menstrual cycle

• important role of endocrine system is in human reproduction
• during puberty - reproductive hormones cause secondary sexual characteristics to develop e.g pubic hair
• testes produce testosterone - stimulates testes to produce sperm
• ovaries produce hormone oestrogen
• once puberty begins - eggs in ovaries start to mature
• egg is released every 28 days (ovulation)
• release of egg is part of menstrual cycle
• in preparation for ovulation - uterus lining becomes thick and spongy
• if sperm is present - egg can be fertilised - implants into uterus wall - develops into a baby
• if egg doesn't get fertilised - both egg and uterus lining are released (period)
• follicle stimulating hormone (fsh)

  causes egg to mature in ovary
• luteinising hormone (lh)

  causes egg to be released (ovulation)
• oestrogen and progesterone

  produced in ovary, involved in maintaining uterus lining incase egg is fertilised and implants
• fsh released by pituitary gland - travels in blood to ovaries - makes oestrogen at same time - causes lining of uterus to become thick - stops pituitary gland releasing fsh - instead releases lh - triggers ovulation - once ovary releases egg, produces progesterone - stops pituitary gland releasing fsh and lh - prevents more eggs maturing and being released - keeps lining of uterus thick incase fertilised egg implants
• if fertilisation doesn't take place - level of progesterone falls - uterus lining and egg released - period
• level of fsh rises - triggers ovaries to release oestrogen
• level of oestrogen increases - inhibits production of fsh - level of fsh falls
• oestrogen triggers release of lh - lh rises to peak around day 14
• lh triggers ovulation - ovary releases progesterone - progesterone level rises - fertilisation doesn't happen - progesterone level falls - period