Explore how capillary walls, branching, lumen size and fenestrations support rapid exchange between blood and surrounding tissues in IB Biology SL B3.2.1.
Explain how the structure of capillaries relates to their functions.
Capillary walls are thin or one cell thick for better diffusion. Capillaries have a small diameter or narrow lumen so they fit into small spaces between cells. Their small diameter gives a greater surface area for molecular exchange. Pores between cells in the walls allow plasma to leak out and allow phagocytes or immune components to enter tissues. Only one red blood cell passes at a time, allowing efficient oxygen uptake.