Infradian Rhythms AO1

• Infradian rhythms


  Rhythms with a duration of over 24 hours
• Menstrual cycle


  1. Oestrogen rises

  2. Ovulation happens

  3. Progesterone thickens womb

  4. If no pregnancy, womb lining is shed
• Seasonal affective disorder (SAD)


  Yearly cycle with seasonal variation in mood
• Melatonin


  Hormone secreted by the pineal gland
• Lack of light in winter

  Melatonin is secreted for longer
• Melatonin secreted for longer


  Affects production of serotonin, which is linked to depression
• Exogenous zeitgebers


  External cues that can affect biological rhythms (e.g. light for SAD, pheromones for menstrual cycle)