Countercurrent Exchangers

Countercurrent exchangers are systems that involve the anti-parallel flow of two media that never mix. This allows specific substances that can pass the boundary between the two fluids (eg. gases or heat) to be exchanged without the media themselves mixing. Anti-parallel flow allows a higher concentration of the substance to be exchanged across the media, for example this is how any fish with gills, obtains enough oxygen to “breathe” underwater.

In the context of the body’s circulatory system in thermal homeostasis, this allows heat to be exchanged from warm effluent blood, originating from the heart, to cold influent arterial vessels flowing from the extremities. This limits the amount of body heat that reaches the extremities where it is likely to be released to the external environment through various heat exchange methods to the external environment.