Passive Diffusion
Passive Diffusion - Related Videos
01:17
Passive Diffusion: Overview and Kinetics
0 Views •
2024
Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness. When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting their diffusion into...
08:01
The Diffusion of Passive Tracers in Laminar Shear Flow
0 Views •
Cited by 4 •
2018
A protocol for the study of the diffusion of passive tracers in laminar pressure-driven flow is presented. The procedure is applicable to various capillary pipe geometries.
03:31
Diffusion and Osmosis - Concepts
0 Views •
2019
Cell Membranes and Diffusion In order to function, cells are required to move materials in and out of their cytoplasm via their cell membranes. These membranes are semipermeable, meaning that certain molecules are allowed to pass through, but not others. This movement of molecules is mediated by the phospholipid bilayer and its embedded proteins, some of which act as transport channels for molecules that otherwise would not be able to pass through the membrane, such as ions and carbohydrates.
08:18
Diffusion and Osmosis - Student Protocol
0 Views •
2019
Diffusion in Agar ExpandNOTE: In this exercise, you will be given agar containing an indicator chemical called phenolphthalein. When phenolphthalein is exposed to the normal alkaline conditions in the agar, it will look pink. But when it is exposed to neutral or acidic conditions, it changes from pink to clear. You will make different size and shaped agar cubes as a model for cells to study the impact of cell size and shape on diffusion rate. To make the first set of cells, measure out and cut...
02:55
Diffusion and Osmosis - Instructor Prep
0 Views •
2019
Preparation of Solutions for the Agar Cube Experiment ExpandIMPORTANT: Wear gloves, goggles, and appropriate personal protective equipment – chemicals can be hazardous at high concentrations. For the diffusion indicator solution, weigh out 1 g of phenolphthalein and add it to a beaker containing 100 mL of 95% ethanol. To make the basic solution for the agar, measure 80 mL of water into a beaker, and then add 0.4 g of NaOH. Stir until the solute is dissolved then bring the total volume of the...
FAQs
Ionization determines how much of a drug remains in the uncharged form available to enter a lipid bilayer. Because the uncharged, lipid-soluble fraction generally crosses more readily, changes in ionization can alter membrane passage even when the total drug concentration remains similar. This helps explain differences in permeability.
Membrane surface area and thickness influence the rate of passive diffusion. A larger area provides more membrane through which molecules can pass, whereas a thicker barrier presents a longer path. These structural factors work alongside the concentration gradient and drug properties, so two membranes may produce different passage rates.
Passive diffusion differs from transport that depends on a protein or cellular energy because its progress is governed primarily by the gradient and membrane compatibility of the molecule. Consequently, the method reflects the drug’s own physicochemical properties rather than a specified carrier’s activity, making lipid partitioning and ionization central considerations.
During gastrointestinal absorption, passive diffusion can determine how efficiently a drug crosses into the body. Molecules that partition into the lipid membrane and maintain a favorable concentration gradient are more likely to pass. The resulting permeability contributes to bioavailability and helps explain why physicochemical properties matter when evaluating drug absorption.
After entering the circulation, membrane passage can affect distribution into tissues and access to cellular targets. A drug’s concentration gradient, ionization state, and ability to partition into lipid bilayers influence whether it can move from one compartment to another. Thus, passive diffusion links membrane permeability with the extent and location of pharmacological exposure.
Pharmacologists can use passive diffusion principles to interpret permeability and anticipate bioavailability from a drug’s physicochemical profile. The analysis considers whether the molecule is sufficiently lipid-soluble, what fraction is uncharged, and whether the relevant membrane offers adequate area and limited thickness. These considerations support predictions about absorption and tissue access.