Whales are mammoth creatures and are mammals; both factors that may make the assumption that they have enormous lungs seem to be quite reasonable. However, this is not actually the case. In fact, the lungs of the whales are quite small in proportion to their bodies. Due to the depths to which whales dive and the accumulation of potentially harmful gases, it would actually be dangerous for whales to have large lungs.
As a whale breathes air in through the blowhole at the top of its head, the air enters the lungs, oxygenates the blood and travels through the body to feed all of the tissues. The gases in the air dissolve in the fluids of the body. These gases include nitrogen. As the whale descends deeper and deeper into the ocean, the air has to become more and more compressed. This will force more of the gases to be dissolved into the tissues. If the lungs were really large, more nitrogen (for example) would be able to be contained and then absorbed, which would create toxicity in the body. If the whale ascended too quickly with all that gas absorbed in the tissues and not enough in the lungs, it would lead to the Bends (or decompression sickness).
Therefore, the lungs are fairly small and the animal has adapted so that it can retain as much oxygen as possible while diving down to impressive depths.
The very flexible ribcage can expand and, more importantly, cave in with pressure, which prevents the collapse of the lungs. Air leaves the lungs as they experience increased pressure, being pushed into air passages, eventually ending up in the bronchioles so that even the alveolar sacs may collapse. In the bronchioles, no gas exchange takes place, protecting the tissues from being subjected to concentrated amounts of nitrogen.
Whales do not need to store oxygen in their lungs to survive. They can actually store large percentages of their oxygen in circulation around their body. Human beings have to store about 36% of the oxygen that they inhale in the lungs. Whales, though, can store about 75% of their oxygen in their circulatory system.
On average, a whale can hold its breath for between 10 and 60 minutes, depending on the species. The enormous Blue Whale has a lung capacity of approximately 5 000 litres.
Understanding the role of the lungs in whales reveals a little more about their incredible adaptation and the mechanisms that they use to adjust to their marine environment; making these animals just a little less mysterious to human beings.
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