ナショナルジオグラフィックさんのインスタグラム写真 - (ナショナルジオグラフィックInstagram)「Photo by @jasperdoest | Penguins, like other birds in cold climates, have adaptations to avoid losing too much heat and to preserve a central body temperature of about 40°C. The feet pose particular problems since they cannot be covered with insulation in the form of feathers or blubber yet have a wide surface area. Two mechanisms are at work. First, the penguin can control the rate of blood flow to the feet by varying the diameter of arterial vessels supplying the blood. In cold conditions the flow is reduced; when it is warm the flow increases. However, penguins also have countercurrent heat exchangers at the top of the legs. Arteries supplying warm blood to the feet break up into many small vessels that are closely allied to similar numbers of venous vessels bringing cold blood back from the feet. Heat flows from the warm blood to the cold blood. This way penguin feet are held a degree or two above freezing—to minimise heat loss while avoiding frostbite. Follow @jasperdoest for more images of the wonders of nature and the human-wildlife relationship. #onassignment @natgeoexpeditions #penguin #feet #bird #winter」11月26日 5時29分