AP BIOLOGY

Detailed explanation-1: -Blood flow through vein does not exert pressure on the walls of veins. Due to this, they do not need thick walls. Hence, veins have thin walls as compared to arteries.

Detailed explanation-2: -Since the blood pumped from the heart into the arteries flows at higher pressure than the blood in veins, hence arteries need to have thicker walls or else the high blood pressure might cause them to burst.

Detailed explanation-3: -Blood flows from venules into larger veins. Just like the arterial system, three layers make up the vein walls. But unlike the arteries, the venous pressure is low. Veins are thin-walled and are less elastic.

Detailed explanation-4: -It is because arteries carry blood from the heart. They can withstand pressure because of their thick walls. Veins have thin walls due to the low pressure.