Monthly Menstrual Cycle
From the first period to menopause
Menstruation generally begins between the ages of 10 and 13 (average age 12). It may take a year or two for girls to get their periods back on track. Then, menstruation will occur once a month until menopause, unless a woman becomes pregnant. The average time for menstruation to stop is around age 51.
Timing of the Monthly Menstrual Cycle
The first day of a monthly cycle is the first day of menstruation, or the first day that bleeding begins. The next cycle begins at the beginning of the next menstrual period.
It may seem strange, but not all women menstruate once a month. The average length of a cycle is 28 days, but since this length can vary between 21 and 35 days, those with shorter cycles menstruate more than once a month on average in a year, and conversely, those with longer cycles menstruate less than once a month on average in a year.
Reproductive organs
It is very useful to know how the reproductive organs work and how they work together. The reproductive system includes the following organs:
- Two ovaries: The place where eggs are stored and released. A human egg is very small, when fully developed it will be about 120 microns or micrometers in size. This is about the diameter of a hair. The ovaries also secrete hormones.
- Uterus: The place where a fertilized egg implants and is carried there until birth.
- Fallopian tubes: These two very thin tubes carry eggs from the ovaries to the uterus.
- Cervix: The lowest part of the uterus that connects the uterus to the vagina.
- Vagina: A flexible passageway between the uterus and the outside of the body through which menstrual blood exits and through which the baby is born. The vagina is inside the body. The part of the body that is on the outside and visible is called the vulva.
How Hormones Control the Menstrual Cycle
Each month, your reproductive system goes through a specific pattern of changes that are controlled by hormones, especially estrogen and progesterone. The rise in these hormones causes an egg to grow and be released, a phase called ovulation. After ovulation, the hormones affect the lining of the uterus and thicken it to prepare the body for pregnancy. Each month, an egg is released from the ovaries and travels down the fallopian tubes. If pregnancy does not occur, the released egg is expelled from the body along with menstrual blood. Estrogen and progesterone levels drop, and the lining of the uterus breaks down and is shed. This phase is actually the same as menstrual bleeding. The period between the release of the egg and the start of menstruation lasts about two weeks.
