L2

Question 1

we are made up of…..

Answer 1

18% protein

15% fat

7% minerals

and water
60% in men and 55% in women

Question 2

out of your total body water (TBW) what % make up intra (ICF) and extracellular fluid (ECF)

Answer 2

ICF = 66% of our TBW
ECF = 33% of our TBW

Question 3

what makes up our ECF

Answer 3

our extracellular fluid is made up of…

75% interstitial fluid (between cells)
20% plasma
5% transcellular (inside epithelial lined spaces)

Question 4

what is osmolarity

Answer 4

the concentration of a solution expressed as the total number of solute particles per litre.

Question 5

what is the range of osmolarity in your total body water

Answer 5

285-300 mOsmol/L

it is a range because it is always changing

Question 6

what is diffusion

Answer 6

the spontaneous movement of individual molecules from a region of high concentration to a region of low concentration thus making the concentration uniform

Question 7

what do we know about the rate of diffusion

Answer 7

that it is very fast over short distances (eg at the cellular level) but decreases rapidly with distance

Question 8

what is flux (J)

what does it discribe

Answer 8

it is the movement of soluble molecules

it describes the magnitude and direction of solute movement

Question 9

what is Brownian motion

Answer 9

when solute molecules move independently of solvent molecules and other solute molecules

Question 10

if you were going to plot the flux of a molecule, what would it be strongly dependent on

Answer 10

time

if you plot movement of the molecule every 30 sec the plot will look very different to if you did every hour

Question 11

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

Answer 11

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

Question 12

what law describes net diffusional flux

Answer 12

Fick’s law

Question 13

what is Fick’s law

Answer 13

that Jnet is proportional to number of moles per unit time (dn/dt)

dn/dt = -DA(dc/dx)

Question 14

what does the diffusion coefficient reflect/tell us about

Answer 14

temp
viscosity
difference in size of solute molecules

Question 15

in the fick’s law equation D, A and x are all constant, what value can they be incorporated into

Answer 15

permeability (P)

this is a experimentally determined coefficient

Question 16

what is permeability

3 points

Answer 16

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

Question 17

what is the permeability of K+

Answer 17

it is usually about 1

P K+&raquo_space; P Na+

permeability is usually a ratio

Question 18

what is fick’s law when applied to a membrane

Answer 18

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

Question 19

what is a cell membrane

how thick is it

Answer 19

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

Question 20

does permeability allow for the fact that there are different mechanisms for different solutes to cross the cell membrane

Answer 20

yes

Question 21

can solubility diffusion be described by Fricks law? why?

Answer 21

yes

because it is a pure diffusional process and the solute dissolves (partitions) into the lipid bilayer and diffuses across the membrane

Question 22

what does solubility diffusion explain

hit (about a relationship)

Answer 22

the movement of most non-electrolytes (uncharged molecules)

it also explains the relationship between lipid solubility and permeability

Question 23

how does permeability correlate with lipid solubility and size

Answer 23

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

Question 24

what is an example of how the rate of diffusion changes with size and lipid solvability

(one example each)

Answer 24

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

Question 25

does solubility diffusion account for permeability of electrolytes? why?

Answer 25

no often the permeability is much greater than predicted from their lipid solubility

Question 26

define selectivity sequences

Answer 26

p K+ >> P Na+ the permeability for a given ion can vary from cell to cell or within a cell. it can also vary with time

Question 27

what are some examples of how permeability of a cell membrane can change with time

Answer 27

during an action potential or following the effects of hormones

Question 28

temporary combination (of a solute) with a membrane protein accounts for movement of what

Answer 28

electrolytes and anomalous (not normal) non-electrolytes

Question 29

can membrane proteins be described by fick's law? why not?

Answer 29

it cannot be described by Fick's law because membrane proteins show... slectivity saturation kinetics competition between similar species inhibition

Question 30

what dramatically increases the net flux

Answer 30

membrane proteins such as channels, carryers, and active transport

Question 31

what are saturation kinetics

Answer 31

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

Question 32

do transporters usually become saturated within a physiological context

Answer 32

no because the body does not usually contain levels of the solute where the proteins would become saturated

Question 33

what is a disease where the proteins have become saturated

Answer 33

diabetes happens when the glucose channels become saturated which is how you end up with glucose in the urine

Question 34

if channels were to become saturated at, the rate of transport can be varied by what

Answer 34

varying the kinetics of the transporter and by altering the number of transporters