Body’s Circulatory System
Arteries and veins are essential components of the circulatory system in vertebrates. Working in tandem, they ensure blood circulates throughout the body, delivering oxygen and nutrients while carrying away waste products with every heartbeat. Generally, arteries transport oxygen-rich blood away from the heart, whereas veins return oxygen-poor blood back to it. A simple way to remember this is “A for artery and away from the heart.”
The main exceptions are the pulmonary vessels: pulmonary arteries carry deoxygenated blood from the heart to the lungs, while pulmonary veins bring oxygenated blood back to the heart.
Because arteries are located closest to the heart, they endure high pressure from the forceful flow of blood. Their thicker walls allow them to withstand this pressure, and they expand and contract with each heartbeat—hence why the pulse is measured from an artery. Veins, on the other hand, function under much lower pressure but face the challenge of gravity when moving blood from the limbs back to the heart. To aid this process, many veins—particularly those in the legs—are equipped with valves that stop blood from flowing backward or pooling.
Although veins are frequently shown as blue in medical illustrations and can look bluish beneath lighter skin, they are not actually blue. The color results from the way light interacts with skin ad with deoxygenated blood, which is a darker red. In reality, veins observed during surgery or in preserved bodies appear very similar in color to arteries.