Infradian rhythms

• What are infradian rhythms?

  • Biological rhythms with a frequency of less than one in 24 hours
  • E.g. menstrual cycle
• Menstrual cycle

  • Time between first day of period and day before next
  • Regulated by hormones - oestrogen and progesterone
  • Typical cycle is 28 days (can range from 24-35)
  • Increase in oestrogen during first half - triggers ovary to develop and release egg
  • Increase in progesterone during second half, thickening of womb lining preparing for implantation of egg
  • If not pregnant, egg is absorbed, progesterone and oestrogen levels drop and lining sheds