How does blood distribute toxic chemicals throughout the body?

Once a toxic substance enters the body and crosses a transport barrier, it is distributed throughout the body via the bloodstream. The efficiency and speed of this distribution are influenced by several key factors:12

• Capillary Permeability: Chemicals move from the blood into tissues by crossing capillary walls. The structure of these walls varies: tight capillaries (such as those in the blood–brain barrier) restrict the passage of large or hydrophilic molecules, while continuous, fenestrated, and discontinuous capillaries allow varying degrees of diffusion for smaller molecules.1
• Protein Binding: Many chemicals bind to plasma proteins like albumin. Because these proteins are too large to exit the bloodstream, bound chemicals remain confined to the blood, which limits their distribution to tissues.3
• Tissue Blood Flow: The rate of accumulation in specific tissues depends on how well they are perfused. Well-perfused organs, such as the liver, brain, and kidney, reach a steady state with blood concentrations rapidly, whereas poorly perfused tissues like fat and bone accumulate chemicals more slowly.4

Ultimately, once in the interstitial spaces, chemicals move into cells via diffusion or active transport.1