Why does menstrual flow comes once a month?

Menstrual flow, also known as menstruation or a period, occurs as part of a woman's monthly menstrual cycle. The menstrual cycle is a complex biological process that involves hormonal changes and the preparation of the uterus for possible pregnancy. The average menstrual cycle lasts about 28 days, but it can vary from woman to woman.

Here's why menstrual flow occurs once a month:

1. Menstrual Cycle Phases: The menstrual cycle consists of four main phases: the follicular phase, ovulation, the luteal phase, and menstruation. During the follicular phase, the body prepares for ovulation, and the hormone estrogen thickens the lining of the uterus (endometrium) in preparation for a potential pregnancy.

2. Ovulation: Around day 14 of a 28-day cycle, ovulation occurs when a mature egg is released from one of the ovaries. If the egg is not fertilized by sperm during this time, it disintegrates.

3. Luteal Phase: After ovulation, the corpus luteum (a structure formed from the ruptured follicle) produces the hormone progesterone, which helps maintain the thickened uterine lining. If pregnancy does not occur, the corpus luteum begins to break down, leading to a decrease in progesterone levels.

4. Menstrual Phase: When progesterone levels drop, the thickened lining of the uterus is no longer supported, and it sheds. The shedding of this tissue and blood through the vagina is what causes menstrual flow. Menstruation typically lasts for about 3 to 7 days.

5. Hormonal Regulation: The menstrual cycle is regulated by various hormones, including estrogen, progesterone, and gonadotropin-releasing hormone (GnRH). These hormones work together to control the growth and shedding of the uterine lining, as well as the release of an egg during ovulation.

So, menstrual flow occurs once a month because it's a part of the natural menstrual cycle, which involves hormonal changes and the preparation of the uterus for possible pregnancy each month. When pregnancy doesn't occur, the uterine lining is shed during menstruation, and the cycle starts again.