PRINCIPLES OF TOXICOLOGY

178 PULMONOTOXICITY: TOXIC EFFECTS IN THE LUNG
Figure 9.9 Scanning electron micrograph of the interior of an alveolus showing pores of Kohn (P) and a
macrophage (arrow). [Reproduced with permission from Murray (1976) (see Figure 9.4 source note).]
rupture and spill the proteolytic enzymes into the lung tissues and damage them. If successful
phagocytosis has occurred, the phagocytized material is then removed by either the mucociliary
escalator or by lymphatic drainage. The action by the macrophages is initially very rapid, with inhaled
particles engulfed by some macrophages within minutes of inhalation.
Gases and Vapors
Many injuries to the lung and to distant organs have been known to occur following inhalation exposure
to gases and vapors, especially in the workplace. Most industrial chemicals can exist in the gas or vapor
state under certain situations, and various industrial processes can create even the fairly extreme
physicochemical conditions necessary to vaporize potentially toxic agents. Everyday in the workplace,
millions of workers are exposed to countless potentially toxic chemicals in the form of gases and
vapors.
The potential for highly toxic outcomes from inhalation exposures to gases and vapors is related
to the fact that once they are inhaled into the lung, they can pass directly into the bloodstream. In a
pharmacokinetic sense, inhaled gases and vapors are injected into the bloodstream as a patient would
receive a drug through an intravenous (or intraarterial) infusion. Once a gaseous chemical enters the
alveolar spaces of the lung, it can cross the relatively permeable alveocapillary membrane complex
and enter the pulmonary blood. This complex consists primarily of the capillary and alveolar
membranes, separated by an interstitial space (sometimes with fluid in it). The lining of the alveolar
membrane also has a lining of surfactant (dipalmitoyl lecithin), which serves to equalize the inflation
pressures of the heterogeneously sized alveolar sacs.
The passage of the inhaled gases and vapors across the alveocapillary membrane complex, or the
diffusion efficiency, is influenced by several factors. The solubility of the inhaled compound is
important, as highly water-soluble compounds are often more likely to deposit in the upper respiratory