estrous cycle

The estrous cycle is the reproductive cycle in female mammals, excluding higher primates, during which they are receptive to mating. This period, often called "heat," typically coincides with ovulation. The cycle is regulated by hormones from the pituitary gland and ovaries.

During the cycle, the uterine lining thickens in preparation for a potential fertilized egg. If pregnancy does not occur, the uterine lining is reabsorbed or shed, depending on the species. Some animals, like dogs, have one estrous cycle per breeding season (monestrous), while others, like ground squirrels, may have multiple cycles if not impregnated (polyestrous). Males can detect females in heat through pheromones, and females may exhibit behavioral changes and physical swelling in their genital areas. The menstrual cycle in humans and other primates is a variation of the estrous cycle, differing in how the uterine lining is shed.123