing of the uterine lining is controlled by changing levels of female hormones. It begins every month when follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are released from the pituitary gland, which is located at the base of the brain. Once FSH and LH are released, they influence the ovaries.
During each cycle, FSH and LH cause one follicle to grow, and normally one egg is released from the follicle for possible fertilization. After this process, the follicle begins to produce estrogen and progesterone. Estrogen levels peak during the first half of the cycle as the newly released egg is maturing. Progesterone levels peak after midcycle when ovulation has occurred. Ovulation refers to the production of a mature egg.
Estrogen and progesterone stimulate the lining of the uterus. During the first 2 weeks following menstruation, estrogen causes the uterine lining to grow gradually and the lining thickens by increasing the number of blood vessels.
By midcycle, the inner lining of the uterus (endometrium) has increased 3 times in thickness and has a greatly increased blood supply.
After midcycle, usually 14 days before menstruation, the egg is received by the fallopian tube.
If the egg is fertilized, a large ovarian follicle, now called a corpus luteum cyst, secretes progesterone.
If fertilization does not occur, the follicle begins to deteriorate and the progesterone levels decrease. The abrupt decrease in progesterone levels causes the lining of the uterus break down and menstruation begins.
Bloody uterine discharge exits the vagina.
Normal menstrual cycle: 21-25 days
Menstruation period: 2-7 days
Normal menstrual blood, 25-80 cc