Hormones in reproduction and the menstrual cycle

During puberty, reproductive hormones cause secondary sex characteristics to develop, e.g. pubic hair.
Oestrogen is the main female reproductive hormone, which is produced in the ovaries. At puberty, eggs begin to mature, and one is released approximately every 28 days (ovulation).
Testosterone is the main male reproductive hormone, produced by testes, stimulating sperm production.
The menstrual cycle is around 28 days long and requires oestrogen and progesterone from the ovaries and follicle-stimulating hormone (FSH) and luteinising hormone (LH) produced by the pituitary gland.
Several hormones interact in the menstrual cycle to control it:
- FSH causes maturation of an egg in the ovary and stimulates ovaries to produce oestrogen.
- Oestrogen thickens the uterus lining in preparation for a fertilised ovum, after menstruation. High oestrogen concentration inhibits the release of FSH and stimulates the release of LH.
- LH stimulates the release of the egg around day 14.
- Progesterone maintains the thick uterus lining if a fertilised ovum embeds in it, preventing menstruation. High progesterone concentration inhibits release of FSH and LH.
- If no fertilised ovum embeds in the uterus lining, less progesterone is produced, and the uterus lining shreds (menstruation). This starts on day 1, lasts approximately 5 days, and marks the start of the cycle.

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