Final answer:
The innermost layer of the endometrium that sheds during menstruation is known as the stratum functionalis.
Step-by-step explanation:
The innermost layer of the endometrium that is shed during each menstrual period is the stratum functionalis. The endometrium consists of two layers: the stratum basalis and the stratum functionalis. The stratum functionalis is the layer that grows and thickens in response to increased levels of estrogen and progesterone, providing a site for potential implantation of a fertilized egg. If no fertilization occurs, it is this layer that sheds during the menses phase of the menstrual cycle, leading to menstruation.