revision preference src: The short distance is important because the capillary diffusion rate decreases when the diffusion distance increases. Then, because of its large number (10-14 million capillaries), there is an incredible amount of surface area for exchange. <SEP> tgt: The short distance is important because the capillary diffusion rate decreases when the diffusion distance increases. Because of its large number (10-14 million capillaries), there is an incredible amount of surface area for exchange.