MEDtropolis is a very interesting site that I found a few years ago. The site tagline is "A webspace built for the latest health information that will educate and entertain kids and adults alike."
The site has information about different medical topics, such as bariatric surgery, diabetes and more.
But, the really cool part of the site is the Virtual Body. The Virtual Body is literally a virtual tour of the human body. You can explore the Brain, Skeleton, Heart, and Digestive tract. Each part can be explored and manipulated and some sections even have narrated tours.
In some parts, as you move your mouse over certain parts of the system, notes and information will come up on the screen. I think that it would be suitable for grades 7-12.
I found it easy to use and a great resource for students.