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Whales are one of the aquatic mammal species. Marine mammals have a significant difference from the mammal species living on land. They can hold their breath for a very long time under the water. For example, while people can hold their breath for a few minutes at most, some whale species can stay under water without breathing for two hours.
This feature of whales can be thought to be related to the size of their lungs. In fact, compared to their body size, the lungs of marine mammals are smaller than that of mammals living on land. Because the whales' lungs do not function as an oxygen tank under water. The main reason why marine mammals can hold their breath under water for a long time is that they can use the oxygen they take efficiently for a long time.
Respiratory and cardiovascular systems of marine mammals have different features than other mammal species living on land. For example, the ratio of blood volume to body volume in marine mammals is about 3-4 times higher than in human. The rate of hemoglobin (the oxygen-carrying protein in the blood) in their blood is about twice that in humans. The rate of myoglobin, which is the protein that stores oxygen in muscle tissues in marine mammals, is 10-20 times higher than in humans. Also, in order to reduce oxygen consumption under water as much as possible, the whales' heart rate decreases and the blood is pumped only to the necessary organs such as the heart, brain and muscles.