Penguins live in some of the coldest environments in the world. Temperatures can get as low as -60 degrees Celsius in Antarctica, which is enough to put off pretty much every animal, except the penguins. Their bodies are well protected with thick blubber and specialised feathers, which help to keep them warm. But penguins feet cannot be covered in feather or blubber (otherwise they wouldn’t be able to walk) and are in constant contact with the frozen surface. Furthermore, penguins feet are similar to other water loving birds like ducks, and have a large surface area. This helps them to swim, but is very bad for conserving heat, and typically would lose lots of heat. Yet the penguins feet do not freeze, and this is because of 3 key adaptations penguins have.
This is an adaptation most animals (including humans) have. In cold temperatures blood vessels constrict which reduces blood flow to the extremities of the body, which is where heat is easily lost.
This is because when warm blood from inside the body reaches the extremities the large surface area causes lots of heat to be lost. It then goes back into the core of the body(heart etc) where it needs to be warmed. heat is transferred from the core of the body to the blood, which cools the core, and makes you feel very cold. Blood then goes back out to the extremities, and loses the heat all over again. This can obviously lead to large amounts of heat being lost. In cold conditions, you want to minimise the amount of warmth being lost in the extremities, and a very effective way of doing this is reducing the blood flow to these parts. Enough blood will travel to the extremities to keep them alive, but that’s about it. This is why your hands will look white in cold weather – less blood is being sent to them
This adaptation is not as common as the previous, but many birds do share this. At the top of penguins legs are a complex of arteries and veins. The arteries are carrying warm blood to the feet, and the veins are carrying very cold blood away. As already mentioned, you do not want cold blood in the body, or warm blood in the feet because this causes lots of precious heat to be lost. This complex of veins and arteries at the top of the leg transfers all the heat from the outgoing arteries to the incoming blood in the veins, and takes in all the cold of the incoming veins to the outgoing arteries (as shown in the image on the right from Biology Pages).
This minimises heat loss through the extremities because it keeps the heat exchange inside the body, rather than outside.
This final adaptation is very impressive, and something that very very few animals have. When oxygen binds to hemoglobin it gives out heat (exothermic reaction), and when is unbinds, it requires heat (endothermic reaction). If the conditions of the unbinding are different to the binding (pH etc) it can result in a net loss or even gain of energy (or heat) in parts of the body. The difference in energy between binding and unbinding is called ΔH, and compared to humans, penguins have a very modest ΔH, which means loss of energy is minimal. Furthermore, low temperatures prevent unbinding (requiring heat) of oxygen, so in parts of the body which are cold this reaction (heat taking) wouldn’t occur. This prevents heat loss from the feet, where it is the most important.
Some animals have taken this mechanism even further. Tuna have the right conditions in their body to raise their body temperature 17 degrees celsius about their surroundings!
All these adaptations carefully keep the penguins feet just above freezing (1-2 degrees celsius), which prevents their feet freezing, and minimises energy/ heat loss.
Despite terribly cold conditions, penguins have 3 very important adaptations which prevent their feet freezing. The first is the ability to limit the amount of blood that goes to the feet – providing just enough to keep the feet alive and unfrozen. The second is due to a countercurrent heat exchange at the top of the penguins legs, which ensures cold blood going into the body from the feet is warmed, and blood going to the feet is cooled. The third is a cleaver the ability to regulate the exothermic and endothermic reactions of oxygen binding to heamoglobin, which minimises heat being taken from extremities like the feet.
Image courtesy of StormPetrel1
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Penguins can control the amount of blood that goes into their feet, and how much it gets heated. But most interestingly, penguins can conserve heat in their feet by controlling the amount of exotherminc reactions (giving out heat) and endothermic reactions (requiring heat) that take place.