Just like most mammals, rabbits inhale oxygen through their respiratory tract, which is then delivered via the air sacs in the lungs and red blood cells to complete the body's metabolic processes. A rabbit's lungs are a pair of sponge-like organs, with the left lung divided into two lobes and the right lung into four lobes.
If the porous lung structure were fully stretched out, its surface area would be 50 to 100 times larger than the surface area of the rabbit's entire skin. The flow of air in and out of the lungs depends on the expansion and contraction of the lungs. However, because the lungs themselves lack muscular tissue, their expansion and contraction rely on the enlargement and reduction of the chest cavity.
The chest cavity expands and contracts partly through changes in the position of the ribs, with assistance from the diaphragm's movement. The diaphragm, unique to mammals, is a dome-shaped muscular membrane. Usually, chest expansion occurs due to the downward movement of the diaphragm (diaphragm muscle contraction) combined with the upward lift of the ribs (external intercostal muscle contraction). Chest contraction happens when the diaphragm rises (diaphragm relaxation) and the ribs are pulled down (internal intercostal muscle contraction).
Mammals possess a fully double-circulatory system, with the heart divided into two atria and two ventricles. Blood flows from the left ventricle into the aorta, circulates throughout the body, and returns via veins to the right atrium, completing one circulation known as the systemic circulation. Venous blood flows out from the right ventricle through the pulmonary artery into the lungs, where gas exchange occurs in the alveolar capillaries. Carbon dioxide is expelled, oxygen is absorbed, and the blood becomes arterial before returning to the left atrium via the pulmonary veins—this loop is called the pulmonary circulation.
Normal rabbit breathing is primarily through the nose. The nose has sensitive touch and olfactory cells helping rabbits detect various odor signals in the air. This mainly helps identify whether companions or potential predators are present. When rabbits detect unpleasant or alarming smells, they may stomp their hind legs to protest or run away.
Since rabbits are naturally nasal breathers, open-mouth breathing in a domestic rabbit indicates a severe situation, such as a serious respiratory infection, insufficient hemoglobin, or inability to intake oxygen. Immediate veterinary attention is necessary, and oxygen therapy (oxygen maintenance chamber) might be required to sustain life.
