Infradian Rhythms

• Infradian rhythms 


  -these are cyclical changes in the biological processes that take longer than 24 hours to complete one full cycle.

  -e.g. female menstrual cycle and seasonal affective disorder

  -Peak and trough of hormone levels: LH, FSH, oestrogen and progesterone.

  -Those hormones stimulate changes in the reproductive anatomy of females in preparation for a fertilised egg to embed and develop into a foetus.
• Infradian rhythms - menstrual stages

  
  

  -Menstrual phase - pregnancy has not occurred. Oestrogen and progesterone levels decrease causing lining to shed (period).

  -Follicular phase - hormone FSH rises causing eggs contained inside the follicle to ripen. The developing egg causes release of oestrogen causing the uterus lining to thicken.
• Infradian rhythms - menstrual stages

  -Ovulation phase - rise in LH causes the egg to be released and travel down the fallopian tube.

  -Luteal phase - rise in progesterone and oestrogen causes womb lining to thicken. These hormones decrease if fertilisation doesn't occur and female enters menstrual phase again. Cycle repeats.
• Research support - Armpit pheromones and McClintock effect

  -McClintock noticed a synchronisation of menstrual cycles amongst women living in close proximity.

  -They followed 29 women who had a history of irregular menstrual cycles. Sweat was collected from 9 women then sterilised and dabbed onto the upper lip of the other 20 women

  -68% of recipients of the sweat donation had responded to the pheromones as their menstrual cycle had synched.

  -However, there are a number of co-founding variables which may influenced menstrual synchrony like stress, diet exercise and health conditions.