Biological rhythms: Infradian and Ultradian rhythms

AO1

Infradian rhythm - the menstrual cycle: Governed by monthly changes in hormone levels that regulate ovulation. The cycle is the first day of a woman's period when her womb lining is shed to the day before her next period. In each cycle, oestrogen causes the gg to develop and be released (ovulation). After ovulation, progesterone thickens the womb lining to ready the woman for pregnancy. If this doesn't occur, the egg is absorbed by the body and the lining is shed (menstrual flow)

Research study on menstrual cycle: Evidence shows that the cycle can be influenced by exogenous zeitgebers. McClintock demonstrates synchronisation. 29 women who had irregular periods. Samples of pheromones were collected from 9 at different stages of their menstrual cycle by placing a cotton pad under their armpits for 8 hours which was frozen and then rubbed on the upper lip of the others. Pads from day one were applied to all 20 women, then day two etc. 68% of women faced changes in their cycle which brought them closer to the cycle of their odour donor.

Infradian rhythm - SAD: Symptoms are triggered during the winter when there is less sunlight. During the night the pineal gland secretes melotonin until it is light; however, due to less sunlight hours, this secretion process is longer which is thought to have a knock-on effect on serotonin which is linked…