Since whales are mammals, they must breathe out of the water, like humans. Their respiratory system therefore functions similarly to that of land mammals, but has adaptations specific to their underwater environment.

When the animal inhales, air passes through the blowhole, nasal duct, larynx, trachea, and lastly the lungs. Same thing when it exhales, only in reverse! In large rorquals, the inhale-exhale cycle takes just a second or two. Additionally, whales have the ability to renew 90% of the air in their lungs with each breath. By comparison, in humans this figure is only 10 to 15%.

Blowhole

The blowhole or blowholes of whales are their equivalent of nostrils. Baleen whales have two blowholes, whereas toothed whales have just one. In toothed whales, the second nasal duct has changed function over the course of evolution: it is now used for echolocation.

During evolution, blowholes migrated to the top of the head, which facilitates breathing at the water surface. Whales cannot breathe through their mouth because, unlike terrestrial mammals, their digestive system and respiratory system are not connected. The blowhole leads to the nasopharynx, or nasal duct.

When the muscles are relaxed, the blowhole is closed by fibrous plugs that prevent water from entering the respiratory system. The whale must actively open its blowhole by contracting the muscles around it. Unlike land mammals, breathing in whales is therefore conscious.

Laryngeal sac

Only present in baleen whales, the laryngeal sac is an expandable structure that can hold air. It is associated with the larynx, between the blowhole and the trachea, and is surrounded by muscles. Its volume can vary based on the contraction or relaxation of these muscles. The function of the laryngeal sac is still a subject of debate amongst scientists.

In baleen whales, the laryngeal sac may help produce and amplify sounds. Changes in the sac’s volume are likely used to modify the intensity and frequency of sound waves. This hypothesis is supported by a similar structure found in frogs that allows them to produce their characteristic songs. Monkeys are also thought to use their laryngeal sac to howl without hyperventilating.

Baleen whales might also use their laryngeal sac to control their buoyancy when they dive. To do so, the whale can close off the passage between the laryngeal sac and the lungs, trapping a certain amount of air in the laryngeal sac. The animal can then reduce the volume of the laryngeal sac, which compresses the air and increases the pressure. The front part of the whale’s body becomes “denser” than the rear, allowing it to dive. To resurface, the animal could do the opposite by increasing the volume of the sac. This physiological adaptation is similar to the swim bladder in fish, a diverticulum associated with the esophagus that allows them to adjust their buoyancy.

Lungs

Air passes from the larynx to the trachea, a tube surrounded by cartilage and muscles. The trachea then divides into two bronchi that enter the lungs. The bronchi branch out into bronchioles that lead to alveoli, small sacs where gas exchange takes place: oxygen diffuses from the lungs into the blood and carbon dioxide moves in the opposite direction.

Whales’ lungs are proportionally less voluminous than those of land mammals, which may seem counterintuitive considering their impressive diving skills. But small lungs can minimize the tension associated with increased pressure at greater water depths.

The higher pressure experienced during a dive compresses the alveoli. Air is then pushed toward the bronchioles and bronchi, which do not collapse under pressure due to their cartilaginous wall. Gas exchanges are therefore greatly reduced during dives, which is believed to reduce the risk of decompression sickness.

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