The mature respiratory tract is composed of the nasal
cavity, nasopharynx, larynx, the tubular conducting
airways including trachea, intra- and extrapulmonary
bronchi, bronchioles, and the gas exchange system
including terminal bronchioles and alveoli where gas
exchange occurs. The lungs and chest cavity are covered
in a thin, translucent pleural membrane.
There are two separate blood-conducting systems in
the lungs. The pulmonary artery system supplies venous
blood from the right ventricle to the capillary plexus
surrounding the pulmonary alveoli. The intimate association