INFRADIAN RHYTHMS

• What is an infradian rhythm?

  a biological rhythm that lasts longer than 24 hours
• example of an infradian rhythm

  menstrual cycle

  lasts about 28 days
• what happens in the menstrual phase?

  day 1-5

  uterus sheds inner lining, exits body as menstrual fluid

  low oestrogen levels cause low energy levels
• what happens in the follicular phase?

  day 6-13

  pituitary gland secretes FSH, stimulated egg cells to grow

  egg begins to mature and secretes oestrogen.

  rising oestrogen causes energy levels to increase
• what happens in the ovulation phase?

  day 14

  pituitary gland secretes LH, causes ovary to release egg into fallopian tube
• what happens in the luteal phase?

  day 15-28

  ovaries produce progesterone, maintains uterus lining

  if egg isn’t fertilised then progesterone levels fall until day 28. causes next cycle to begin
• strengths of research and EZs

  shows evolutionary value - may have been advantageous for women to menstruate together and become pregnant at same time

  Research - 29 women with irregular periods, rubbed pheromones sample on upper lIp and 68% cycle changed to be closer together
• limitations of research and EZs

  confounding variables, could be chance

  research uses small samples, relies on self reporting

  other studies failed to find any evidence of menstrual synchrony

  Validity of evolutionary belief has been questioned - too many females cycling together would produce competition of offspring