puberty and the menstrual cycle

• at puberty, your body starts to release sex hormones that trigger off secondary sexual characteristics - such as the development of facial hair in men and breasts in women and cause eggs to mature in women
• in men, the main reproductive hormone is testosterone - it's produced by the testes and stimulates sperm production
• in women, the main reproductive hormone is oestrogen - it's produced in the ovaries
• the menstrual cycle has 4 stages
• stage 1:

  day 1 - menstruation starts, the uterus lining breaks down for about four days
• stage 2:

  the uterus lining builds up again, from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg
• stage 3:

  an egg develops and is released from the ovary at day 14 - this is called ovulation
• stage 4:

  the wall is then maintained for about 14 days until day 28, if no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the whole cycle starts again
• the menstrual cycle is controlled by 4 hormones:

  • FSH (follicle-stimulating hormone)
  • oestrogen
  • LH (luteinising hormone)
  • progesterone
• FSH:

  • produced in the pituitary gland
  • causes an egg to mature in one of the ovaries, in a structure called a follicle
  • stimulates the ovaries to produce oestrogen
• oestrogen:

  • produced in the ovaries
  • causes the lining of the uterus to grow
  • stimulates the release of LH (which causes the release of an egg) and inhibits the release of FSH
• LH (luteinising hormone):

  • produced in the pituitary gland
  • stimulates the release of an egg at day 14 (ovulation)
• progesterone:

  • produced in the ovaries by the remains of the follicle after ovulation
  • maintains the lining of the uterus during the second half of the cycle, when the level of progesterone falls, the lining breaks down
  • inhibits the release of LH and FSH