There are three main types of blood vessels: arteries, capillaries, and veins. Arteries carry oxygenated blood away from the heart and branch into smaller vessels before becoming capillaries. Capillaries allow for the exchange of nutrients, gases, and waste between blood and tissues. Veins carry deoxygenated blood back to the heart. Arteries have thick muscular walls to withstand high blood pressure from the heart, while veins have thinner walls and valves to prevent backflow of blood at low pressure.