Living in a watery environment, whales and other cetaceans require certain adaptations in order to survive. Whales are mammals, breathing fresh air by means of a blowhole and a pair of lungs. The basic mechanics of whale respiration are similar to those of human beings.
Whales need to emerge from the water, exposing the blowhole on the tops of their heads completely, in order to take a fresh breath. As they surface, they expel the carbon dioxide-rich air in their lungs in a strong exhalation, the vapour of which often causes a misty blow that helps experts to identify different species from a distance. They then fill their lungs with fresh air before diving beneath the surface of the water again
Fin Whale breathing on the surface.
However, the problem with this type of respiration is that large lungs full of air would hinder the whale’s ability to dive to any significant depths. These organs would act like floats or balloons. Therefore, the relative size of the lung is actually quite small in proportion to its body, and the amount of air they contain is not quite as much as may be expected.
Boyle’s Law states that gases in direct contact with liquids will likely dissolve (even if only partly) in the liquid. A state of stability is eventually achieved in which the liquid has become saturated with the gas. If the pressure on the gas increases, more of it will dissolve in the fluid. The nitrogen in the body tissues of the whale needs to remain dissolved so that it does not become converted back into a gas and affect the whale physically, causing decompression illness. Having a flexible ribcage plays an integral role in maintaining optimal pressure by collapsing under the heavy weight of the water as the animal descends deeper and deeper beneath the ocean’s surface. With minimal air left in the lungs, nitrogen cannot dissolve into the body tissues. Soon, the lungs actually collapse, being almost emptied of gaseous oxygen.
When this happens, gaseous exchange occurs at an alveolar level so that the last remaining bit of air is pushed into the bronchioles, after which the alveolar sacs collapse. The bronchioles are cartilaginous, which prevents a gas exchange with the body.
To preserve the level of oxygen in their system after this collapse of lungs, cetaceans are able to store about half of their oxygen in their muscles, rather than just in their lungs. This is due to the high level of haemoglobin and myoglobin in whales. These proteins have the primary function of carrying oxygen in the blood and muscles, respectively.
Whales are also able to control the assignment of blood to various parts of their body. So, when diving to great depths, they allow only the vital organs to receive oxygen-rich blood. Areas that are not as important to the whale’s survival are cut off from the blood supply temporarily. Circulation to these areas is re-initiated when the whale surfaces.
Bradycardia is a reflex that causes the whale’s pulse to slow down dramatically as it dives. A slower pulse means that less oxygen is required.