Infradian Rhythms

A type of biologival rhythm, with a frequency of less than once cycle in 24hrs, such as the menstrual cycle and seasonal affective disorder.

Endogenous system:

• An example of an infradian rhythm.
• Goverened by monthly changes in hormone levels, which regulate ovulation
• Average takes approx 28 days
• Rising levels of Oestrogen = cause ovary to develop an egg and release it = ovulation
• After ovulation = progerstrone levels increase = womb lining grows thicker in preparation for implantation of an embryo
• If pregnancy doesn't occur = egg abdorbed into body and womb lining comes away and leaves body through the menstrual flow

Exogenous factors: Stern and Mcclintock

• Synchronised as result of influence of female pheremones
• 29 women- history of irregular
• 9 = colect pheremones = pad under armpit for at least 8hrs
• Treated with alcohol and frozen
• Rubbed on upper lipof 20 
• 68% = changes = closer to 'odour donor' 

• Seasonal variation in humans
• Severely depressed during winter = winter blues
• Depressive disorder = persistent low mood/ general lack of interest
• Number of daylight hrs decreases = prolonged periods of daily darkness = affect on sleep/wake cycle
• During night = Pineal gland = secretes melatonin until dawn, when increase of light
• In winter = decrease of light in morning = secretion continues for longer
• Knock-on effect on seretonin = cause of depressive symptoms