Figure 4.2

Diagram of PBPK model used for ingested radon (see Appendix A for details).

which, with blood flowing from the spleen and pancreas, enters the portal circulation to the liver as shown in figure 4.2. Venous blood is pumped by the right side of the heart to the pulmonary region of the lung, the "Pulmonary" compartment of figure 4.2, where radon dissolved in blood exchanges with alveolar air and is exhaled.

Ingested 222Rn is readily absorbed and appears promptly in exhaled air. The studies of ingested radon have indicated that retention in the body is somewhat greater when radon is ingested with food (Brown and Hess 1992; Hursh and others 1965). The increased retention is presumably a result of the slower transfer of foodstuffs from the stomach to the small intestine. Whereas the small intestine is the major site of absorption of most nutrients, fractional amounts of some



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