3. The Life Support Loop: Circulatory and Respiratory Systems
6. Regeneration and Growth: The Endocrine and Reproductive Systems 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. and the lymphatic system
To keep cells alive, the body needs a constant supply of oxygen and nutrients. it identifies and neutralizes foreign invaders
Powered by the heart—a muscle that pumps about 2,000 gallons of blood daily—this system uses a 60,000-mile network of vessels to transport life-sustaining fluid.