The menstrual cycle and pregnancy

• what are the 4 stages of menstrual cycle?

  • Day 1 - menstruation starts - uterus lining breaks down for about four days
  • Stage 2 - uterus lining builds up again - from day 4-14 into a thick spongy layer full of blood vessels ready to receive a fertilised egg
  • Stage 3- egg develops and is released from ovary at day 14 - ovulation
  • Stage 4 - wall is maintained for about 14 days until day 28 - no fertilised egg landed on uterus wall by day 28 - spongy lining starts to break down and whole cycle starts again
• what 4 hormones control the menstrual cycle?

  • FSH - produced in pituitary gland - causes egg to mature into ovary in structure called a follicle - stimulates ovaries to produce oestrogen - oestrogen then inhibits release of FSH
  • oestrogen - produced in ovaries - cause lining of uterus to grow - stimulates release of LH
  • LH - produced in pituitary gland - stimulates the release of an egg at day 14 - ovulation
  • progesterone - produced in ovaries by remains of follicle after ovulation - maintain lining of uterus during 2nd half of cycle - level of progesterone falls - lining breaks down - inhibits release of LH and FSH
• how does the embryo develop during pregnancy?

  • once ovum has been feritilised - develops into embryo and implants in uterus - later stages of pregnancy embryo is a fetus
  • once embryo is implanted - placenta develops - lets blood of embryo and mother get very close to allow exchange of food, oxygen and waste
  • the amnion membrane forms - surrounds embryo and is full of amniotic fluid - amniotic fluid protects embryo against knock and bumps