Describe the structure and function of arteries, veins, and capillaries in the circulatory system.

Arteries are blood vessels that carry blood away from the heart. They have thick, muscular, and elastic walls to withstand the high pressure of blood pumped from the heart. This elasticity allows them to expand and recoil, helping to propel blood.

Veins are blood vessels that carry blood towards the heart. They have thinner and less muscular walls compared to arteries, as the blood pressure within them is much lower. Many veins, especially in the limbs, contain valves to prevent the backflow of blood, ensuring it flows in one direction towards the heart.

Capillaries are the smallest blood vessels, forming a network between arterioles (small arteries) and venules (small veins). Their walls are extremely thin, typically only one cell thick, which facilitates the efficient exchange of oxygen, nutrients, and waste products between the blood and the surrounding tissues.

$\boxed{\text{Arteries carry blood away from the heart, having thick, elastic walls. Veins carry blood towards the heart, with thinner walls and often containing valves to prevent backflow. Capillaries are tiny, thin-walled vessels where the exchange of substances between blood and tissues occurs.}}$