To keep cells alive, the body needs a constant supply of oxygen and nutrients.
Every thought, movement, and sensation is governed by the . This system is divided into two main parts: The Human Body
We live in a world full of bacteria, viruses, and toxins. The is the body's private security force. Using a combination of white blood cells, antibodies, and the lymphatic system, it identifies and neutralizes foreign invaders, often before we even realize we've been exposed to a threat. To keep cells alive, the body needs a
Attached to this frame is the . With over 600 muscles, this system allows for everything from the powerful stride of a sprinter to the microscopic adjustments of the eye. Muscles operate through a constant cycle of contraction and relaxation, fueled by the energy we consume. 2. The Command Center: The Nervous System The is the body's private security force