Anatomy and Physiology II Practice Test 2025 - Free Anatomy Practice Questions and Study Guide

The phase of the reproductive cycle that begins when the uterine wall starts to thicken is the proliferative phase. This phase follows menstruation and is characterized by the rebuilding and thickening of the endometrial lining in response to rising levels of estrogen released from the developing follicles in the ovaries. As the follicles mature, they release more estrogen, stimulating the proliferation of the uterine lining to prepare for a potential implantation of a fertilized egg. This thickening occurs as the endometrial cells divide and increase in number, making the uterine environment more suitable for possible pregnancy.

In this context, the secretory phase, which occurs after the proliferative phase, involves further modifications of the endometrium, primarily influenced by progesterone, to prepare the uterus for implantation. The follicular phase pertains to the growth of the ovarian follicles before ovulation and does not directly influence the thickening of the uterine wall. The menstrual phase marks the shedding of the endometrial lining when pregnancy has not occurred, rather than any thickening process.