Infradian Cycles

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Infradian Rhythms

Infradian rhythms have a periodicity of more than one day, e.g. the female menstrual cycle and hibernation.

Menstrual cycle

The human menstrual cycle is controlled by hormones. The human menstrual cycle (also called the oestrous cycle) lasts about 28 days. The menstrual cycle involves:

A follicle (an egg and its surrounding protective cells) developing in the ovary.

Ovulation – an egg being released.

The uterus lining becoming thicker so that a fertilised egg can implant.

A structure called the corpus luteum developing from the remains of the follicle.

If there’s no fertilisation the uterus lining breaks down and leaves the body through the vagina. This is known as menstruation, which marks the end of one cycle and the start of another.

1.       The menstrual cycle begins when the uterus lining is shed, along with some blood (days 1-5).

2.       From day 1, the pituitary gland releases FSH into the blood which stimulates follicles in the ovary


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