<P> The gastrointestinal tract is lined with epithelial cells . Drugs must pass or permeate through these cells in order to be absorbed into the circulatory system . One particular cellular barrier that may prevent absorption of a given drug is the cell membrane . Cell membranes are essentially lipid bilayers which form a semipermeable membrane . Pure lipid bilayers are generally permeable only to small , uncharged solutes . Hence , whether or not a molecule is ionized will affect its absorption , since ionic molecules are charged . Solubility favors charged species , and permeability favors neutral species . Some molecules have special exchange proteins and channels to facilitate movement from the lumen into the circulation . </P>
<P> The gastrointestinal tract is lined with epithelial cells . Drugs must pass or permeate through these cells in order to be absorbed into the circulatory system . One particular cellular barrier that may prevent absorption of a given drug is the cell membrane . Cell membranes are essentially lipid bilayers which form a semipermeable membrane . Pure lipid bilayers are generally permeable only to small , uncharged solutes . Hence , whether or not a molecule is ionized will affect its absorption , since ionic molecules are charged . Solubility favors charged species , and permeability favors neutral species . Some molecules have special exchange proteins and channels to facilitate movement from the lumen into the circulation . </P>
where does the majority of drug absorption occur
where does the majority of drug absorption occur
gastrointestinal tract
gastrointestinal tract