Nature Company Guides, Time Life Book Series. Weldon Owen Pty Ltd San Francisco. Respiration The shark extracts oxygen from the water to metabolize their food. The gills are found on five to seven vertical arches that form the walls of the external gill slits. In a seperate chamber beneath the gills, the heart pumps oxygen-depleted blood to capillary beds in the arches.
Water is pumped into the mouth and out across the gills counter to the direction of blood flow.
This exchange system greatly enhances the rate and efficiency of oxygen diffusion into the blood. Photo modified from Sharks and Rays . L Taylor. 1997. Nature Company Guides, Time Life Book Series. Weldon Owen Pty Ltd San Francisco.