Derek S. Wheeler, Hector R. Wong, and Thomas P. Shanley (Eds.)

2009

The principal role of the respiratory system is to permit effi cient exchange of respiratory gases (O2 and CO2) with the environment. The respiratory system is unique in that it is constantly exposed to a barrage of foreign substances from both the internal environment (at any one point in time, approximately one-half of the cardiac output is received by the lungs) and the external environment (with each breath, the respiratory tract is exposed to pollens, viruses, bacteria, smoke, etc).