Fascinating way of teaching physiology, but very difficult and very linear. When I took the course, it wasn't available as self-paced, and the first exam came way too early. Nowadays, since it explores the connections between the organ systems, I would recommend one just to get started and keep going. Eventually it will start to make more sense, and then you can refresh the older material and take the exams. Some people in the forums have also recommended watching basic videos on youtube first.