The whale lung is a biological structure perfectly adapted to the extreme environment of the deep ocean. As air-breathing mammals, whales must periodically return to the surface, yet they remain submerged for extended periods and dive to crushing depths. Their respiratory system is fundamentally different from that of terrestrial mammals, functioning less like a continuous oxygen supply and more like a highly efficient, single-use air reservoir. This organ must manage the paradox of rapid air exchange at the surface while withstanding immense hydrostatic pressure deep below the waves.
Unique Anatomy and Scale
The blue whale possesses the largest lungs on the planet, with a combined capacity of approximately 5,000 liters of air—roughly 1,000 times that of an average human lung. Despite this size, a whale’s lungs are proportionally smaller than a human’s, occupying only about 3% of its internal body cavity, compared to 7% in people. This decrease in size is a powerful adaptation, limiting the total volume of air and, critically, the nitrogen gas, taken on a dive.
The respiratory tract begins with the blowhole, positioned on top of the head to facilitate quick breathing while minimizing the body exposed above water. Baleen whales, such as the blue whale, have two blowholes, while toothed whales possess only one. Unlike terrestrial mammals, the whale’s respiratory system is entirely separate from its digestive tract, preventing water from being inhaled during feeding or breaching.
Powerful sphincter muscles surrounding the blowhole keep it tightly sealed when the whale is submerged. The cetacean chest cavity also differs significantly from a human’s, exhibiting a relative lack of rigidity. This flexible thorax allows the chest wall to compress under external water pressure, preventing the negative internal pressures that cause lung trauma, a condition known as “lung squeeze,” in diving humans.
The Mechanics of Rapid Air Exchange
When a whale surfaces, its breathing is a deliberate, conscious act, unlike the involuntary breathing of humans. The process of ventilation, often called the “blow,” is characterized by extraordinary speed and efficiency. A large whale can replace its entire 5,000-liter lung volume in a remarkably short time, sometimes as quickly as two seconds.
This rapid air exchange is achieved through a near-complete ventilation of the lung volume. Whales can exchange between 80% and 90% of the air in their lungs with each breath, which is far more efficient than the 10% to 15% exchange rate typical of humans. The exhalation itself is a forceful event, with the air jetting out at speeds that can exceed 600 kilometers per hour, creating the visible spout.
The anatomical structures within the lung are specialized to handle this high volume and speed. The extensive surface area of the alveoli allows for extremely quick gas exchange, maximizing the oxygen absorbed during the brief time at the surface.
Pressure Management During Deep Dives
The most complex function of the whale lung is its response to the crushing hydrostatic pressure encountered during deep dives. As a whale descends, the water pressure increases dramatically, compressing the air inside the lungs. This compression is the basis for the whale’s strategy to avoid decompression sickness, often called “the bends.”
The core adaptation is the controlled collapse of the lung’s gas-exchange surfaces, a process known as atelectasis. At a relatively shallow depth, estimated to be around 50 meters, the immense pressure squeezes the air out of the delicate, collapsible alveoli. This air is then shunted, or forced, into the rigid, heavily reinforced airways, such as the trachea and bronchi.
These larger airways possess thick, cartilaginous walls that resist compression and do not allow for gas exchange. By forcing the air out of the alveoli and into these non-exchange zones, the whale effectively stops the uptake of nitrogen into the bloodstream. Nitrogen, which is inert and causes the bends when it forms bubbles upon rapid ascent, is prevented from dissolving under high pressure.
The whale dives on a single breath. Once the alveoli collapse, the only nitrogen available to be absorbed into the tissues is the amount already present in the bloodstream at the beginning of the dive. This mechanism ensures that the volume of nitrogen remains constant, minimizing the risk of forming bubbles as the whale ascends.