Answer:
The Circulatory System and the Nervous system
Explanation:
I realize this question has already been answered, but if anyone wants more than one, I'm here to help!
The nervous system keeps the heart beating, as well as regulating other things, like letting the body know when the circulatory system is damaged. In return, the brain is kept alive with a lot of blood being pumped up there by the heart, despite gravity pushing it down.
Hope this helps!
