Toward the end of the menstrual (ovarian) cycle, retention of the thickened endometrium of the uterus depends upon the A. increase of gonadotropin production by the ovaries B. decrease of gonadotropin production by the ovaries C. egg being fertilized and the progesterone level decreasing D. egg being fertilized and the progesterone level remaining high
The correct answer and explanation is:
The correct answer is D. egg being fertilized and the progesterone level remaining high.
At the end of the menstrual cycle, if the egg has been fertilized, the corpus luteum (the structure formed from the follicle after ovulation) continues to produce high levels of progesterone. This hormone plays a crucial role in maintaining the thickened endometrium, which is necessary for implantation and supporting the early stages of pregnancy.
Progesterone works by stimulating the endometrial lining to become more glandular and vascular, creating an optimal environment for the fertilized egg to implant and develop. If pregnancy does not occur, the corpus luteum degenerates, leading to a decrease in progesterone levels. This drop triggers the shedding of the endometrial lining, resulting in menstruation.
In the event that the egg is fertilized, it releases a hormone called human chorionic gonadotropin (hCG), which signals the corpus luteum to continue producing progesterone. This is essential to prevent the shedding of the endometrium and ensure that the uterine environment remains suitable for the growing embryo. Therefore, the presence of a fertilized egg and the sustained high levels of progesterone are key factors in retaining the thickened endometrium during the early stages of pregnancy.
To summarize, the retention of the thickened endometrium depends on the combination of the egg being fertilized and progesterone levels remaining high, ensuring that the uterine environment is prepared for a successful pregnancy.