Biology · Body Fluids and Circulation · NEET
Both arteries and veins have the same three coats. The innermost is the tunica intima, a lining of squamous endothelium. The middle is the tunica media, made of smooth muscle and elastic fibres. The outermost is the tunica externa, made of fibrous connective tissue with collagen fibres. NCERT states this word-for-word, so learn these three names in order.
The blood pumped by the ventricles enters arteries at high pressure. To take this pressure and to push blood forward by recoiling, arteries have a thick tunica media rich in smooth muscle and elastic fibres. NCERT says the tunica media is comparatively thin in the veins, because vein blood is at low pressure. So the layer that differs is the middle one, the tunica media.
No. This is the most common mistake. An artery is defined as a vessel that carries blood AWAY from the heart, not by the oxygen it carries. The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. Likewise, veins carry blood TO the heart, and the pulmonary veins carry oxygenated blood to the left atrium. Direction defines the vessel, not the oxygen.
Veins have valves. Because vein blood is at low pressure and often flows against gravity (for example, from the legs back to the heart), veins have valves that stop the blood from flowing backward. Arteries do not need valves inside them because the high arterial pressure keeps blood moving forward.
After large arteries, blood passes into smaller arterioles, and then into capillaries. Capillaries are the thinnest vessels: their wall is made of only the tunica intima, that is a single layer of endothelium. This thin wall is what allows exchange of oxygen, nutrients and carbon dioxide between blood and tissues. Blood is then collected by venules, then veins.
Blood pressure in the pulmonary artery is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. In both, the tunica intima is a single inner lining of squamous endothelium. The difference between arteries and veins is mainly in the thickness of the middle layer, the tunica media, which is thick in arteries and thin in veins.
A capillary wall is just one layer, the endothelium (tunica intima). It has no tunica media or externa. This single-cell-thick wall lets oxygen, nutrients and carbon dioxide diffuse between blood and tissue cells.
The elastic fibres in the tunica media let large arteries like the aorta stretch when the ventricle pumps and recoil between beats. This recoil keeps blood moving smoothly and maintains pressure, which is why arterial walls are both muscular and elastic.
The tunica media. It is thick and muscular in arteries to withstand high pressure, and comparatively thin in veins. This single fact is the most tested comparison for NEET.
