Pump It Up: The Heart and Blood

The average human adult has about a gallon (4 liters) of blood circulating through a network of blood vessels 62,137 miles (100,000 kilometers) long. Learn about the heart, arteries, veins, and the different components that make up blood, from the red blood cells down to the hemoglobin molecules, and the functions they perform. Also discover where blood forms and what scientific advancements there have been in trying to create a blood substitute.