My son is the same way. He LOVES anything related to the human body. To help satisfy his cravings for anatomy information, I have arranged interviews, which we called "play dates," with all the doctors and scientists I know...this has included reaching out to friends-of-friends. Suprisingly, these busy professionals have been more than eager to help my little guy. I think they find it amusing to discuss complex health issues with a 7 year old.
I have also hired a middle school science teacher to work with my son once a week. She selects study units based on his interests and then I work with him during the week on experiments and supplemental information.
When my son was first learning his body systems, we found brainpop.com to be a great resource. You can get a trial for free if you want to check it out. It has short educational videos on a ton of health related issues.
Once he mastered the functions of organs, etc., he quickly moved on to health problems, possible surgical solutions, etc. Since your son may follow the same path, I want to tell you about a book my son loves, it is called Atlas of Pathophysiology. When you've exhausted all the kid-related health books, this is a great transition to more sophisticated health material.
Good luck with your little science guy! I think you are very wise to help him follow his passion.
