Whales do not breathe through their mouths, but rather through a nostril, or blowhole, located on the top of the head. Toothed whales have only a single blowhole; baleen whales have two blowholes. The blowhole opens by a slight muscular contraction and closes automatically when the muscle relaxes. As a whale surfaces it exhales through the blowhole, creating a loud sound and characteristic cloud of mist known as the spout. The spout is caused by condensation from the exhaled warm, moist air, not from seawater trapped in the blowhole, as was once believed.
Air taken in through the blowhole travels through the trachea (windpipe) to the lungs. Unlike for most land animals, the trachea does not connect to the throat. So when the whale opens its mouth underwater to feed, water does not rush into the lungs as it would in land animals. This structural arrangement enables the whale to breathe air and swallow food at the same time.
The lungs transfer oxygen to the blood while removing the blood’s carbon dioxide. Relative to body size, whale lungs are proportionally somewhat smaller than human lungs. But whale lungs are far more efficient: While human lungs exchange about 15 to 20 percent of their contents with each breath, whale lungs exchange about 90 percent with each breath. This means that whales can take up oxygen and dispose of carbon dioxide much faster than humans, enabling them to hold their breath underwater for long periods.
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