Countercurrent Exchange in Biological Systems
Countercurrent exchange in biological systems was discovered and studied following the discovery of Countercurrent multiplication systems by Werner Kuhn.
Countercurrent exchange is used extensively in biological systems for a wide variety of purposes. For example, fish use it in their gills to transfer oxygen from the surrounding water into their blood, and birds use a countercurrent heat exchanger between blood vessels in their legs to keep heat concentrated within their bodies. In vertebrates this type of organ is referred to as a Rete mirabile (originally the name of the organ in the fish gills). Mammalian kidneys use countercurrent exchange to remove water from urine so the body can retain water used to move the nitrogenous waste products (see Countercurrent multiplier).
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