Which phase marks the luteal phase of the estrous cycle?

Which phase marks the luteal phase of the estrous cycle?

• A. Proestrus
• B. Estrus
• C. Metestrus and Diestrus
• D. Ovulation

Answer: (C)

The luteal phase is the period after ovulation when the corpus luteum forms and secretes progesterone to prepare and maintain the uterus for possible pregnancy. In the estrous cycle, this occurs during metestrus (the transition as the corpus luteum starts forming) and diestrus (when the corpus luteum is fully active and progesterone is high). So the luteal phase is best described by metestrus and diestrus. Proestrus is the follicular, estrogen-raising phase before heat; estrus is the heat/ovulation window; and ovulation is the release of the oocyte itself. These are not luteal phases because they precede or coincide with follicular activity rather than with the progesterone-dominated luteal activity.

The luteal phase is the period after ovulation when the corpus luteum forms and secretes progesterone to prepare and maintain the uterus for possible pregnancy. In the estrous cycle, this occurs during metestrus (the transition as the corpus luteum starts forming) and diestrus (when the corpus luteum is fully active and progesterone is high). So the luteal phase is best described by metestrus and diestrus.

Proestrus is the follicular, estrogen-raising phase before heat; estrus is the heat/ovulation window; and ovulation is the release of the oocyte itself. These are not luteal phases because they precede or coincide with follicular activity rather than with the progesterone-dominated luteal activity.