The Amazing Bodies Of Dolphins
Dolphins have a number of extraordinary features so that they can thrive in their watery world.
The most obvious thing that dolphins need is air. They glide through the water so effortlessly, surfacing every few minutes to take a breath. Dolphins can dive to 200 m (600 ft).
Marine mammals take more air with each breath than other mammals, and they exchange more of the air in their lungs with each breath.
Their red blood cells can hold more oxygen and they have a much higher tolerance for carbon dioxide than we do. During each breath they exchange 80% of the air in their lungs, while humans only exchange 17%.
Even so, given the size of their lungs, they should run out of oxygen and drown before they can get that deep! How do they do it?
When diving, they cut off blood circulation to their skin digestive system and extremities, leaving only the heart, brain and tail muscles working. However, even these measures give insufficient time to plummet to those depths.
Dolphins and other marine mammals don’t get the bends (nitrogen narcosis) when they plummet to the depths of the ocean.
In human lungs, air remains all throughout the lungs and gas exchange continues in the alvoli, allowing nitrogen to be forced into the blood.
The alvoli of doplhins collapse at 3 atm of pressure, forcing the air back into the bronchioles where gas exchange does not take place.
How do dolphins (and whales) sleep without drowning?
Marine mammals have two basic methods of sleeping: they either rest quietly in the water, or sleep while swimming slowly next to another animal.
Dolphins also enter a deeper form of sleep at night where they become like a log floating on the water. When a baby dolphin is born it does not have enough body fat to float easily.
The baby stays afloat by being towed in its mother’s slipstream or wake even when it is sleeping. This means that the mother cannot stop swimming for the first several weeks of her baby’s life!
To avoid drowning, it is crucial that cetaceans retain control of their blowhole and recognize when it is at the surface. When sleeping, dolphins shut down half of their brain and one eye.
The other half stays awake at a lower level of alertness. The semi-conscious side watches for predators, obstacles, and signals when to rise to the surface for a breath of air.
After 2 hours, things are reversed, the active side goes to sleep and the rested side looks after vital functions. Amazing!
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Pass it on: Popular Science