Two awesome resources that I couldn't pin! KidsHealth.org
is an awesome website for studying the human body. It has all sorts of great information written for children and teens. It's straightforward and written in student friendly language. There are some fun animations and my favorite part, you can chose to listen to the entire article. If you click on "Body Basics Library" then it will give you drop downs on all sorts of different systems.
One of my other favorite body resources (without the choice to pin!) is Exploring Science
. This website is awesome on it's own but it has some great research on different body systems. What I also love is that it archives other related websites (kid friendly) as well as asks you to be an explorer and check out other cool follow ups to what you've just learned about.