Innovation and Speciation: aquatic mammals avoid bends (Evolution)

by David Turell , Wednesday, April 25, 2018, 23:41 (2402 days ago) @ David Turell

The 'bends' is a diving problem for any diving animal; it is a trapping of nitrogen bubbles in tissue. The aquatic mammals have a solution:

https://www.sciencedaily.com/releases/2018/04/180425093810.htm

"Deep-diving whales and other marine mammals can get the bends -- the same painful and potentially life-threatening decompression sickness that strikes scuba divers who surface too quickly. A new study offers a hypothesis of how marine mammals generally avoid getting the bends and how they can succumb under stressful conditions.

"The key is the unusual lung architecture of whales, dolphins and porpoises (and possibly other breath-holding diving vertebrates), which creates two different pulmonary regions under deep-sea pressure, say researchers at the Woods Hole Oceanographic Institution (WHOI) and the Fundacion Oceanografic in Spain.

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"When air-breathing mammals dive to high-pressure depths, their lungs compress. That collapses their alveoli -- the tiny sacs at the end of the airways where gas exchange occurs. Nitrogen bubbles build up in the animals' bloodstream and tissue. If they ascend slowly, the nitrogen can return to the lungs and be exhaled. But if they ascend too fast, the nitrogen bubbles don't have time to diffuse back into the lungs. Under less pressure at shallower depths, the nitrogen bubbles expand in the bloodstream and tissue, causing pain and damage.

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"In their study, the researchers took CT images of a deceased dolphin, seal, and a domestic pig pressurized in a hyperbaric chamber. The team was able to see how the marine mammals' lung architecture creates two pulmonary regions: one air-filled and the other collapsed. The researchers believe that blood flows mainly through the collapsed region of the lungs. That causes what is called a ventilation-perfusion mismatch, which allows some oxygen and carbon dioxide to be absorbed by the animal's bloodstream, while minimizing or preventing the exchange of nitrogen. This is possible because each gas has a different solubility in the blood. The terrestrial pig did not show that structural adaptation.

"This mechanism would protect cetaceans from taking up excessive amounts of nitrogen and thus minimize risk of the bends, says lead author Daniel García-Parraga of the Fundacion Oceanografic."

Comment: This is another example of the physiological stresses that had to be overcome to arrange for the evolution of aquatic mammals. It doesn't make sense that evolution would not have taken the easiest course, but it didn't. Chance evolution would have made easy changes. This makes the case for God intervening for whatever reason He had.