Which system is the stomach in?

Inside each lung, there are tubes called bronchi. These branch into even smaller tubes much like branches on a tree. What are at the ends of the tubes?

What blood vessels take blood away from the heart after oxygen is added?

Which systems defends body against infection

The Pituitary gland is made of two parts. Which part makes 2 hormones?

Which system secretes hormones.

Another name of the back of an organism?

The part of the nerve cell that receives messages. 

Which of the four major tissues covers body surfaces and lines the body cavities?

As the blood returns back to the lungs, what is removed from the blood?