What are the main areas of absorption for gases and vapours?
The main areas for absorption for gases and vapours with a high water solubility are the nasopharyngeal, which ranges from the nose to the pharynx and larynx, and the lower respiratory tract. Molecules with a low water solubility diffuse into the bloodstream through the pulmonary alveoli. This method is extremely efficient because the alveoli have a large surface area, approximately 100 m2 in humans, increasing the total area for simple/passive diffusion to take place. The distance for simple diffusion is only 0.8 micrometres meaning that there is a small distance for the substance to move across, increasing the rate at which the xenobiotics diffuse from the alveoli and the blood vessel and the overall efficiency of gaseous exchange. The constant circulation of blood there is constant maintenance of the concentration gradient which is crucial to the diffusion of oxygen and carbon dioxide, however, this also means that the xenobiotic will also have a constant negative concentration gradient. Therefore the xenobiotic will continue to diffuse into the bloodstream, increasing the dosage of the xenobiotic given to the organism leading to an increase in the adverse effects experienced by the organisms and reducing the benefits a small dosage may bring.