What is a menstrual cycle and why do girls have them?
What is a menstrual cycle?
A menstrual cycle is a series of natural changes in a woman's reproductive system that makes pregnancy possible. The cycle is controlled by the pituitary and hypothalamus glands in the brain and the ovaries.
The menstrual cycle has four phases:
1. The follicular phase begins on the first day of menstruation and ends when ovulation occurs. During this phase, the ovaries produce estrogen, which thickens the lining of the uterus (endometrium).
2. Ovulation occurs when a mature egg is released from one of the ovaries. This usually happens around day 14 of the menstrual cycle, but it can vary from woman to woman.
3. The luteal phase begins after ovulation and ends when menstruation begins. During this phase, the corpus luteum (a small gland that forms on the ovary after ovulation) produces progesterone, which helps to maintain the lining of the uterus.
4. Menstruation begins when the lining of the uterus sheds and is expelled from the body through the vagina. This usually lasts for 3-5 days, but it can vary from woman to woman.
Why do girls have menstrual cycles?
Menstrual cycles are part of the normal reproductive process. They prepare the body for pregnancy each month. If pregnancy does not occur, the lining of the uterus is shed during menstruation.
Menstrual cycles also help to regulate a woman's hormones. Estrogen and progesterone are important hormones that play a role in many different bodily functions, including:
* Reproduction
* Metabolism
* Mood
* Appetite
* Sleep
The menstrual cycle helps to ensure that these hormones are produced in the right amounts at the right times.
When do girls start having menstrual cycles?
Girls usually start having menstrual cycles between the ages of 12 and 15, but it can vary from girl to girl. Some girls may start as early as 10, while others may not start until they are 16 or older.
The first few menstrual cycles can be irregular, but they usually become more regular over time.