Capillaries

• tiny vessels made of a single layer of endothelial cells - short diffusion path
• velocity of blood slowest through carpillaries due to large sectional cross area - increased exchange if blood flow slow
• Small size increases surface area to volume ratio - this along with slow flow and thin walls allow efficient exchange between the blood and the tissue
• some carpillaries have gaps between adjacent endothelial cells called fenestrations - faster diffusion rates between carpillaries and tissues - found where high exchange rates needed
• Network of carpillaries in tissues are called capillary beds