In cetology, a blowhole is the hole at the top of a Cetacean's head through which the animal breathes air. It is homologous with the nostril of other mammals. As whales reach the water surface to breathe, they will forcefully expel air through the blowhole. Not only is air expelled, but so are mucus and carbon dioxide from the animal's metabolism, which have been stored in the whale while diving. The exhalation is released into the comparably lower-pressure, colder atmosphere, and any water vapor condenses. This spray, known as the blow, is often visible from far away as a white splash, which can also be caused by water resting on top of the blowhole.
Air sacs just below the blowhole allow whales to produce sounds for communication and (for those species capable of it) echolocation. These air sacs are filled with air, which is then released again to produce sound in a similar fashion to releasing air from a balloon.
Baleen whales have two blowholes positioned in a V-shape while toothed whales have only one blowhole. The blowhole of a sperm whale, a toothed whale, is located left of centre in the frontal area of the snout, and is actually its left nostril, while the right nostril lacks an opening to the surface despite the fact that its nasal passage is otherwise well developed.
The trachea only connects to the blowhole and there is no connection to the esophagus as with humans and most other mammals. Because of this, there is no risk of food accidentally ending up in the animal's lungs, and likewise the animal cannot breathe through its mouth. As a consequence, whales have no pharyngeal reflex.
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