Biological Rhythms - The Infradian Rhythm

Question 1

Infradian Rhythms

Answer 1

Infradian rhythms are biological cycles that last longer than 24 hours and can occur over a period of days, weeks, or seasons.

Question 2

Examples of Infradian Rhythms

Answer 2

1. The Menstrual Cycle
2. Seasonal Affective Disorder (SAD)

Question 3

1. The Menstrual Cycle

Answer 3

A monthly infradian rhythm is the female menstrual cycle, which is regulated by hormones that either promote ovulation or stimulate the uterus for fertilisation. Ovulation occurs roughly halfway through the cycle when oestrogen levels are at their highest, and usually last for 16-32 hours. After the ovulatory phase, the progesterone levels increase in preparation for the possible implantation of an embryo in the uterus. It is also important to note that although the usual menstrual cycle is around 28 days, there is considerable variation, with some women experiencing a short cycle of 23 days and others experiencing a longer cycle of up to 36 days.

Question 4

2. Seasonal Affective Disorder (SAD)

Answer 4

Another example of an infradian rhythm is related to the seasons. Research has found seasonal variation in mood, where some people become depressed in the winter, which is known as seasonal affective disorder (SAD). SAD is an infradian rhythm that is governed by a yearly cycle. Psychologists claim that melatonin, which is secreted by the pineal gland during the night, is partly responsible. The lack of light during the winter months results in a longer period of melatonin secretion, which is linked to the depressive symptoms.