An artery is a blood vessel that carries blood away from the heart.
Arteries receive blood under relatively high pressure as the heart contracts, so their walls are generally thicker and more elastic than those of veins. The largest artery is the aorta, which leaves the left ventricle and branches into systemic arteries supplying the body. Smaller branches are called arterioles, which help regulate blood flow and blood pressure.
A common mix-up is that arteries always carry oxygen-rich blood. In fact, the pulmonary arteries carry oxygen-poor blood from the right side of the heart to the lungs, where it gains oxygen. In fetal circulation, the umbilical arteries also carry deoxygenated blood. The definition is based on direction—away from the heart—not oxygen content.
Veins carry blood toward the heart, while capillaries form microscopic networks between arterioles and venules. Capillaries are where oxygen, nutrients, carbon dioxide and wastes move between blood and tissues. The pulse felt at the wrist or neck reflects pressure waves traveling through arteries after each heartbeat.