The blood vessels in the human body form a complex network that transports blood, oxygen and nutrients to all tissues. They are divided into five main types: arteries, arterioles, capillaries, venules and veins, each adapted to a specific function in the bloodstream.
Arteries, such as the aorta, transport oxygenated blood from the heart to the organs under high pressure, thanks to their thick, elastic walls. 
Veins return deoxygenated blood to the heart at low pressure, while capillaries ensure gas and nutrient exchange with tissues via their thin walls.