Cell

Question 1

Homeostasis controlls

Answer 1

Sensor
Integrator/comparator
Effector
Controlled variable
Set point

Question 2

Fick’s Law

Answer 2

• Rate at which molecules move from one compartment to another is dependent upon the concentration difference between the compartments

J = [DA(C1 - C2)] / X

J= water flow
D=diffusion coefficient
A= Area
C=chemical gradient (force) in compartments
X= Diffusion distance

(negative diffusion coefficient as diffusion takes place down concentration gradients.)

Flux vs force

Question 3

Simple diffusion

Answer 3

= Permeability coefficient x Area x difference in concentration

Question 4

Permeability coefficient

Answer 4

= (Partition coefficient x diffusion coefficient / thickness)

when permeability = 0 you need pores, channels, &/or transporters to move a substance across a barrier

Question 5

Partition coefficient

Answer 5

the ratio of the amounts of a substance distributed between two immiscible phases

> 1 more in membrane
<1 more in compartments

Question 6

Henry’s Law

Answer 6

Dissolved gas = solubility coeff. x Partial pressure of gas

Question 7

Osmotic pressure

Answer 7

= Gas constant x Temperature x Molality (difference in osmolality between 2 compartments.

Question 8

Water flux

Answer 8

= water permeability x Area x sigma **(refl. coef) x osmotic gradient

Water movement is governed by solute consentration

**Each substance has a reflection coefficient
i.e. how easily it is reflected by the membrane
0=not reflected, 1= fully reflected

Question 9

Hydro-static pressure

Answer 9

the difference in height in columns of water. can be overcome by adding pressure to one side equal to the hydrostatic pressure.

Question 10

Hypotonic solution

Answer 10

Increased water compared to solute.

RBC placed within will swell

Question 11

Hypertonic solution

Answer 11

Increased solute compared to water (more concentrated)

RBC placed within will shrink

Question 12

Nernst Equation

Answer 12

Electrochemical gradient

E= -(RT/zF)log (Xi/Xo)

z=valancy
T=temperature
R & F constants

@29.5 deg cent

E= -60/z log (Xi/Xo)

reverse for (-) ions

Question 13

Electrochemical gradient for multiple membrane channels

Answer 13

Example for 1 Na+ and 1 K+ ion channel

V=(1Ena + 1Ek) / 2

Example for 1 Na+ and 2 K+ channels

V= (1Ena + 2Ek) / 3

Question 14

Goldman-Hodgkin-Katz equation

Answer 14

Like the Nernst equation for each species but the Vm is weighted based on the permeability of each ion species

(eg multiplied by permeability coefficient)

Question 15

Driving Force

Answer 15

Difference of membrane potential and equilibrium potentials

Question 16

Factors that can influence net flux

Answer 16

Electrical gradient
Temperature - increased = increased flux
Surface area - increase = increased flux
Mass - increased = decreased flux
Membrane permeability - increased = increased flux
Partition coefficient