Don't let the material overwhelm you. The human body is a very logically put-together, all be it complicated, machine. If you are having trouble learning a system, google it. You will find web sites that give short, lay-person explanations that help to sort out the medical language. Once you see the big picture, you can start focusing on the finer points. For example, the heart is a pump...just that simple. Learn the flow of blood through the body...it goes in a perfectly logical sequence. Once you figure that out, then you can start to look at what happens when the heart doesn't work right. Sometimes, if you are in the middle of a class and completely lost, go back to the fundamental working of the organ and then work your way back to what was being covered in the lecture. I had to do that on MANY OCCASIONS, even though I had a BS in Biology and was making straight A's. I'd be totally lost. Hang in there, study, and think logically. Once you get the logic down, then you can start mastering the critical thinking. I just took and passed my NCLEX, so trust me when I tell you that that is the most important skill you have to master.
(Need to figure out how to change my online name. Just got a full time job as an LPN, so I'm not just a new student any longer)