Final answer:
During menstruation, the layer of the uterine wall that is shed is the functional layer of endometrium, which responds to hormonal changes and thickens in preparation for a potential pregnancy.
Step-by-step explanation:
The layer of the uterine wall that is sloughed off during menstruation is the functional layer of endometrium. The innermost layer of the uterus, the endometrium, is composed of two layers: the basal layer, which does not shed during menstruation, and the functional layer. The functional layer grows and thickens in response to hormones and is the portion that is shed if fertilization of an egg does not occur, resulting in menstruation.