Menstrual cycle

Artwork showing the stages and relationship between events during a female menstrual cycle. The central disk reads clockwise from the top, starting at day 1 of the cycle. The levels of each of the four main hormones are represented by the four coloured discs. Red = follicle stimulating hormone, green = oestrogen, yellow = lutinizing hormone and blue = progesterone. The intensity of each colour denotes the concentration of the hormone in the blood. The five surrounding illustrations show the corresponding changes in the ovary and the lining of the uterus (endometrium) as it prepares for potential pregnancy. After ovulation, if fertilisation does not occur, the corpus luteum demises after about 10 days and the uterine lining sheds, ready for the next cycle.