menstrual cycle

• when are sex hormones produced?

  at puberty
• what do sex hormones do?

  they trigger secondary sexual characteristics and maturing of eggs in women
• secondary sexual characteristics


  physical signs of sexual maturation that do not directly involve sex organs
• what are males' main reproductive hormone?

  testosterone produced by the testes and stimulates sperm production
• what are females' main productive hormone?

  oestrogen produced by the ovaries
• menstrual cycle stages


  1) day 1, menstruation starts - lining breaks down for about 4 days

  2) uterus lining build up, from day 4 to 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg

  3) an egg develops and is released from the ovary at day 14 - this is called ovulation

  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

  ...next cycle starts again
• what happens when menstruation starts?

  the uterus lining breaks (day 1 to 4)
• why does the uterus lining build up again?

  so it is ready to receive a fertilised egg (day 4 to 14)
• what is ovulation?


  the development and release of an egg from the ovary (day 14)
• how long is the uterus' lining maintained for?

  for 14 days until day 28
• why does the lining of the uterus wall break down?

  if no fertilised eggs lands on the wall by day 28
• what is the menstrual cycle controlled by?

  4 hormones: FSH, oestrogen, LH and progesterone
• FSH (follicle stimulating hormone)

  - 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

  - inhibits the release of FSH
• LH (luteinizing hormone)


  - produced in by 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 release of LH and FSH