L2 Flashcards
we are made up of…..
18% protein
15% fat
7% minerals
and water
60% in men and 55% in women
out of your total body water (TBW) what % make up intra (ICF) and extracellular fluid (ECF)
ICF = 66% of our TBW ECF = 33% of our TBW
what makes up our ECF
our extracellular fluid is made up of…
75% interstitial fluid (between cells)
20% plasma
5% transcellular (inside epithelial lined spaces)
what is osmolarity
the concentration of a solution expressed as the total number of solute particles per litre.
what is the range of osmolarity in your total body water
285-300 mOsmol/L
it is a range because it is always changing
what is diffusion
the spontaneous movement of individual molecules from a region of high concentration to a region of low concentration thus making the concentration uniform
what do we know about the rate of diffusion
that it is very fast over short distances (eg at the cellular level) but decreases rapidly with distance
what is flux (J)
what does it discribe
it is the movement of soluble molecules
it describes the magnitude and direction of solute movement
what is Brownian motion
when solute molecules move independently of solvent molecules and other solute molecules
if you were going to plot the flux of a molecule, what would it be strongly dependent on
time
if you plot movement of the molecule every 30 sec the plot will look very different to if you did every hour
compare the net flux when the concentration of a solute is the same on both sides of a selective barrier compeered to when there is a difference in concentration
when the concentrations are different solutes will move in both directions BUT more will move from high to low therefore Jnet will not = 0
if the concentration is the same on each side the 2 unidirectional fluxes still occur but they are in equal and opposite directions. therefore Jnet = 0
what law describes net diffusional flux
Fick’s law
what is Fick’s law
that Jnet is proportional to number of moles per unit time (dn/dt)
dn/dt = -DA(dc/dx)
what does the diffusion coefficient reflect/tell us about
temp
viscosity
difference in size of solute molecules
in the fick’s law equation D, A and x are all constant, what value can they be incorporated into
permeability (P)
this is a experimentally determined coefficient
what is permeability
3 points
it is specific for a given membrane and solute which allows for the specific properties of those to be shown
it gives an interaction of the rate in which the solutes will cross the membrane (cm/s)
can be used to define the selectivity of a membrane
NOTE that it makes no assumptions about the mechanisms involved
what is the permeability of K+
it is usually about 1
P K+»_space; P Na+
permeability is usually a ratio
what is fick’s law when applied to a membrane
Jnet = P (Co - Ci)
the steeper the concentration gradient the faster the rate of diffusion BUT only is the membrane is permeable to that solute
what is a cell membrane
how thick is it
it is a physical and chemical barrier which separates the inside from the outside
it is a lipid bilayer with embedded proteins
it is about 5-10nm thick
phosphate rich heads on the outside
hydrophobic lipid tails on the inside
it is impermeable to water soluble molecules (except water because it is polar and very small)
its is soft and flexible
does permeability allow for the fact that there are different mechanisms for different solutes to cross the cell membrane
yes
can solubility diffusion be described by Fricks law? why?
yes
because it is a pure diffusional process and the solute dissolves (partitions) into the lipid bilayer and diffuses across the membrane
what does solubility diffusion explain
hit (about a relationship)
the movement of most non-electrolytes (uncharged molecules)
it also explains the relationship between lipid solubility and permeability
how does permeability correlate with lipid solubility and size
the more lipid soluable the solutes the more periable they are (homophobic vs hydrophilic)
for solutes with similar lipid solubilities the smaller the solute the more permeable it is
what is an example of how the rate of diffusion changes with size and lipid solvability
(one example each)
ethylene glycol and di-ethylene glycol have the same lipid solubility but EG has a better permeability because it is smaller
glycerol is much smaller than glycerol try-acetate BUT the acetate groups make it more lipid soluable therefore glycerol try-acetate has a better permeability
does solubility diffusion account for permeability of electrolytes? why?
no
often the permeability is much greater than predicted from their lipid solubility
define selectivity sequences
p K+»_space; P Na+
the permeability for a given ion can vary from cell to cell or within a cell. it can also vary with time
what are some examples of how permeability of a cell membrane can change with time
during an action potential or following the effects of hormones
temporary combination (of a solute) with a membrane protein accounts for movement of what
electrolytes and anomalous (not normal) non-electrolytes
can membrane proteins be described by fick’s law? why not?
it cannot be described by Fick’s law because membrane proteins show…
slectivity
saturation kinetics
competition between similar species
inhibition
what dramatically increases the net flux
membrane proteins such as channels, carryers, and active transport
what are saturation kinetics
flux at the start will be much faster and then the curve will flatten out because the membrane proteins will become saturated therefore they will not be able to go any faster as there will be none left to carry out their task
do transporters usually become saturated within a physiological context
no because the body does not usually contain levels of the solute where the proteins would become saturated
what is a disease where the proteins have become saturated
diabetes happens when the glucose channels become saturated which is how you end up with glucose in the urine
if channels were to become saturated at, the rate of transport can be varied by what
varying the kinetics of the transporter and by altering the number of transporters
