menstrual cycle

• stage one - menstruation starts

  the uterus lining breaks down for about four days
• stage two - the uterus lining build up again

  from day 4 - 14 into a thick spongy layer full of blood vessels ready to receive a fertilised egg
• stage 3 - an egg develops and is realsed

  from the ovary at day 14 this is called ovulation
• stage 4 - the wall is maintained

  for about day 14 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
• FSH

  produced in 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

  produces in the ovaries

  causes the lining of the uterus to grow

  stimulates the release of LH and inhibits the release of FSH
• LH

  produced by the pituitary gland

  stimulates the release of the egg at day 14
• 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