What term defines the cyclic period of sexual receptivity in mammals?

• A. Diestrus
• B. Proestrus
• C. Estrus
• D. Anestrus

Answer: (C)

Estrus is the phase when a female mammal is sexually receptive to mating. It follows the period when the reproductive tract is being prepared and estrogen levels are rising, and it often coincides with ovulation in many species. Behaviorally, females in estrus typically show mating signals and receptivity, signaling to males that they are fertile. Hormone-wise, rising estrogen sets the stage for ovulation, and in many animals the LH surge that triggers ovulation occurs during this time. After estrus, the cycle moves into diestrus, a luteal phase dominated by progesterone as the corpus luteum forms. Anestrus is a quiet period with no reproductive cycling. In humans, the term estrus isn’t used; the analogous cycle is the menstrual cycle.