Question

Why do veins have thin walls as compared to arteries?
A. Veins collect the blood from different organs and bring it back to the heart.
B. The blood in the vein is in lower pressure than artery.
C. The blood in the vein is in higher pressure than artery.
D. Both A and B.

Answer 1

The walls of arteries and veins consist of three layers or tunics.

Tunica Externa: The outermost layer and composed of connective tissues.
Tunica media: The middle layer and composed of smooth muscles.
Tunica interna: The inner layer and composed of elastic membrane and endothelium.
The middle layer i.e. Tunica media is thin in veins and thick in arteries.

Complete answer:
Blood vessels are the components of the circulatory system and form a tubular network which allows blood to transport throughout the body.These vessels transport blood,nutrients and oxygen to the tissues of the body.
There are 3 types of blood vessels:

Arteries: These blood vessels distribute blood from heart to all parts of the body (tissues, lungs, Brain etc.). All Arteries carry oxygenated blood. Arteriole is a small-diameter blood vessel that extends from an artery and leads to capillaries. Tunica media is thick and muscular because arteries function in a contractile manner and are subject to the high systolic pressure. So the pressure in arteries is under great pressure and it is highest when the heart contracts and lowest when the heart relaxes.
Veins: These blood vessels carry blood towards the heart from different parts of the body.All veins carry deoxygenated blood.Venule is a small-diameter blood vessel that extends from a vein and leads to capillaries. Tunica media is thin and has fewer muscles because veins do not function in a contractile manner and do not experience high systolic pressure. So the blood in veins is under low pressure.
Capillaries: These are the smallest blood vessels through which the exchange of gases and nutrients between the blood and tissue fluid occurs. The walls of capillaries are composed of simple squamous epithelium or endothelium.

So the correct answer is B.

Note: All arteries carry oxygenated blood and veins carry deoxygenated blood but there is an exception, the pulmonary artery carries deoxygenated blood to the organs and the pulmonary vein carries oxygenated blood to the heart.