👉 Veins are blood vessels that carry deoxygenated blood from the body's tissues back to the heart. They have thinner walls and larger lumens compared to arteries, which allows them to accommodate blood with lower pressure. Veins contain one-way valves that prevent blood from flowing backward and ensure it moves toward the heart. When standing or exercising, muscles contract to help push blood back up through the veins, overcoming gravity's pull.
