The menstrual cycle

Animal coordination, control and homeostasis · The menstrual cycle and fertility control · note 1 of 5

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The menstrual cycleSpec 7.4

The menstrual cycle is a series of changes in a woman that repeats about every 28 days. Each cycle, an egg is released from an ovary and the lining of the uterus is prepared in case the egg is fertilised.

Stages of the menstrual cycle (days are approximate)
Stage	Days	What happens
Menstruation	1 to 5	The lining of the uterus breaks down and is lost through the vagina with blood
Repair	5 to 14	The uterus lining is repaired and thickens again
Ovulation	Around 14	An egg is released from an ovary
Maintenance	14 to 28	The lining stays thick, ready for a fertilised egg. If there is no pregnancy it breaks down and the cycle starts again

The roles of two hormones

Oestrogen is made in the ovaries. It causes the repair and growth of the uterus lining.
Progesterone is made in the ovaries. It maintains the uterus lining.

A 28-day timeline divided into menstruation (days 1 to 5), repair (days 5 to 14) and maintenance (days 14 to 28), with ovulation at day 14 and a strip below showing the uterus lining thin after menstruation, thickening during repair and staying thick during maintenance. — The stages of the menstrual cycle and how the thickness of the **uterus lining** changes.