Startin from puberty, a woman's ovaries and uterus perform a regular series of processes every 28 days.

Day 1-5: Blood and tissue from the uterus pass out of the vagina.

Day 6-14: The lining of the uterus thickens to receive an egg from the ovaries. In the ovaries, an egg starts to mature.

Day 14-28: around day14, an egg is released from an ovary. It travels down a fallopian tube to the uterus. If the eeg it's not fertilised, it leave the boddy with the blood and tissue. Then the cycle start again