do capillaries allow diffusion
Capillary to Tissue Fluid Exchange. Capillaries are where fluids, gasses, nutrients, and wastes are exchanged between the blood and body tissues by diffusion. Capillary walls contain small pores that allow certain substances to pass into and out of the blood vessel.
Veins are blood vessels that bring blood back to the heart and drain blood from organs and limbs. Capillaries have one layer of cells (the endothelial tunic or tunica intima) where diffusion and exchange of materials takes place.