The human heart pumps blood through three main types of blood vessels - arteries, veins, and capillaries. Arteries carry oxygenated blood away from the heart to tissues, while veins carry deoxygenated blood back to the heart. Capillaries allow for the exchange of oxygen, carbon dioxide, and other substances between blood and tissues. The circulatory system transports blood from the heart to the lungs and throughout the body, providing oxygen and nutrients and removing waste. Human blood contains plasma, red blood cells, white blood cells, and platelets, each with different functions in transportation and defense.