To permit material exchange between blood and tissues.
Actually, it is the opposite. Tunica media is thicker in arteries not in veins.While, the tunica adventitia is thicher in veins.
Because capillaries are very thin. many times as few as one red blood cell wide, and only have enough room for a layer of endothelial tissue, in the form of the Tunica Intima.
1 reabsorption of useful substance like glucose2 filteration and removal of waste materials like urea3 secrtion of certain substance like h+
The 3 main functions are: Produces motion, provides stabilization, and generates heat.