What does the heart circulate throughout the body?

The heart circulates blood throughout the body. Blood serves as a vital transportation system that carries not only oxygen and nutrients but also hormones, waste products, and immune cells. The heart's pumping action moves oxygenated blood from the lungs to the tissues and organs, and then returns deoxygenated blood back to the lungs to be re-oxygenated. This continuous cycle is crucial for maintaining homeostasis and ensuring that every cell in the body receives the necessary substances for proper function. In this context, while oxygen, nutrients, and hormones are significant components transported by the blood, they are not what is actively circulated; rather, it is the blood itself that is being pumped and moved throughout the body.