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South College Human Physiology > Week 1- Membrane Physiology > Flashcards

Week 1- Membrane Physiology Flashcards

1
Q

How does cell membrane structure vary throughout the body?

A

All cell membranes have a common structure (phospholipid bilayer)

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2
Q

Describe the fluidity of a cell membrane

A
  • Dynamic, fluid

- Things in the cell membrane (like proteins) can move around in the membrane

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3
Q

What percentage of proteins in an animal cell’s genome are membrane proteins?

A

30%

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4
Q

Most common type of phospholipid

A

Phosphoglycerides

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5
Q

Structure of a phospholipid

A
  • Glycerol back bone w/ attached phosphate group

- 2 hydrocarbon tails

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6
Q

What kind of bond does one of the hydrocarbon tails have?

A

cis-double bond (creates a bend)

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7
Q

What is the effect of the cis-double bond in the hydrocarbon tail?

A
  • Thinner membrane

- More fluidity (space between phospholipid)

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8
Q

How to phospholipid bilayers formed?

A

Spontaneously

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9
Q

Amphiphilic

A

One side of the bilayer is hydrophilic, the other is hydrophobic

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10
Q

What advantage does spontaneously forming the bilayer provide?

A

Provides important self-healing capability

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11
Q

Mechanisms for the cell tethering membrane proteins

A
  • Self assemble
  • Tethered to macromolecules on the outside
  • On the inside
  • On the surface of another cell
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12
Q

Why is restricting proteins to specific domains important?

A

Prevent flow of solutes in the wrong direction

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13
Q

What percentage of body weight is total body water (TBW)

A
  • 50-70%

- Inversely proportional to body fat

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14
Q

What are the divisions of total body water (TBW)?

A
  • Intracellular fluid (ICF)

- Extracellular fluid (ECF)

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15
Q

How much of TBW is intracellular fluid (ICF)?

A

ICF = 2/3 TBW

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16
Q

How much of TBW is extracellular fluid?

A

ECF = 1/3 TBS

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17
Q

Extracellular fluid is made of what?

A
  • Interstitial fluid

- Plasma

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18
Q

What can cross between interstitial fluid and plasma?

A
  • Na+

- K+

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19
Q

What cannot cross between interstitial fluid and plasma?

A
  • Proteins
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20
Q

What is an ultra-filtrate of plasma?

A

Interstitial fluid

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21
Q

Permeability of solutes (least to most)

A
  • Ions
  • Large uncharged polar molecules
  • Small uncharged polar molecules
  • Hydrophobic molecules
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22
Q

Examples of Ions

A
  • H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+

- Requires channels

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23
Q

Examples of uncharged polar molecules

A

Glucose, sucrose

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24
Q

Examples of Small uncharged polar molecules

A

H2O, urea, glycerol

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25
Q

Examples of hydrophobic molecules

A

O2, CO2, N2, steroid hormones

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26
Q

Downhill transport

A
  • Substances moving down a concentration gradient, from high to low concentration
  • Passive transport
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27
Q

Types of passive transport

A
  • Simple diffusion

- Facilitated diffusion

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28
Q

Energy requirements of passive transport

A

No energy required

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29
Q

Uphill transport

A
  • Substances moving against a concentration gradient, from low to high concentration
  • Active transport
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30
Q

Types of active transport

A
  • Primary active transport

- Secondary active transport

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31
Q

Energy requirements of passive transport

A

Requires ATP, either directly or indirectly

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32
Q

Main classes of membrane transport proteins

A
  • Channels

- Transporters

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33
Q

Are channels for active or passive transport?

A
  • ALWAYS passive

- Much faster

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34
Q

Are transporters for active or passive transport?

A

Can be passive or active

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35
Q

Which kinds of transport require a channel protein?

A
  • Facilitated diffusion

- All forms of active transport

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36
Q

When might a channel be used for simple diffusion?

A
  • Ions cannot pass through the membrane without a channel protein
  • Important characteristic is following the laws of simple diffusion
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37
Q

What is the driving force for diffusion?

A

Random molecular movement down the concentration gradient

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38
Q

Determinants of simple diffusion

A
  • Amount of substance available (concentration)
  • Velocity of motion (like if it’s hotter)
  • Number and size of openings (permeability)
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39
Q

Flow

A
  • AKA flux

- Movement of fluids from one point to another

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40
Q

What causes flow?

A

Any form of gradient, almost always a combination of flows

  • Chemical
  • Electric
  • Pressure
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41
Q

Other important characteristics of flow

A
  • Always some form of resistance/opposition

- Resistance can be varied or physiologically controlled

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42
Q

Do molecules diffuse independently of each other?

A

Yes

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43
Q

Why does flow not always occur where there is a gradient?

A

If permeability is at 0, then it doesn’t matter how big the gradient is, flow will not occur

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44
Q

Units of measurement

A
  • Mole –> molarity
  • Equivalent
  • Osmole
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45
Q

Mole

A

6 x 10^23 of a substance

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46
Q

Molarity

A

Mole/Liter

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47
Q

Equivalent

A
  • Describes the amount of charged (ionized) solute

- Moles x Valence

48
Q

Osmole

A
  • Number of particles that dissolve into solution

- NaCl vs CaCl2

49
Q

Pores

A
  • Integral membrane protein

- ALWAYS open

50
Q

What factors determine the sensitivity of a pore?

A
  • Diameter

- Electrical charge

51
Q

Channels

A
  • Similar to pores

- Controlled by gates

52
Q

Types of gated channels

A
  • Voltage gated
  • Ligand gated
  • Mechanically gated
53
Q

Voltage-Gated Channels

A

Gate will open based on a change in potential

54
Q

Ligand-Gated Channels

A

Gate will open when the right molecule binds to a receptor

55
Q

Mechanically-Gated Channels

A

Change in pressure opens the channel

56
Q

How many gates does the voltage-gated Na+ channel have?

A
  • 2
  • Activation gate
  • Inactivation gate
57
Q

What limits the maximum rate of facilitated diffusion?

A
  • Saturation

- Rate of conformational change/transport

58
Q

Saturation

A

Limited number of carrier proteins and binding sites

59
Q

Rate of conformational change/transport

A

Rate of transport cannot exceed the rate of conformational change

60
Q

Factors that affect net diffusion

A
  • Concentration gradient
  • Partition coefficient (K)
  • Diffusion coefficient (D)
  • Thickness of the membrane
  • Surface area (A)
61
Q

Concentration gradient

A
  • Difference in concentration across the membrane

- C(a) - C(b)

62
Q

Partition coefficient (K)

A

Describes the solubility of the solute in oil vs water

63
Q

Diffusion coefficient (D)

A

Depends on:

  • Size of molecule
  • Viscosity of the medium
64
Q

Thickness of the membrane

A

Longer distance to cover = slower diffusion rate

65
Q

Surface area (A)

A

Greater surface area available = greater diffusion rate

66
Q

Additional factors affecting net diffusion if the solute is an electrolyte

A
  • Potential difference across the membrane

- Diffusion potential

67
Q

Nernst potential

A
  • Equilibrium potential

- Theoretical potential at which the electric gradient is equal and opposite to the concentration gradient

68
Q

Primary Active Transport

A

Energy is directly taken from ATP hydrolysis

69
Q

Secondary Active Transport

A

Energy is taken indirectly from ATP hydrolysis, usually the electrochemical gradient created by primary active transport

70
Q

Uniport

A

Move a single molecule using the carrier protein

71
Q

Symport

A

Moving two different molecules in the same direction using the carrier protein

72
Q

Antiport

A

Moving two different molecules in opposite directions using the carrier protein

73
Q

The Na+/K+ pump maintains which ion concentrations?

A
  • Na+ outside the cell

- K+ inside the cell

74
Q

Electrogenic

A

Contributes to the negative resting membrane potential

75
Q

How much does the Na+/K+ pump contribute to the membrane potential?

A

~10%

76
Q

How much energy is required to power the Na+/K+ pump?

A

60-70% of energy requirements in nerve cells

77
Q

In addition to maintaining ionic concentrations, what does the Na+/K+ pump do?

A

It is important for controlling cell volume

78
Q

Class of drugs that inhibit the Na+/K+ ATPase

A

Cardiac glycosides

79
Q

Examples of cardiac glycosides

A
  • Oubain

- Digitalis

80
Q

SGLT

A

Sodium Glucose Linked Transporter

81
Q

How is the SGLT an example of secondary active transport?

A

It gets its energy from the concentration gradient of Na+ created by the Na+/K+ ATPase to drive cotransport of Na+ and glucose

82
Q

Cooperative binding in the SGLT

A

The binding of Na+ to the transporter increases its affinity for glucose, and it will only work if both solutes are bound to the protein

83
Q

Osmosis

A

Flow of water across a semipermeable membrane due to a difference in solute concentration

84
Q

Why does osmosis occur?

A

Due to a pressure difference

85
Q

Osmotic Pressure

A

For 1 mOsm concentration gradient of IMPERMEABLE solute, 19.3 mmHg of osmotic pressure is exerted across the cell membrane

86
Q

What determines osmotic pressure?

A

The number of particles/unit volume (not mass)

87
Q

Osmolarity

A
  • Concentration of osmotically active particles (mOsm/L)

- Osmolarity = gC

88
Q

g

A

Number of particles/mole in solution (Osm/mol)

89
Q

C

A

Concentration (mmol/L)

90
Q

Osmolality

A

Concentration of osmotically active particles/kg of solvent

91
Q

Tonicity

A
  • Effect of the solution on the volume of the cell

- Takes into account the ability of the molecules to cross the membrane

92
Q

Isotonic

A
  • Osmolarity of solution = osmolarity of ICF

- No change in cell volume

93
Q

Hypertonic

A
  • Osmolarity of solution > osmolarity of ICF

- Cell shrinks

94
Q

Hypotonic

A
  • Osmolarity of solution < osmolarity of ICF

- Cell swells

95
Q

Which ion concentration is an indicator of plasma osmolarity?

A
  • [Na+]

- Accounts for ~90% of ECF

96
Q

Normal range for [Na+]

A

135-145 mEq/L

97
Q

Hyponatremia

A
  • [Na+] < 135 mEq/L

- Loss of NaCl –> hyponatremia and dehydration

98
Q

Possible causes of hyponatremia

A
  • Diarrhea
  • Vomiting
  • Diuretic overuse (inhibits kidneys from retaining Na+)
  • SIADH (increased water retention) –> dilutes Na+ and causes hypoosmolarity
99
Q

Consequences of hyponatremia

A
  • Brain cell edema

- Increased intracranial pressure and neurological symptoms

100
Q

Neurological symptoms of brain cell edema

A
  • Headache
  • Nausea
  • Lethargy
  • Disorientation
  • Seizures
  • Coma
  • Herniation
101
Q

What are possible effects of lowered Na+ concentration in the brain?

A
  • Altered nerve and muscle action potentials

- May cause twitching, depressed reflexes, and weakness

102
Q

How is brain cell edema treated?

A

Mannitol doesn’t cross the BBB and creates the osmotic gradient needed to pull water out of brain tissue

103
Q

Does application of mannitol need to happen quickly or slowly?

A

Slowly

104
Q

Why does application of mannitol need to happen slowly?

A

To prevent osmotic demyelination syndrome

105
Q

Osmotic demyelination syndrome

A

If water balance is restored too quickly, the glial cells will shrink and die

106
Q

What is the effect of glial cells shrinking and dying?

A
  • Glial cells synthesize myelin

- If these cells die, myelination of nerves in CNS will stop (usually pons affected)

107
Q

What can be done to reverse osmotic demyelination syndrome?

A

Effects are often irreversible

108
Q

How common is hyponatremia?

A
  • Most common electrolyte disorder in clinical practice

- 15-25% of hospitalized patients

109
Q

What special population is at greater risk for hyponatremia?

A
  • Elderly

- Contributes to cognitive deficits, falls, fractures, and long-term hospitalizations

110
Q

Hypernatremia

A

[Na+] > 145 mEq/L

111
Q

When will severe symptoms occur due to hypernatremia?

A

[Na+] > 160 mEq/L

112
Q

What can cause hypernatremia?

A

Due to loss of water from ECF or excess Na+

113
Q

Is hypo- or hypernatremia more common?

A

Hyponatremia

114
Q

Clinical manifestations of hypernatremia

A
  • Dehydration
  • Thirst
  • Weight gain
  • Bounding pulse
  • Increased BP
115
Q

Neurological manifestations of hypernatremia

A
  • Due to shrinking of cells and altered action potentials
  • Twitching
  • Hyperreflexia
  • Convulsions
  • Cerebral hemorrhage
116
Q

How is hypernatremia corrected?

A
  • Via hypo-osmotic solutions

- Slow correction is essential

South College Human Physiology (4 decks)

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