Jan 22, 2022 12:00:00

Why can sea otters keep their body temperature even in the cold sea?

Mammals, which are homeothermic animals , can maintain a constant body temperature even when the outside temperature changes, but it is difficult for mammals living in water, where the body temperature is more easily deprived than in the air, to maintain a constant body temperature. Sea otters, among other aquatic mammals, live in cold waters such as the Sea of Okhotsk and the coast of North America, despite their small size and easy heat escape. Researchers at Texas A & M University explain the question, 'How does a sea otter keep its body temperature in the cold sea?'

Sea otters demonstrate that there is more to muscle than just movement – it can also bring the heat
https://theconversation.com/sea-otters-demonstrate-that-there-is-more-to-muscle-than-just-movement-it-can-also-bring-the-heat-165804

Many aquatic mammals have a thick layer of fat for insulation because water deprives them of body temperature faster than air, but smaller sea otters do not have thick fat. Instead, sea otters have a fur with an astonishing density of 1 million hairs per square inch (about 6.45 square centimeters), and the layer of air taken into this fur acts as a thermal insulator. That thing.

Maintaining this fur is quite difficult, and 10% of the sea otter's daily activities are used to maintain the air in the fur. You can see how the sea otter grooms her hair carefully in the following movie.

Grooming Otter-YouTube


However, no matter how dense the fur prevents the release of heat, that alone does not mean that sea otters can survive in the cold waters. Sea otters use the body's metabolic function to maintain body temperature, and their metabolic rate is about three times higher than that of terrestrial mammals of similar size. Good metabolism means inefficient energy, and while humans need about 2% of their body weight per day, sea otters must eat more than 20% of their body weight per day. It will not be. Applying the food intake of sea otters to a person weighing 70 kg, it is calculated that 14 kg or more of food is required per day.

Food ingested by animals cannot be used as is, it is first broken down by the digestive system into nutrients such as fat and sugar, then carried by the blood and absorbed by cells of various tissues of the body. Then, a small organ called mitochondria inside the cell converts the nutrients taken in into adenosine triphosphate (ATP), which is also called the 'energy currency of the living body', and the cell works using this ATP as energy.

In the process of converting nutrients to ATP in mitochondria, some nutrients are not converted to ATP and are released as heat energy, and many vertebrates intentionally lower the ATP conversion efficiency to generate heat. .. All tissues in the body produce heat along with metabolism, but muscles, which make up about 30% of the body weight of mammals, consume a particularly large amount of energy to produce heat. Exercise heats your body because your muscles metabolize nutrients into heat.

A study of sea otter metabolic function by teams such as Texas A & M University, Alaska Southeast University, and Monterey Bay Aquarium found muscle samples from sea otters of all ages and sizes, from babies to adults, with oxygen consumption. It was placed in a small, measurable room to monitor how much energy the muscle tissue used.

Using a variety of methods to stimulate metabolic processes, we measured the amount of energy mitochondria used to produce ATP and the amount of energy converted to heat, and found that sea otter muscles were 'very inefficient.' In other words, a lot of energy is emitted as heat without being converted to ATP, which played an important role for sea otters to maintain their body temperature in the cold sea. Surprisingly, we also found that baby muscles that cannot swim on their own have the same metabolic capacity as adults.

'Our research shows that muscles clearly have a more important role than just movement. Muscles make up the majority of body weight, so a slight increase in muscle metabolism. Even can dramatically increase the amount of energy used. '

If future research develops a 'safe and reversible way to increase resting skeletal muscle metabolism,' doctors can also increase the amount of calories burned by patients to control obesity. On the contrary, the research team argued that if 'a method to reduce skeletal muscle metabolism' is developed, it will be possible to reduce the amount of food and resources required for long space trips.