how does countercurrent flow conserve body heat for animals

how does countercurrent flow conserve body heat for animals who live in cold water?

Solution

Countercurrent heat exchange is used in animals living in extreme conditions of cold weather as a mechanism for retaining the heat . Countercurrent heat exchange systems are made up of a complex network of peri-arterial venous plexuses. Each plexus consists of an artery containing warm blood coming from the heart surrounded by a bundle of veins containing cool blood from the body surface. As these fluids flow past each other, they create a heat gradient in which heat is transferred and retained inside the body. The warm arterial blood transfers most of its heat to the cool venous blood now coming in from the outside. This conserves heat by recirculating it back to the body core.