CELL NUMBER AND DISTRIBUTION IN HUMAN AND RAT AIRWAYS

Morphometric procedures were used to determine the number of cells, ce ll volume, cell diameter, and surface areas of the airways in human an d rat lungs. Nuclear sizes of epithelial cells from human bronchi were significantly larger than other lung cell nuclei. The average volume of human ciliated cell nuclei was 310 +/- 30 mum3 and 167 +/- 12 mum3 in bronchi and bronchioles, respectively. The smaller nuclei of human bronchioles were comparable to those of alveolar cells. In the pseudos tratified epithelium of human bronchi, basal cells had a large surface area in contact with the basement membrane (51.3 +/- 4.6 mum2 per cel l) when compared with ciliated (1.1 +/- 0.1 mum2), goblet (7.6 +/- 1.2 mum2), or other secretory cells (12.0 +/- 2.1 mum2). In the first fou r airway generations distal to the trachea, basal cells account for 30 % of the cells in human airway epithelium and 2% of the cells in rat a irway epithelium. Total airway surface area from trachea to bronchiole s was 2,471 +/- 320 and 27.2 +/- 1.7 cm2 in human and rat lungs, respe ctively. These direct measurements of airway surface area are less tha n half of the estimates based on current lung models. The total number of airway epithelial cells were 10.5 X 10(9) for human and 0.05 X 10( 9) for rat lungs. For both species, there were 18 times more alveolar cells than bronchial epithelial cells.