Koalas are marsupial mammals native to Australia, instantly recognizable by their stout bodies and large noses. Like all mammals, koalas are air-breathing vertebrates that rely on a sophisticated system to exchange oxygen and carbon dioxide from the atmosphere. Their respiratory mechanics must support an entirely arboreal existence while also accommodating a highly specialized, low-energy diet.
The Structure of Koala Lungs
The koala’s respiratory system follows the basic mammalian design. Air is taken in through the nose and mouth, passes through the trachea, and leads into the lungs. Within the lungs, the branching network of bronchi and bronchioles terminates in millions of tiny air sacs called alveoli, where gas exchange occurs.
The air is moved in and out primarily through the action of the muscular diaphragm, which changes the pressure within the chest cavity. A structural variation in the koala’s skeletal frame is the presence of only eleven pairs of ribs, fewer than the thirteen pairs found in many other mammal species. Despite this difference, the overall chest cavity and lung capacity are suited to their lifestyle.
The upper respiratory tract is also specialized, notably in the nasal cavity where they lack structures called “swell bodies” that regulate airflow in some other mammals. This anatomical difference does not impair their breathing efficiency. The internal lung structure is typical, featuring the necessary components for efficient oxygenation of the blood.
Respiratory Function and Low-Energy Lifestyle
The koala’s respiratory function is linked to its unusual, low-energy existence, necessitated by a diet almost exclusively composed of eucalyptus leaves. Eucalyptus provides minimal nutritional value and contains toxins that require significant energy expenditure to detoxify. To cope with this diet, koalas have evolved a profoundly low metabolic rate, measured to be about 74% of the rate predicted for a mammal of their size.
This reduced metabolic activity directly translates to a slower respiratory rate, as the body needs less oxygen to sustain its functions. Koalas conserve energy by remaining highly sedentary, spending up to 20 hours each day resting or sleeping in the fork of a tree.
The respiratory system also plays a secondary role in thermoregulation, particularly in hot Australian climates. Koalas will resort to panting when ambient temperatures rise significantly, despite their dense fur providing insulation. Panting is a method of evaporative cooling that increases the respiratory rate to move air over moist surfaces in the mouth and throat, dissipating heat and helping them maintain a stable body temperature.