Lead

Environmental Toxicology

Name

Env/410

June 30, 2012

Professor

Environmental Toxicology

Toxico-kinetics is the study of the rate a toxicant enters the human body and what occurs to it after it has entered the body. Alternatively, the study of the processes used by a toxicant to create exclusive cellular impacts within an organism is called Toxico-dynamics. Toxico-kinetics consists of five steps, absorption, distribution, storage, biotransformation, and elimination (Hodgson, 2010). From these five steps there are four specific routes of toxicant exposure; injection, ingestions, absorption, and inhalation (Hodgson, 2010). From these routes there are four primary pathways of distribution; intercellular, trans-follicular, trans-cellular and sweat pores.

Toxicants move across the cell wall in one of two ways; passive transfer or facilitated transfer. The most common and simple of the two is the passive transfer. In passive transfer only two factors determine the transfer rate (Norbert, 2009). The first factor is the concentration differences between the two sides of the membrane. When one side is higher in concentration diffusion occurs until equal concentrations can be found on both sides. The second factor has to do with a substances ability to move through the small pores of the membrane or the lipophilic interior. The completion of passive transfer depends heavily on the lipid solubility, degree of ionization, and molecular size (Norbert, 2009).

Water-soluble molecules that are smaller in size can pass through the aqueous pores of the membrane. The larger of these molecules are not as transferable but some may diffuse slowly through the lipid section of the membrane (Norbert, 2009). The chemicals that have the most trouble with this process are those high in ionization. Facilitated diffusion on the other hand does not require energy, though it follows the same concentration gradient as passive diffusion. As a...