I am not sure if you need to write a paper on a disease process specifically, or if you have a little more freedom of choice in subjects. I have a potential suggestion. Often, asking a seemingly innocuous and esoteric question can lead you to profound answers and a great experience regarding research and writing the paper.
For example, for a recent assignment, I asked myself "why is Mercury a liquid at room temperature?" The journey to the answer was a wild ride and I was able to write a truly unique paper and complete a unique presentation. You could ask something on the lines of "how does the body use Oxygen or how is Carbon Dioxide produced?" I casually asked the CO2 question recently during a class on quantitative CO2 monitoring and was met with absolute silence and an opening to lecture on a subject that the students had apparently never really pondered or appreciated in any detail.
Asking a good question regardless of your choice of subjects will also help you develop a catchy and interesting introduction. A good introduction is crucial if you want people to continue reading your paper. Also, when you can make somebody view the physical world differently through your work, it can be a powerful experience for the person on the other side of your project.
Good luck.
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