Contraceptive pill. Artwork of the action of an oral contraceptive (pill, white, upper left) on the female reproductive system. The pill's hormones target the hypothalamus (orange) in the brain (top centre), stopping the pituitary gland (red) from producing sex hormones. The monthly release (ovulation) of an egg from the ovaries (light pink, lower left and right) is prevented. In case an egg (red ball, upper left) is released, the uterus lining (endometrium, red and pink, far left) is altered, preventing implantation, and the mucus (white, at right and lower centre) in the uterine neck is thickened, obstructing the passage of sperm (green and purple, far right).