Arteries have thick, muscular and elastic walls with relatively narrow lumens, whereas veins have thinner walls, wider lumens and often contain valves. These differences adapt arteries to high-pressure blood flow and veins to low-pressure blood return.
This content in B3.2 Transport is required at both SL and HL.
| Structural feature | Arteries | Veins |
|---|---|---|
| Wall thickness | Thick relative to the lumen | Thin relative to the lumen |
| Smooth muscle | Thick layer | Thinner layer |
| Elastic tissue | Abundant | Less abundant |
| Lumen | Relatively narrow | Relatively wide |
| Valves | Absent along the vessel | Present in many veins, especially in the limbs |
| Appearance in a transverse section | Usually round and maintains its shape | Often irregular or collapsed |
Arteries carry blood away from the heart under high pressure. Their thick layer of smooth muscle withstands this pressure and can alter vessel diameter. Elastic fibres allow the wall to stretch during ventricular contraction and recoil afterward, helping maintain pressure and continuous blood flow between heartbeats.
Veins return blood to the heart at much lower pressure. They therefore require less smooth muscle and elastic tissue. Their wide lumen reduces resistance to blood flow, while valves prevent backflow; contraction of nearby skeletal muscles compresses veins and helps move blood toward the heart.
A common misconception is that arteries always carry oxygenated blood and veins always carry deoxygenated blood. They are actually classified by the direction of blood flow: arteries carry blood away from the heart, while veins carry it toward the heart. The pulmonary artery and pulmonary vein are important exceptions to the oxygenation pattern.
Exam technique: When asked to distinguish arteries from veins in a micrograph, compare both vessels directly. Use wall thickness relative to lumen diameter and the presence of valves; do not rely on oxygen content or vessel size alone.
