Lecture 2: Diffusion

Question 1

What percentage of women is made up of water?

Answer 1

about 55%

Question 2

What percentage of men is made up of water?

Answer 2

about 60%

Question 3

What percentage of total body water is made up of ICF?

Answer 3

66%

Question 4

What is ICF and where is it?

Answer 4

intracellular fluid

this is inside cells

Question 5

What percentage of total body water is made up of ECF?

Answer 5

33%

Question 6

What is the ECF and where is it?

Answer 6

extracellular fluid

fluid not inside cells

Question 7

What are the three components of ECF and what percentage of ECF do they make up?

Answer 7

Interstitial fluid: 75% ECF
Plasma: 20%
Transcellular: 5%

Question 8

Where is interstitial fluid?

Answer 8

in between cells

Question 9

What is plasma?

Answer 9

it is a solution in blood

Question 10

Where is transcellular fluid?

Answer 10

inside the epithelial lined space

Question 11

What are the three main ions in the ECF and ICF that determine membrane potentials?

Answer 11

Na+
K+
Cl-

Question 12

What is the osmolarity of plasma (ICF)?

Answer 12

285 mOsmolL-1

Question 13

What is the osmolarity of muscle (ICF)?

Answer 13

285 mOsmolL-1

Question 14

What is the main ion in the ICF and what is its concentration?

Answer 14

K+

150 mmolL-1

Question 15

What is the main ion in the ECF and what is it’s concentration?

Answer 15

Na+

150 mmolL-1

Question 16

What is the range for osmolarity?

Answer 16

285 - 300 mOsmolL-1

Question 17

Define diffusion

Answer 17

Spontaneous movement of individual molecules from a region of high concentration to a region of low concentration

Question 18

When is the rate of diffusion very fast?

Answer 18

over very short distances

Question 19

Rate of diffusion decreases rapidly with what?

Answer 19

distance

Question 20

Solute molecules move independently of what?

Answer 20

solvent molecules and other solute molecules

Question 21

What does flux describe?

Answer 21

the magnitude and direction of solute movement

Question 22

What does the net diffusional flux result from?

Answer 22

two unidirectional fluxes

Question 23

What is flux?

Answer 23

movement of the solute molecules

Question 24

What is the net flux?

Answer 24

net combination of the flux in one direction and the flux in the other direction

Question 25

If the concentration of the two solutions is different, the net flux is positive/negative/zero?

Answer 25

positive

Question 26

If the concentration of the two solutions is the same the net flux is positive/negative/zero? What happens here?

Answer 26

zero | there is two unidirectional fluxes but they are equal and opposite

Question 27

What is Fick's Law?

Answer 27

Jnet ∝ dn/dt = -D.A (dc/dx)

Question 28

What do we simplify Fick's Law to be and why is this?

Answer 28

Jnet = PΔC This is because D, A and Δx are all constant for a given membrane and are incorporated into a single experimentally determined permeability coefficient, P

Question 29

Define permeability

Answer 29

a measure of how fast solute crosses the membrane

Question 30

Permeability is specific for what?

Answer 30

a given membrane and solute

Question 31

Permeability gives an indication of what?

Answer 31

the rate of movement (in cms-1)

Question 32

What can permeability be used to define? Give an example

Answer 32

The selectivity of a membrane. For a given cell membrane, PK >> PNa

Question 33

Permeability makes no assumptions about the mechanisms involved. What does this mean?

Answer 33

It doesn't tell you anything about how the solutes get through eg. through diffusion or through a transporter

Question 34

What is another way of writing Jnet = PΔC? What does this tell us?

Answer 34

Jnet = P (Co - Ci) | This means the steeper the concentration, the faster the rate of diffusion

Question 35

The steeper the concentration, the faster the rate of diffusion but only if..

Answer 35

the cell is permeable to that solute

Question 36

How is permeability obtained?

Answer 36

From the modification of Fick's Law: | the concentration is given by the difference in concentration inside and outside the cell

Question 37

What is the cell plasma membrane?

Answer 37

a physical and chemical barrier that separated the inside from the outside of the cell

Question 38

The plasma membrane is a __________ _________ embedded with ________

Answer 38

lipid bilayer | proteins

Question 39

In the plasma membrane, the phosphate-rich heads are on the inside/outside

Answer 39

outside

Question 40

In the plasma membrane the hydrophobic lipid tails are in the inside/outside

Answer 40

inside

Question 41

What is the plasma membrane impermeable to? What does this exclude? Why is this?

Answer 41

it is impermeable to water-soluble molecules except water because it is polar

Question 42

P allows for the fact that there are different what?

Answer 42

mechanisms for different solutes to cross cell membranes

Question 43

What does solubility diffusion refer to?

Answer 43

the movement of most non-electrolytes

Question 44

Why can solubility diffusion be described by Fick's law?

Answer 44

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

Question 45

There is a positive/negative relationship between solubility and permeability. What are the exceptions?

Answer 45

positive | water, urea

Question 46

The more lipid soluble the solutes are, the more/less permeable they are

Answer 46

more

Question 47

For solutes with similar lipid solubilities, the smaller the solute, the more/less permeable the solute`

Answer 47

more

Question 48

Permeability correlates with size. The smaller the molecule the faster/slower the rate of diffusion

Answer 48

faster

Question 49

Permeability correlates with lipid solubility. The more soluble the solutes, the more/less permeable they are

Answer 49

more

Question 50

What is interesting about adding acetates to molecules and their fat solubility?

Answer 50

adding more acetate increases fat solubility although it increases the size

Question 51

Solubility diffusion does not account for what?

Answer 51

Permeability of electrolytes. Often the permeability is much greater than predicted from their lipid solubility

Question 52

What can the permeability for a given ion vary from and with?

Answer 52

it can vary from time to time and can vary with time

Question 53

What does the temporary combination with membrane proteins account for?

Answer 53

the movements of electrolytes and anomalous non-electrolytes

Question 54

Why is combination with membrane proteins is not described by Fick's law?

Answer 54

because it shows - selectivity - saturation kinetics - competition between similar species - inhibition

Question 55

Even though protein mediated transport is not described by Fick's law, __________ is still a useful measure

Answer 55

permeability

Question 56

What does protein-mediated transport mean?

Answer 56

transport aided by proteins such as channels and transporters

Question 57

Transporters may not be saturated over what?

Answer 57

physiological concentration range

Question 58

Even when saturated at physiological concentrations, the rate of transport can be varied by what two things?

Answer 58

- varying kinetics of transporter | - altering the number of transporters

Question 59

As the ΔC or driving force increases, what happens to Jnet?

Answer 59

it increases at a decreasing rate and then levels off as the transporters become saturated

Question 60

At low concentrations, there is a smaller/larger influx

Answer 60

larger