Veins and arteries are the two main types of blood vessels that play essential roles in the circulatory system, each with distinct structures and functions to facilitate blood flow throughout the body.

Arteries: Arteries carry oxygen-rich blood from the heart to the body’s tissues. They have thick, elastic walls composed of three layers: the tunica intima (inner layer), tunica media (muscular layer), and tunica adventitia (outer layer). The elasticity of arteries allows them to expand and contract as blood is pumped by the heart, helping maintain blood pressure and efficient circulation. Large arteries like the aorta distribute blood to smaller arteries, which eventually branch into arterioles and capillaries, where gas and nutrient exchange occurs.

Veins: Veins carry blood back to the heart, usually transporting carbon dioxide and metabolic waste from the tissues. Veins have thinner and less elastic walls than arteries, consisting of the same three layers but with less smooth muscle and elastic tissue. Many veins, especially in the lower extremities, contain one-way valves that prevent blood from flowing backward, ensuring it moves in the correct direction toward the heart. Smaller veins, called venules, merge to form larger veins, which eventually converge into major veins like the superior and inferior vena cava, returning blood to the heart for reoxygenation.