Lecture 11 Flashcards Preview

Pharm202 > Lecture 11 > Flashcards

Flashcards in Lecture 11 Deck (16)
Loading flashcards...

What is diffusion?

Process where a concentration difference between regions is minimised as a result of spontaneous flow of matter.
Also regarded as the mass transfer of individual molecules due to random motion as a result of the concentration gradient between the two regions.


What is the driving force of diffusion?

concentration gradient


Why can diffusion be seen in gas, liquid, and dissolved solutes?

These all have a spontaneous tendency to distribute itself uniformly over the space available.


What do drug absoprtion, elmination, nutrient transport in living tissues and biological membranes all require in order to take place?



What is a membrane?

Physical barrier/film which separates two distinct compartments where the material passes through either by passive, active of facilitated transport.


what are the 3 types of membranes?

Membrane of dense material with straight through pores. Found in filter barriers like nucleopore

Homogenous membrane without pores

Cellulose membrane used in filtration showing intertwining nature of fibres and tortuous channels


what is a semi permeable membrane?

membrane which is permeable to only certain molecules and not all.


What is a barrier?

Region/(s) of a system that creates resistance to mass transfer or diffusion,
E.g. Stirring to help dissolve the salt in a cup of water.


What is the importance of fick's law?

Can describe a diffusion process


What are the criteria of fick's law?

concentration gradient doesn't change with time or distance
This is also known as diffusion under a steady state.
Fick's first law can describe the diffusion process in this situation.


What is flux proportional to? (in fick's first law)

the concentration gradient


what is flux?

the amount of material transferred through per unit cross section area in unit time

units = gcm-2sec-1 or molcm-2sec-1


Is flux a positive or negative value?

Flux is always a positive value
The negative sign only tells use that the flux is in the direction of the decreasing concentration (diffusion is movement of particles from an area of high concentration to an area of low concentration)


What is the diffusion coefficient (D) affected by?

temperature, pressure, chemical nature of solute, solvent properties

it doesnt normally remain constant


What happens in a non-steady state of diffusion?

in many systems, concentration varies with both time and distance so we cannot apply fick's first law as it is an unsteady state

we can apply fick's second law


what is fick's second law?

the change of the concentration gradient is proportional t the rate of concentration change ina volume element within the diffusion field

IF the rate of change of concentration = 0 then fick's first law can be used to describe non steady state conditions