The menstrual cycle of a normal human female lasts approximately how many days?

1. The reproductive tissue of the uterus is prepared monthly to receive a fertilised egg. 2. When fertilisation does not occur, the lining and unfertilised egg shed as menstrual flow. 3. The full cycle from one period to the next is about 28 days on average. _Source: syllabus Science, Ch 7 "How do Organisms Reproduce", §7.3.3_