What is the role of the circulatory system?

• A. It carries air to the lungs
• B. It stores nutrients only
• C. It controls hormonal secretions
• D. It pumps blood to the lungs and digestive system to pick up oxygen and nutrients, then delivers these to body cells and removes wastes

Answer: (D)

The circulatory system acts as the body's transport network, moving blood through the heart, a vast network of vessels, and the blood itself to serve every cell. It pumps blood to the lungs so red blood cells can pick up oxygen and release carbon dioxide, and it sends blood to the digestive system to pick up nutrients from digested food. From there, blood carries these oxygen and nutrient supplies to all body cells, where they power cellular processes. At the same time, waste products produced by metabolism—like carbon dioxide and other metabolites—are picked up by the blood and carried away to be eliminated by the lungs, kidneys, and other organs. While the circulatory system interacts with respiration and digestion, its main role is transporting oxygen, nutrients, and wastes throughout the body, not carrying air to the lungs, storing nutrients, or directly controlling hormonal secretions.