Biological rhythms: Infradian and ultradian rhythms:

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  • Infradian rhythms:
  • AO1:
  • The himan female mentrual cycle is about 28 days (i.e. less than one cycle in 24 hours - infra deim meaning 'below' a day). Rising levels od oestrogen cause the ovary to develop and release an egg (ovulation). Then progesterone helps the womb lining to thicken, readying the body for pregnancy. If the pregnancy doesn't occur, the egg is absorbed into the body and the womb lining comes away and leaves the body (mentrual flow). 
  • Study:
  • Stern and McClintock studied 29 women with irregular periods. Phermones were taken from some at different stages of their cycles, via a cotton pad under their armpits. These pads were cleaned eith alcohol and later rubbed on the upper lips of the other participants. 68% of women experienced changes to their cycle which brought them closer to the cycle of the 'odour donor'. 
  • Seasonal affective disorder (SAD) is a depressive disorder (low mood, lack of activity) with a seasonal pattern. Often called the 'winter blues' because the symptoms are triggered during the winter months when the number of daylight hours becomes shorter. SAD is an infradianrhythm called a circannual (yearly) cycle. 
  • During the night, the pineal gland secretes melatonin until dawn when there is an increase in light. During winter, the lack of light in the morning means secretion goes on for longer. This has a knock-on effect on the production of serotonin in the brain (low serotonin is linked to depressive symptoms). Therefore saying that SAD could be caused by the hormone melatonin. 
  • Ultradian rhythms:
  • Stages of sleep are an intradian rhythm. Sleep patterm occurs in 90-minute periods (i.e. more than one cylce in 24 hours - ultra deim meaning 'beyond' a…


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