PATHOLOGY

Detailed explanation-1: -The walls of capillaries are just one cell thick. Capillaries therefore allow molecules to diffuse across the capillary walls. This exchange of molecules is not possible across the walls of other types of blood vessel because the walls are too thick.

Detailed explanation-2: -Capillaries measure 5-10 m in diameter and are only one cell thick. Capillaries connect arterioles and venules and enable the exchange of water, oxygen, carbon dioxide, and many other nutrients and waste substances between blood and surrounding tissues.

Detailed explanation-3: -Explanation: Capillaries are one cell thick so that diffusion of gases and other substances like urea, nutrients, water, etc becomes easier.