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BMS 752 (Medical Physiology) > Membrane transport > Flashcards

Membrane transport Flashcards

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USMLE® Step 1 flashcards
1
Q

what are three methods of solute transport across cell membranes

A
  1. passive/non-carrier mediated
  2. passive/carrier mediated
  3. active
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2
Q

three examples of passive non carrier cell transport

A
  1. simple diffusion across the cell membrane
  2. simple diffusion through pores
  3. simple diffusion through gated channels
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3
Q

what is an example of carrier mediated transport

A

facilitated diffusion

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4
Q

what are three methods of active solute transpoirt

A
  1. active transport requiring ATP
  2. active transport using energy from redox reactions
  3. secondary active transport
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5
Q

osmosis

A

the diffusion of water across a cell membrane

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6
Q

what happens in secondary active transport

A

two simultaneous movement of two link substances across a cell membrane

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7
Q

two types of secondary active transport

A
  1. symport
  2. antiport
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8
Q

symport

A

coupled transport where the linked substances move in the same direction

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9
Q

antiport

A

coupled transport where the two substances move in opposite directions

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10
Q

what types of solutes are capable of simple diffusion? examples (3)

A

solutes must be uncharged and hydrophobic

  1. gasses
  2. steroid hormones
  3. anesthetics
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11
Q

what is the driving force behind simple diffusion

A

the concentration gradient on either side of the cell membrane

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12
Q

define all variables

A

R = ideal gas constant (.002kcal/mol)

T = temp in Kelvin (310 in humans)

Xi = intracellular fluid concentration of X

X0 - extracellular fluid concentrationof X

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13
Q

flux

A

the number of moles of a solute that cross a unit area of a membrane per unit of time (moles/cm2 * s)

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14
Q

what is ficks first law of diffusion

A

flux will move from areas of high concentration to areas of low concentration

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15
Q

what two factors determine the amount of flux (diffusion)

A
  1. permeability of the membrane to X
  2. magnitude of the gradient fo X across the membrane
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16
Q

pores

A

intergra membrane proteins that for conduits that are always open

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17
Q

channell

A

a gated pore that can be opened or closed

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18
Q

describe the variables and what this equation means (3)

A
  1. the electrochemical difference is the the driving force behind passive diffusion
  2. the electrochemical difference is the sum of the chemical energy difference and electrical energy difference
  3. z = valence of the ion, F = .023kcal/mol *mV, psi1 - psi0 = the membrane potential
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19
Q

describe the variables

A
  • E si the equilibrium potential for the ion
  • R is the ideal gas constant
  • T is the temperature in kelvin
  • Xi is the ICF solute concentration
  • Xo is the ECF solute concentration
  • zx is the valence of electron x
  • F is Farraday constant
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20
Q

what are six steps in passive membrane transport through integral membrane proteins

A
  1. the carrier protein is open
  2. x enters the protein and bind to the binding site
  3. outer gate closes and x becomes trapped in the protein
  4. inner gate opens with x still bound
  5. X exits the inside of the cell
  6. the outer gate closes, occluding the empty binding site
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21
Q

primary active transport

A

solute movement against electrochemical gradiant that requires energy

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22
Q

what are two sources of energy for primary active transport

A
  1. ATP hydrolysis
  2. directly from a primary metabolic reaction
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23
Q

aquaporins

A

specialized water channels in the cell membrane

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24
Q

what are two types of cells that always have aquaporins (AQP1)

A
  1. RBCs
  2. Renal proximal convoluted tubule
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25
Q

what is an example of a cell that places aquaporins based on hormonal control

A

cells in the renal collecting duct in response to ADH

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26
Q

why is it impractical to measure the concentration of water

A

because there is too mich water to be accurate

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27
Q

what is the relationship between solute concentration and water concentration

A

as solute concentration goes up water concentration goes down

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28
Q

Gibbs-Donnan effect

A

the effect of a charged membrane on charged particles, leading to unequal distribution of ions across the membrane

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29
Q

why must animal cells perform osmotic work

A

because animal cells swell rather than increase osmotic pressure as water enters and must pump water out of the cell

30
Q

when does osmotic work occur

A

during active transport with the Na/K pump

31
Q

osmolality

A

the total number of osmotically active solutes in a solution

32
Q

tonicity

A

the comparision of effective osmolalities between two solutions seperated by a membrane

33
Q

what happens to the ECF and ICF with an infusion of isotonic saline

A

ECF increases with no increase in ICF because there is no change in osmolality

34
Q

what happens to ECF and ICF with an infustion of solute free water

A

the ECF experiences an intial decrease in osmolality, causing solutes to diffuse out of the ICF to restore equalibrium

35
Q

what happens to ECF and ICF with an infusion of NaCl

A

ECF experiences an increase in osmolality, causing solute to difuse into the ICF

36
Q

why is epithelial transport important to homeostasis

A

it controls the composition of interstitual fluid through membrane transport between the body and environment

37
Q

two places where epithelial transport takes place

A
  1. apical membrane
  2. basolateral membrane
38
Q

three parts of the apical membrane

A
  1. brush border
  2. mucosal membrane
  3. luminal membrane
39
Q

two parts of the basolateral membrane

A
  1. serosal membrane
  2. peritubular membrane
40
Q

apical membrane

A

the cell surfaces that face inward toward a lumen

41
Q

basolateral membrane

A

the epitheial cells surfaces that face adjacent cells or toward the underlying connective tissue

42
Q

two epithelial transport membrane

A
  1. transcellular
  2. paracellular
43
Q

transcellular epithelial transport

A

substances crosses the cell by going through the apical and then basolateral membranes

44
Q

paracellular epithelial transport

A

substances bypass the cell and cross epithelium through cell junctions

45
Q

two types of epithelial cell junctions

A
  1. tight
  2. leaky
46
Q

tight epithelia

A

cell junctions that maintain large ion concentration and osmotic gradients

47
Q

four examples of tight epithelia

A
  1. distal portion of the distal convoluted tubule
  2. collecting duct
  3. large intestine
  4. urinary bladder
48
Q

leaky epithelia

A

cell junctions cannot maintain large gradients and are used for bulk transport of solute and water

49
Q

two examples of leaky epithelia

A
  1. small intestine
  2. proximal convoluted tubule
50
Q

where are the Na/K pumps located

A

the basolateral membrane

51
Q

what is the function of the Na/K pumps

A

the keep a large inward Na gradient to drive secondary active transport

52
Q

what happens to most of the K brought into the cell from the Na/K pump

A

it is recycled through the basolateral membrane via K channels

53
Q

flow

A

movement of matter

54
Q

flux

A

diffusion

55
Q

current

A

the flow of charged particles

56
Q

how can we increase current, flow, or flux

A

increase the driving force or decrease the resistance

57
Q

what is a simple way the body can regulate function

A

by regulation of current flux and flow

58
Q

T/F passive transport does not involve energy

A

false, passive transport releases energy

59
Q

in terms of energy, what direction does diffusion move

A

from high energy to low energy

60
Q

from an energy standpoint, what is a concentration gradient

A

store potential energy

61
Q

what is the largest energy expenditure in basal metabolism

A

the Na/K pump

62
Q

what is the driving force of simple diffusion

A

the chemical energy difference on each side of the concentration gradient

63
Q

resting membrane potential for a neuron

A

-70mV

64
Q

what is the charge inside the cell? why

A

negative, because the positive sodium is pumped out

65
Q

why is the resting membrane potential of a cell relevant to diffusion

A

because it is negative, so positive ions are pulled into the cell, and the concentration pushes sodium into the cell

66
Q

based on chemical energy and concentration, where will potassium be driven in the cell

A

it will depend on if the chemical energy is overcome by potential energy of the concentration gradient

67
Q

what direction does a negative delta G move

A

into the cell

68
Q

what direction does a positive delta G move

A

out of the cell

69
Q

what is the nerst equation and what is it used for

A

used to determine the equilibrium concentration of an ion

70
Q

what is used to determine the concentration gradient

A

the ideal gas law

71
Q

what is used to determine the electrochemical gradient

A
72
Q

why does a cell do osmotic work

A

to counter act donnan forces that move ions into the cell

BMS 752 (Medical Physiology) (13 decks)

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