Proestrus in the cycle involves:

Proestrus in the cycle involves:

• A. The corpus luteum regresses and estradiol increases
• B. Ovulation occurs
• C. The uterus sheds
• D. The placenta forms

Answer: (A)

Proestrus features rising estrogen from maturing follicles as the cycle shifts from the luteal to the follicular phase, with the corpus luteum regressing and progesterone falling. This combination sets the stage for estrus: as the CL regresses, progesterone declines, and estradiol increases from the developing follicles. That is why the statement about the corpus luteum regressing and estradiol increasing best captures what happens in proestrus. The other events—ovulation occurs during estrus, the uterus shedding isn’t a proestrus feature in this cycle, and placenta formation is a pregnancy event—don’t occur in proestrus.

Proestrus features rising estrogen from maturing follicles as the cycle shifts from the luteal to the follicular phase, with the corpus luteum regressing and progesterone falling. This combination sets the stage for estrus: as the CL regresses, progesterone declines, and estradiol increases from the developing follicles. That is why the statement about the corpus luteum regressing and estradiol increasing best captures what happens in proestrus. The other events—ovulation occurs during estrus, the uterus shedding isn’t a proestrus feature in this cycle, and placenta formation is a pregnancy event—don’t occur in proestrus.