menstrual cycle

n. The reproductive cycle of female anthropoid primates, including humans. Levels of hormones from the pituitary (luteinizing hormone [LH] and follicle-stimulating hormone [FSH]) and ovaries (estrogen and progesterone) rise and fall in feedback loops over the course of approximately a month. This controls the timing of fertility. Unlike mammalian females with the more common estrous cycle, females with menstrual cycles can copulate at any point during the cycle. Thus sexual receptivity is not bound to hormone levels or fertility. The cycle has effects on sexual desire and on a range of other behaviors, including some cognitive tasks, but these effects are very subtle.

- JMJ