NREMT Paramedic

Answer: C - Capillaries are the only blood vessels with thin enough walls to allow the exchange of oxygen and carbon dioxide between blood and the cells. As blood flows to each part of the body, it delivers fresh oxygen that diffuses through the capillary walls and into the membranes of the cells. It simultaneously absorbs carbon dioxide which has been produced by the cells and delivers the carbon dioxide to the lungs for elimination from the body. Arteries, arterioles, veins, and venules are larger blood vessels, with walls that are too thick to allow sufficient diffusion of gases between blood and cells.