NEET BIOLOGY

Detailed explanation-1: -A vein is a blood vessel that conducts blood toward the heart. Compared to arteries, veins are thin-walled vessels with large and irregular lumens (see Figure 6).

Detailed explanation-2: -Arteries have thick, muscular walls and relatively small lumens. They also possess a membrane of elastic fibers, that helps them to stretch and withstand the pressure of the constant pumping by the heart without being damaged. Unlike veins, arteries do not possess valves.

Detailed explanation-3: -Capillaries are thin-walled vessels composed of a single endothelial layer. Because of the thin walls of the capillary, the exchange of nutrients and metabolites occurs primarily via diffusion. The arteriolar lumen regulates the flow of blood through the capillaries.

Detailed explanation-4: -Veins carry unoxygenated blood towards the heart, away from tissues at low pressure so the lumen is large. Blood moves more slower and often against gravity so valves and a larger lumen ensure it is still transported efficiently.

Detailed explanation-5: -The ventricles of the heart have thicker muscular walls than the atria. This is because blood is pumped out of the heart at greater pressure from these chambers compared to the atria.