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Table 2 Characteristic Cell Numbers and Lung Values

From: Scope and relevance of a pulmonary biopharmaceutical classification system AAPS/FDA/USP Workshop March 16-17th, 2015 in Baltimore, MD

Parameter Value Unit Reference
Alveolar Surface Area 143 m2 (Gehr et al. 1978)
# of alveoli (adult lung) 250+ Million (Crapo et al. 1982)
# of type I pneumocytes 1.9 Billion (Crapo et al. 1982)
# of type II pneumocytes 3.7 Billion (Crapo et al. 1982)
# of resident macrophages 2.3 Billion (Crapo et al. 1982)
Depth of airway fluid 5–10 um (Widdicombe 2002)
Harmonic mean depth of alveolar fluid 0.2 um (Bastacky et al. 1995)
Diameter of an alveolus 200–250 um (Parent 1982)