NCIt definition : The part of the respiratory system below the bifurcation of the trachea. It includes
the lungs and the parts of the lungs such as the bronchioles and alveoli.;
Alternative definition : CDISC: The part of the respiratory system below the bifurcation of the trachea. It
includes the lungs and the parts of the lungs such as the bronchi, bronchioles and
alveoli.;