Question

In the absence of the implantation of a fertilized embryo, the menstrual phase of the uterine cycle is initiated by the degeneration of the ________.

Answer 1

The menstrual phase is triggered by the degeneration of the corpus luteum, which leads to lower levels of estrogen and progesterone and initiates the shedding of the endometrial lining.

Step-by-step explanation:

In the absence of the implantation of a fertilized embryo, the menstrual phase of the uterine cycle is initiated by the degeneration of the corpus luteum. The menstrual cycle starts when the corpus luteum degenerates, leading to a decrease in the levels of estrogen and progesterone.

This decrease in hormones, particularly progesterone, results in the degeneration of the endometrium, which initiates the menstrual phase. The endometrium can no longer be maintained, thus the shedding of the endometrial lining occurs as the menstruation part of the cycle.

If no fertilized egg is implanted into the uterus, the corpus luteum degenerates and the levels of estrogen and progesterone decrease. The endometrium begins to degenerate as the progesterone levels drop, initiating the next menstrual cycle. The decrease in progesterone also allows the hypothalamus to send GnRH to the anterior pituitary, releasing FSH and LH and starting the cycles again.