Basic Cellular Physiology Flashcards
Fluid distribution in the body
Intracellular - 27 liters, 2/3 of total
Extracellular - 13 liters, + 5 liters “third space,” 1/3 of total
Fluid distribution in the body
Intracellular - 27 liters, 2/3 of total
Extracellular - 13 liters, + 5 liters “third space,” 1/3 of total
Nernst Equation
E = (60/Z) x log10 (Co/Ci)
Where E = equilibrium potential,
Z = charge valence of the ion, and
C = concentration
Osmolarity
Describes the total concentration of solute particles in a solution
Ex: a 1M solution of CaCl2 gives a 3osM solution
Tonicity
Describes the effect of a solution on cell volume.
Any solution that makes a cell shrink is hypertonic; any solution that makes a cell swell is hypotonic.
Ionic Driving Force
DF = Vm - Eion
Iion = (Vm-Eion) * Gion
Where I is flow and G is conductance
Therefore, movement of an ion across the membrane depends on the ionic driving force as well as membrane conductivity to that ion
Donnan Rule
[K]o[Cl]o = [K]i[Cl]i
Na/K Pump - Mechanism
Pumps 3 Na+ out of the cell for every 2 K+ brought into the cell at a maximum rate of 100 cycles per second.
While ATP-bound, the pump has higher affinity for Na+ and so binds 3 intracellular Na+ ions; ATP hydrolysis phosphorylates the pump, triggering a conformational change that closes the inner gate and opens the outer gate; the phosphorylated pump has higher K+ affinity so 2 Na+ molecules are released extracellularly and 2 K+ molecules are bound from the ECF; dephosphorylation of the pump triggers closing of the outer gate and opening of the inner gate; 2K+ are released intracellularly, and ATP binds again.
Hyperkalemia
Acute increase in extracellular potassium concentration, often caused by potassium release from cells following crush injury, burn, etc. May cause depolarization of cardiac cells, resulting in cardiac arrhythmia
Treatment: CBIGK
C- Calcium - shields negative charges on cell membrane, hyper-polarizing the cell
B - Bicarbonate (HCO3-) drives the K+/H+ toward K+ re-uptake
I - Insulin
G - Glucose - with insulin, works to increase the activity of the Na/K pump (K reuptake)
K - Kaexolate - an inert anion bound to Na+ delivered into the lumen of the GI tract; ion exchange resin preferentially binds K+ over Na+, facilitating its excretion
Nernst Equation
E = (60/Z) x log10 (Co/Ci)
Where E = equilibrium potential, Z = charge valence of the ion, and C = concentration
Osmolarity
Describes the total concentration of solute particles in a solution
Ex: a 1M solution of CaCl2 gives a 3osM solution
Tonicity
Describes the effect of a solution on cell volume.
Any solution that makes a cell shrink is hypertonic; any solution that makes a cell swell is hypotonic.
Ionic Driving Force
DF = Vm - Eion
Iion = (Vm-Eion) * Gion
Where I is flow and G is conductance
Therefore, movement of an ion across the membrane depends on the ionic driving force as well as membrane conductivity to that ion
Donnan Rule
[K]o[Cl]o = [K]i[Cl]i
Na/K Pump
Pumps 3 Na+ out of the cell for every 2 K+ brought into the cell at a maximum rate of 100 cycles per second. ATP binds the pump, signaling the opening of the inner gate which releases 2 K and takes up 3 Na. ATP hydrolysis closes the inner gate and opens the outer gate, releasing 2 Na and taking up 2 K.
Hyperkalemia
Acute increase in extracellular potassium concentration, often caused by potassium release from cells following crush injury, burn, etc. May cause depolarization of cardiac cells, resulting in cardiac arrhythmia
Treatment: CBIGK
C- Calcium
B - Bicarbonate (HCO3-) drives the K+/H+ toward K+ re-uptake
I - Insulin
G - Glucose - with insulin, works to increase the activity of the Na/K pump (K reuptake)
K - Kaexolate - an inert anion bound to Na+ delivered into the lumen of the GI tract; ion exchange resin preferentially binds K+ over Na+, facilitating its excretion
Law of Mass Action
For any reaction A + B in equilibrium with C + D,
Vf = kf * [A][B] and
Vr = kr * [C][D]
Keq = kf/kr = [C][D]/[A][B]
Blood pH, venous vs. arterial
Arterial = 7.34 - 7.44 Venous = 7.28 - 7.42
Venous blood is more acidic because it carries more CO2 in equilibrium with carbonic acid
pH-dependent activity of Pepsin and Trypsin
Pepsin (a stomach protease) is maximally active ~ pH 2
Trypsin (a duodenal protease) is maximally active ~ pH 7
Henderson Hasselbach Equation
pH = pKa + log ([base]/[acid])
When pH = pKa, an acid/base is 50% deprotonated and 50% protonated
Within 1 pH unit of pK, the acid/base will exist 90% in its favored state and 10% in its unfavored state
Within 2 pH units of pK, the acid/base will exist 99% in its favored state and 1% in its unfavored state
Clinical presentations related to acid/base chemistry
Normal bicarbonate = 24 mM
Normal pCO2 = 40 mmHg
Normal CO2 concentration = 1.2mM
Changes in [HCO3-] away from it’s normal value cause metabolic acidosis/alkylosis
Changes in pCO2 away from it’s normal value cause respiratory acidosis/alkylosis
Modified H-H equation for the bicarbonate system
pH = 6.1 + log [HCO3-] / .03PCO2
What molecular phenomena are responsible for the refractory period of an AP?
The absolute refractory period is caused by closing of the NaV inactivation (h) gate; although the activation (m) gate may be open in response to depolarization, no Na+ current will flow
The relative refractory period is caused by K+ channels that remain open; it will take a larger depolarizing stimulus to reach threshold if outward K+ conductance is still high
NaV Safety Factor
Axons contain 5-10x the minimum number of NaV channels required to fire an AP; this phenomenon ensures that APs can propagate down multiple axonal branches, increases the frequency at which cells can fire APs by shortening the absolute refractory time, and increases the velocity of AP propagation
