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Menstrual Cycle

A women’s menstrual cycle explained.

Menstruation is a woman’s monthly “period” when the vagina discharges blood and mucus. This happens as part of the 28-day menstrual cycle of egg production controlled by a hormone feedback system run by the hypothalamus and pituitary gland in the brain.

From day one in the cycle, the follicle stimulating hormone (FSH) helps a new egg form in an egg follicle. From day four, the follicle produces oestrogen, a hormone that promotes growth of the womb and breasts, and encourages the release of luteinising hormone (LH) that blocks FSH output. From day 12, LH bursts the follicle, releasing an egg (ovum) and transforms the follicle into a corpus luteum, yielding oestrogen and progesterone.

From day 14, progesterone prepares the uterus (womb) wall to receive a fertilised egg. If fertilisation fails to occur, the corpus luteum shrinks, LH, oestrogen, and progesterone output fall, the uterus lining breaks up, and its bloody fragments escape in the monthly menstrual bleeding. Essentially, every month a menstruating woman’s body prepares for a pregnancy that may, or may not occur.

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