18. Why does the GI tract take longer to absorb?: The GI tract is lined with
epithelial cells; drugs must permeate through these cells in order to be absorbed
into the circulatory system.
19. What is One particular cellular barrier that may prevent absorption of a
given drug?: the cell membrane. Cell membranes are essentially lipid bilayers which
form a semipermeable membrane.Pure lipid bilayers are generally permeable only to
small and uncharged solutes, hence whether or not a molecule is ionized will affect its
absorption, since ionic molecules are charged.
20. What is solubility?: Solubility favors charged species, permeability favors neu-
tral species. Some molecules have special exchange proteins and channels to
facilitate movement from the lumen into the circulation.
21. Why does absorption occur at a slower rate for oral, IM, SQ routes?: Ab-
sorption occurs at a slower rate because the complex membrane systems of GI
mucosal layers, muscle, and skin delay drug passage.
22. The ability of a drug to cross a cell membrane depends on:: whether the drug
is water or lipid (fat) soluble.Lipid-soluble drugs easily cross through cell mem-
branes; water-soluble drugs can't. Lipid-soluble drugs can also cross the blood-brain
barrier and enter the brain.
23. As a drug travels through the body, it comes in contact with?: proteins such as
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