Comp cells, volume, membrane pot, transporter

Question 1

channels with gates are controlled by what 5 forces? Provide examples

Answer 1

1. electric field (membrane pot)
2. voltage gated (ie. depolarization)
   
   • Na/K+
3. mechanical stimulation (stretching of membrane)
   
   • ie: hair cells in cochlea, touch receptors in skin
4. chemical
   
   • synaptic rcptr for nt
5. Temperature
   
   • cutaneous thermal rcptr

Question 2

Ultimately, secondary active transport depends on what?

Answer 2

Metabolism

E is released when Na+ leaks into the cells, captured, and used to pump another ion across membrane.

Question 3

As opposed to thinking of osmosis as pressure, what is a better way of thinking of it?

Answer 3

Suction.

Question 4

The quantitative relationship between osmotic suction and pressure one has to exert in order to balance it is proportional to what?

Answer 4

proportional to the difference in solute [ ] on the two sides of the (semi-permeable) membrane

Question 5

What is the quantitative proportional difference in solute [ ] on two sides of a semi-permeable membrane expressed as?

Answer 5

π=RTΔC

R=gas constant = 8.314J/k mol
or 0.08206 Latm/molK

Question 6

osmolarity

Answer 6

total [ ] solute particles

Extracellularly vs Intracellularly

Question 7

tonicity

Answer 7

cell volume (shrink/burst) after diffusion

Question 8

How do permeating solutes contribute to controlling equilibrium volume of the cell?

Answer 8

it doesn’t.
permeating solutes contributed nothing to controlling equilibrium volume of cell.
(pg 4, noon cell volume).

All that matters is the concentration of nonpermeating solutes which affects movement of water.

Question 9

a consequence of a permeating solute is that it will/will not exert as large an osmotic force as a nonpermeating solute at the same [ ]

Answer 9

will not

how much the osmotic pressure is diminished
depends on how easily the molecule can cross the membrane.

Question 10

how much the osmotic pressure is diminished

depends on what?

Answer 10

depends on how easily the permeating solute can cross the membrane.

no osmotic potential: if solute and water cross membranes with equal ease.

half the osmotic pressure: a solute crosses membrane half as easily as water

Question 11

what is reflection coefficient? its range?

Answer 11

Its a measure of how well the membrane ‘reflects’ the solute
ranges from 0 to 1(non permeating solute)

Question 12

Are solutes in the ECF permeating/nonpermeating?

Answer 12

Nonpermeating (otherwise cells would lyse)

Question 13

principle of electrical neutrality

Answer 13

bulk solutions (inside and out) have to be electrically neutral
and
[cations]i=[anions]i
[cations]o=[anions]o
total [inside]=[outside]

Question 14

Na pump properties

Answer 14

1. pump is really obligatory coupled Na/K exchange pump
2. saturable: demonstrates max rate of activity
   (carrier pump, not flux)
3. pump is electrogenic, not electroneutral, not a 1:1 pump (2 K in, 3 NA out)
4. Na/K pump never opened at same time
   (channel with 2 gates)
5. consists of 1 alpha and 1 beta subunit

Question 15

Na/K pump cycle

Answer 15

1. both outside and inner gates are close
   
   • 2 K+ ions inside
2. ATP binds, inner gates open, affinity changes from K+ to Na+.
   
   • K+ leaves and Na+ enters.
3. ATP is split. leaving pump phosphorylated, and inner gates close
4. Outer gate spontaneously opens and affinity changes from Na+ to K+
   
   • Na+ leaves and K enters
5. Pump loses its phospate, outer gate closes

Question 16

describe state of equilibrium

Answer 16

state in which no E is required to move ions across membrane to maintain state

Vm=Eion

(even if [ ] are not same on each side, for every ion in, another will leave w/o ATP)

Question 17

Diff between equilibrium and steady state

Answer 17

steady state: like equilibrium - ion concentrations arent changing over time, but requires constant input of E (ATP)

Question 18

Membrane potential depends on relative/absolute permeabilities to ions

Answer 18

relative

Question 19

What are the differences in Vm between diff cells due to?

Answer 19

1. relative permeability of K and Na
2. ion concentration
   
   • a small change in K [ ] has a big effect on Ek

Question 20

What is the driving F of an ion?

Answer 20

the difference between membrane potentials (Vm) and equilibrium potential of that ion (E)

aka the extent to which an ion wants to enter cell
V=IR or I=VG
V is driving force, G is conductance

Question 21

When Vm=ENa, what is the driving F on sodium?

Answer 21

zero

Question 22

What is Goldmans equation?

Answer 22

Vm=60log ( [K]o+P[Na]o )
———————
[K]i+P[Na]i

Question 23

External Na has large/small effects on membrane potential nerves.
External K has large/small effects on membrane potentials in nerves

Answer 23

Na: small

K: large
- nerve and muscle cells are much more permeable to K than other ions

Question 24

Hyperkalemia

1. source of extra potassium
2. Important signs
3. Strategy 4 treatment

Answer 24

1. ICF (98% of all K)
2. Compromised Kidney, cardiac arrythmia by EKG
3. CBIGK

Question 25

CBIGK

Answer 25

treatment of acute hyperkalemia in order

C: Calcium: relieve cardiac arrythmias
B: Bicarb: encourages reuptake of K
I+G: Insulin and glucose: juices/fires up Na/K pump
K: kayexalate: ion exchanger with high affinity for potassium.
Kayexalate exchanges Na for K -> removed

Question 26

Typical volume values for:
Plasma
ECF
ICF
Third space

Answer 26

Plasma: 3L
ECF: 13L
ICF: 27L
Third space: 5L