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)
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
3
Q
What percentage of proteins in an animal cell’s genome are membrane proteins?
A
30%
4
Q
Most common type of phospholipid
A
Phosphoglycerides
5
Q
Structure of a phospholipid
A
- Glycerol back bone w/ attached phosphate group
- 2 hydrocarbon tails
6
Q
What kind of bond does one of the hydrocarbon tails have?
A
cis-double bond (creates a bend)
7
Q
What is the effect of the cis-double bond in the hydrocarbon tail?
A
- Thinner membrane
- More fluidity (space between phospholipid)
8
Q
How to phospholipid bilayers formed?
A
Spontaneously
9
Q
Amphiphilic
A
One side of the bilayer is hydrophilic, the other is hydrophobic
10
Q
What advantage does spontaneously forming the bilayer provide?
A
Provides important self-healing capability
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
12
Q
Why is restricting proteins to specific domains important?
A
Prevent flow of solutes in the wrong direction
13
Q
What percentage of body weight is total body water (TBW)
A
- 50-70%
- Inversely proportional to body fat
14
Q
What are the divisions of total body water (TBW)?
A
- Intracellular fluid (ICF)
- Extracellular fluid (ECF)
15
Q
How much of TBW is intracellular fluid (ICF)?
A
ICF = 2/3 TBW
16
Q
How much of TBW is extracellular fluid?
A
ECF = 1/3 TBS
17
Q
Extracellular fluid is made of what?
A
- Interstitial fluid
- Plasma
18
Q
What can cross between interstitial fluid and plasma?
A
- Na+
- K+
19
Q
What cannot cross between interstitial fluid and plasma?
A
- Proteins
20
Q
What is an ultra-filtrate of plasma?
A
Interstitial fluid
21
Q
Permeability of solutes (least to most)
A
- Ions
- Large uncharged polar molecules
- Small uncharged polar molecules
- Hydrophobic molecules
22
Q
Examples of Ions
A
- H+, Na+, HCO3-, K+, Ca2+, Cl-, Mg2+
- Requires channels
23
Q
Examples of uncharged polar molecules
A
Glucose, sucrose
24
Q
Examples of Small uncharged polar molecules
A
H2O, urea, glycerol
25
Examples of hydrophobic molecules
O2, CO2, N2, steroid hormones
26
Downhill transport
- Substances moving down a concentration gradient, from high to low concentration
- Passive transport
27
Types of passive transport
- Simple diffusion
| - Facilitated diffusion
28
Energy requirements of passive transport
No energy required
29
Uphill transport
- Substances moving against a concentration gradient, from low to high concentration
- Active transport
30
Types of active transport
- Primary active transport
| - Secondary active transport
31
Energy requirements of passive transport
Requires ATP, either directly or indirectly
32
Main classes of membrane transport proteins
- Channels
| - Transporters
33
Are channels for active or passive transport?
- ALWAYS passive
| - Much faster
34
Are transporters for active or passive transport?
Can be passive or active
35
Which kinds of transport require a channel protein?
- Facilitated diffusion
| - All forms of active transport
36
When might a channel be used for simple diffusion?
- Ions cannot pass through the membrane without a channel protein
- Important characteristic is following the laws of simple diffusion
37
What is the driving force for diffusion?
Random molecular movement down the concentration gradient
38
Determinants of simple diffusion
- Amount of substance available (concentration)
- Velocity of motion (like if it's hotter)
- Number and size of openings (permeability)
39
Flow
- AKA flux
| - Movement of fluids from one point to another
40
What causes flow?
Any form of gradient, almost always a combination of flows
- Chemical
- Electric
- Pressure
41
Other important characteristics of flow
- Always some form of resistance/opposition
| - Resistance can be varied or physiologically controlled
42
Do molecules diffuse independently of each other?
Yes
43
Why does flow not always occur where there is a gradient?
If permeability is at 0, then it doesn't matter how big the gradient is, flow will not occur
44
Units of measurement
- Mole --> molarity
- Equivalent
- Osmole
45
Mole
6 x 10^23 of a substance
46
Molarity
Mole/Liter
47
Equivalent
- Describes the amount of charged (ionized) solute
| - Moles x Valence
48
Osmole
- Number of particles that dissolve into solution
| - NaCl vs CaCl2
49
Pores
- Integral membrane protein
| - ALWAYS open
50
What factors determine the sensitivity of a pore?
- Diameter
| - Electrical charge
51
Channels
- Similar to pores
| - Controlled by gates
52
Types of gated channels
- Voltage gated
- Ligand gated
- Mechanically gated
53
Voltage-Gated Channels
Gate will open based on a change in potential
54
Ligand-Gated Channels
Gate will open when the right molecule binds to a receptor
55
Mechanically-Gated Channels
Change in pressure opens the channel
56
How many gates does the voltage-gated Na+ channel have?
- 2
- Activation gate
- Inactivation gate
57
What limits the maximum rate of facilitated diffusion?
- Saturation
| - Rate of conformational change/transport
58
Saturation
Limited number of carrier proteins and binding sites
59
Rate of conformational change/transport
Rate of transport cannot exceed the rate of conformational change
60
Factors that affect net diffusion
- Concentration gradient
- Partition coefficient (K)
- Diffusion coefficient (D)
- Thickness of the membrane
- Surface area (A)
61
Concentration gradient
- Difference in concentration across the membrane
| - C(a) - C(b)
62
Partition coefficient (K)
Describes the solubility of the solute in oil vs water
63
Diffusion coefficient (D)
Depends on:
- Size of molecule
- Viscosity of the medium
64
Thickness of the membrane
Longer distance to cover = slower diffusion rate
65
Surface area (A)
Greater surface area available = greater diffusion rate
66
Additional factors affecting net diffusion if the solute is an electrolyte
- Potential difference across the membrane
| - Diffusion potential
67
Nernst potential
- Equilibrium potential
| - Theoretical potential at which the electric gradient is equal and opposite to the concentration gradient
68
Primary Active Transport
Energy is directly taken from ATP hydrolysis
69
Secondary Active Transport
Energy is taken indirectly from ATP hydrolysis, usually the electrochemical gradient created by primary active transport
70
Uniport
Move a single molecule using the carrier protein
71
Symport
Moving two different molecules in the same direction using the carrier protein
72
Antiport
Moving two different molecules in opposite directions using the carrier protein
73
The Na+/K+ pump maintains which ion concentrations?
- Na+ outside the cell
| - K+ inside the cell
74
Electrogenic
Contributes to the negative resting membrane potential
75
How much does the Na+/K+ pump contribute to the membrane potential?
~10%
76
How much energy is required to power the Na+/K+ pump?
60-70% of energy requirements in nerve cells
77
In addition to maintaining ionic concentrations, what does the Na+/K+ pump do?
It is important for controlling cell volume
78
Class of drugs that inhibit the Na+/K+ ATPase
Cardiac glycosides
79
Examples of cardiac glycosides
- Oubain
| - Digitalis
80
SGLT
Sodium Glucose Linked Transporter
81
How is the SGLT an example of secondary active transport?
It gets its energy from the concentration gradient of Na+ created by the Na+/K+ ATPase to drive cotransport of Na+ and glucose
82
Cooperative binding in the SGLT
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
Osmosis
Flow of water across a semipermeable membrane due to a difference in solute concentration
84
Why does osmosis occur?
Due to a pressure difference
85
Osmotic Pressure
For 1 mOsm concentration gradient of IMPERMEABLE solute, 19.3 mmHg of osmotic pressure is exerted across the cell membrane
86
What determines osmotic pressure?
The number of particles/unit volume (not mass)
87
Osmolarity
- Concentration of osmotically active particles (mOsm/L)
| - Osmolarity = gC
88
g
Number of particles/mole in solution (Osm/mol)
89
C
Concentration (mmol/L)
90
Osmolality
Concentration of osmotically active particles/kg of solvent
91
Tonicity
- Effect of the solution on the volume of the cell
| - Takes into account the ability of the molecules to cross the membrane
92
Isotonic
- Osmolarity of solution = osmolarity of ICF
| - No change in cell volume
93
Hypertonic
- Osmolarity of solution > osmolarity of ICF
| - Cell shrinks
94
Hypotonic
- Osmolarity of solution < osmolarity of ICF
| - Cell swells
95
Which ion concentration is an indicator of plasma osmolarity?
- [Na+]
| - Accounts for ~90% of ECF
96
Normal range for [Na+]
135-145 mEq/L
97
Hyponatremia
- [Na+] < 135 mEq/L
| - Loss of NaCl --> hyponatremia and dehydration
98
Possible causes of hyponatremia
- Diarrhea
- Vomiting
- Diuretic overuse (inhibits kidneys from retaining Na+)
- SIADH (increased water retention) --> dilutes Na+ and causes hypoosmolarity
99
Consequences of hyponatremia
- Brain cell edema
| - Increased intracranial pressure and neurological symptoms
100
Neurological symptoms of brain cell edema
- Headache
- Nausea
- Lethargy
- Disorientation
- Seizures
- Coma
- Herniation
101
What are possible effects of lowered Na+ concentration in the brain?
- Altered nerve and muscle action potentials
| - May cause twitching, depressed reflexes, and weakness
102
How is brain cell edema treated?
Mannitol doesn't cross the BBB and creates the osmotic gradient needed to pull water out of brain tissue
103
Does application of mannitol need to happen quickly or slowly?
Slowly
104
Why does application of mannitol need to happen slowly?
To prevent osmotic demyelination syndrome
105
Osmotic demyelination syndrome
If water balance is restored too quickly, the glial cells will shrink and die
106
What is the effect of glial cells shrinking and dying?
- Glial cells synthesize myelin
| - If these cells die, myelination of nerves in CNS will stop (usually pons affected)
107
What can be done to reverse osmotic demyelination syndrome?
Effects are often irreversible
108
How common is hyponatremia?
- Most common electrolyte disorder in clinical practice
| - 15-25% of hospitalized patients
109
What special population is at greater risk for hyponatremia?
- Elderly
| - Contributes to cognitive deficits, falls, fractures, and long-term hospitalizations
110
Hypernatremia
[Na+] > 145 mEq/L
111
When will severe symptoms occur due to hypernatremia?
[Na+] > 160 mEq/L
112
What can cause hypernatremia?
Due to loss of water from ECF or excess Na+
113
Is hypo- or hypernatremia more common?
Hyponatremia
114
Clinical manifestations of hypernatremia
- Dehydration
- Thirst
- Weight gain
- Bounding pulse
- Increased BP
115
Neurological manifestations of hypernatremia
- Due to shrinking of cells and altered action potentials
- Twitching
- Hyperreflexia
- Convulsions
- Cerebral hemorrhage
116
How is hypernatremia corrected?
- Via hypo-osmotic solutions
| - Slow correction is essential
