The principal function of the respiratory system is supply the body’s living cells with oxygen, and remove carbon dioxide. The process of respiration involves four distinct steps:

• Pulmonary Ventilation - the action of breathing moves air into and out of the lungs in a continuous flow;
• External Respiration - gas exchange between the blood and the gas-filled chambers of the lungs;
• Transport of Respiratory Gases - between the site of gas exchange in the lungs and the respiring tissues of the body. This transport is achieved by the blood flowing through the cardiovascular system.
• Internal Respiration - gas exchange between the blood and the respiring tissues

The close coupling of the respiratory system with the cardiovascular system is essential for efficient and effective gas exchange. Because the respiratory system is involved with generating air flow, it also plays a role in speech and the sense of smell.

The respiratory system can be divided into two functional portions, the conducting zone and the respiratory zone. The conducting zone is composed of all the passageways which provide a route for air to pass between the external environment and the respiratory zone, which is the site of gas exchange in the lungs.

As part of the Physiome Project, the Pulmonary Research Group at the Bioengineering Institute is developing an integrated anatomically- and biophysically- based mathematical model of the pulmonary system. This model spans a range of spatial and temporal scales, from the level of the protein and cell, to the whole organ, and ultimately to integration with other organ systems in the Auckland Bioengineering Institute's virtual human.

The inability of scientists to directly assess lung tissue damage or response to drug therapy means that an integrated mathematical model that links experimental cellular measurements to whole-organ function has the potential to provide a means of evaluating the appropriateness and effectiveness of drug treatments in lung disease. The pulmonary models are developed within the framework of the Lung Physiome project.