Cell Physiology Flashcards
What is diffusion?
The spontaneous movement of individual molecules in a solution - from a region of high concentration to a region of low concentration
What is Brownians Motion?
The theory that solute molecules move independently of solvent molecules and other solute molecules
What is flux (J)?
Describes the magnitude and direction of solute movement.
Flux refers to the movement of substances across a membrane in a specific direction, taking into account both the influx and efflux of molecules. It is an important process that helps maintain the balance between the internal and external environments of cells.
What percentage of male and females bodies are water?
Men 66%
Women 55%
What percentage of the bodies water total is ICF?
66% (and 33% ECF)
What doe ECF consist of?
ISF
Plasma (solution in blood)
Transcellular (inside epithelial lined spaces)
What percentage of ECF is ISF?
75%
What percentage of ECF is plasma?
20%
What percentage of ECF is transcellular?
5%
How many mol L -1 of Na+, K+ and Cl- is in plasma ECF?
150
5
110
How many mol L -1 of Na+, K+ and Cl- is in muscle ICF?
10
150
8
What is the plasma membrane?
Physical and chemical barrier separating the inside of a cell from the outside of a cell.
What is the composition of a plasma cell membrane?
A lipid bilayer with embedded proteins that are 5-10 mm thick.
It has phosphate-rich heads on the outside and hydrophobic lipid tails on the inside.
It is soft and flexible
Lipid bilayer is impermeable to water-soluble molecules.
What does Fick’s law describe?
It describes the net diffusion flux
What are the units for Ficks law?
cm2 or m2/sec
What three factors influence the diffusion coefficient (the amount of a particular substance that diffuses across a unit area in 1 s under the influence of a gradient of one unit)?
Temperature
Viscosity of the solution
Difference in size of solute molecules
What is “P” in Ficks Law?
Permeability coefficient
it is the combination of D, A and x constants.
What does the permeability coefficient tell us?
Measures how fast solute crosses membrane
gives an indication of the rate of movement - quantifies the ease with which solutes cross the cell membrane
BUT makes no assumption about the mechanisms involved for the solutes crossing the membrane
How is the permeability coefficient worked out?
Experimentally determined
Obtained from the modification of Ficks Law
Jnet = P x change in C (which is calculated by concentration outside - concentration inside)
The steeper the concentration gradient, the faster the rate of diffusion BUT what?
But only if the cell membrane is permeable (P) to that solute (and this varies a lot).
What does solubility diffusion explain?
the movement of most non-electrolytes (uncharged solutes)
What does permeability correlate with?
Lipid solubility and size of solute
E.g.,
The more lipid soluble the solutes, the more permeable they are
The smaller the molecule (molecular weight) the faster the rate of diffusion
On a graph showing the relationship between lipid solubility and permeability what is on the Y axis and what is on the X axis (include units)?
Y axis = permeability x 10 ^7 (cm/s^-1)
X axis = solubility in lipids (oil water partition coefficient - includes methanol, ethanol, butanol, propanol and acetamide).
Will smaller solutes always have greater permeability?
Normally but not if the thing that makes them bigger make it move faster.