Veins - GCSE Biology Definition

Veins are blood vessels that carry blood towards the heart. In the human body, they have thin walls and often contain valves to prevent the blood from flowing backwards. Unlike arteries, which carry oxygen-rich blood away from the heart, most veins carry blood that is low in oxygen back to the heart to be re-oxygenated in the lungs. An important exception is the pulmonary vein, which carries oxygenated blood from the lungs to the heart. Veins play a crucial role in the circulatory system by ensuring blood flows smoothly and continuously throughout the body.