Because it is easy to identify without ambiguity, the first day of the uterine cycle is the day on which the _____ of the endometrium begins to be shed, emerging from the vagina together with blood in a process called _____.

3000+ review questions on anatomy and physiology. 

Anatomy refers to the internal and external structures of the body and their physical relationships, whereas physiology refers to the study of the functions of those structures.