The human circulatory system is a vital system that transports oxygen, nutrients, and hormones to the body's cells while removing waste products such as carbon dioxide. 
The heart acts as a double-stage pump, with a right side for pulmonary circulation and a left side for systemic circulation. Blood vessels include arteries (transporting oxygenated blood under high pressure), veins (returning deoxygenated blood) and capillaries (where exchanges take place).