Agreed. It can vary from institution to institution, and from student to student. I found anatomy easy while others found it very difficult, and vice versa for physics. It's the same with any topic. Some people have the kind of brain which takes to some material. Have you taken physiology or another biology class with an endocrine section in it? That could tell you something of your particular affinity for the topic. I know that endocrinology in particular is very puzzle-like - here are the signs, where does the problem originate? It requires some deductive reasoning.