Infradian rhythm - the menstrual cycle

• Circadian rhythm


  Cycle of sleeping and waking regulated by an internal body clock
• Ultradian rhythm


  Rhythm that occurs more frequently than once per day
• Infradian rhythm


  Rhythm that occurs less frequently than once per day
• Menstrual cycle


  Female biological rhythm of fertility, typically 28 days
• Menstrual cycles can range from 24 to 35 days
• Menstrual cycle


  • Releasing the egg
  • Thickening of the womb lining
  • Loosening of the womb lining during menstruation
• Hormones


  Estrogen and progesterone act as endogenous pacemakers regulating the menstrual cycle
• Research has shown women's menstrual cycles can synchronize when living together
• Proposed reasons for menstrual cycle synchronization include sharing pheromones and evolutionary advantages
• There is debate and conflicting evidence around the validity of menstrual cycle synchronization
• The word 'menstrual' has roots in the Greek word for moon, but there is no link between menstrual cycles and moon phases