Diffusion, permeability, ionic gradients Flashcards
Describe Fick’s First Law of Diffusion. What is flux and how does it change with concentration gradient?
Explain the significance of the negative sign in Fick’s diffusion law.
Describe the relationship between the diffusion distance of a molecule and time taken to diffuse. If the distance d travelled by a molecule is 100um and the diffusion coefficient is 500um2, how would you find the time taken to diffuse over 100um?
What is the significance of the partition coefficient and what is its effect on flux and the concentration gradient?
The partition coefficient makes up for the differences in solubility depending on where one is in relation to the cell membrane.
Describe the permeability coefficient
A cell’s permeability coefficient is a measure of a membranes permeability for a solute.
Describe influx vs efflux in the context of permeability and Fick’s diffusion law
Influx: things on the outside of the cell coming in
Efflux: things on the inside of the cell exiting out
Using a drawing, illustrate the difference between hydrostatic pressure and osmotic pressure
How do you calculate osmotic pressure in an ideal situation, and taking the reflection coefficient into account? What is the significance of the reflection coefficient?
The reflection coefficient is a measure of whether or not a solute will pass through a semi-permeable membrane.
Describe the relationship between hydrostatic pressure and osmotic pressure (i.e. describe the Starling equation)
Using a drawing, describe fluid flow in the capillaries. How do the values of interstitial and capillary hydrostatic and osmotic pressure change, if at all?
Describe fluid flow along a capillary (i.e. what are the differences in interstitial vs capillary hydrostatic and osmotic pressures as you move closer to arterioles vs venules?)
Describe the effect of adding a permeant solute on the volume of a cell. True/False: Only permeant solutes cause permanent changes in volume.
False. Only impermeant solutes can cause permanent changes to cell volume
Describe the effect of adding or decreasing the concentration of an impermeant solute on the volume of a cell
** only an impermeant solute causes permanent changes in volume **
How do you estimate a cell’s volume when you change the extracellular concentration of an impermeable solute?
What is the definition of equilibrium?
For a cell that has a high intracellular K+ concentration, low intracellular Na+ and Cl- concs and is only permeable to K+, describe how you would reach equilibrium? (i.e what is the role of the K+ concentration gradient and the electrochemical gradient?)
Write out the equation you would use to find an ion’s equilibrium potential.
No net flow of current or ions so there is no flux
(see diagram)
Nernst equation (Eq = RT/zF * ln [Ion]o/[Ion]i]
What does the GHK equation describe?
What is the one factor you consider with the GHK that you don’t include when calculating the Nernst?
How can you arrive at a scenario in which the GHK reduces down to the Nernst? Write out the equation and explain.
GHK describes resting membrane potential (mebrane potential at steady state when there’s no net flow of electrical charge in/out of cell)
Membrane permeability for the ion(s) in question
In a cell where you have multiple ions and various permabilities to those ions, the permeability of the membrane to one particular ion has to be high enough such that the permeabilities to the other ions are negligible and thus cancel out in the equation.
Vm = RT/F * ln Pion a[A]o + Pion b[B]o + Pion c[C]/Pion[A]i + Pionb[B]i + Pion c[C]i
What is the definition of current?
Explain the direction of current and flux based on the scenarios below:
Positive charge leaving cell
Negative charge leaving cell
Negative charge entering cell
Positive charge entering cell
Define driving force. What are the implications if:
Drviving force is greater than zero
Driving force is less than zero
Driving force equal to zero
Describe the Donnan effect
