Diffusion, Ionic Concentration, Electrochemical Potential, and Excitable Tissue Flashcards
movement of solute down its concentration gradient until concentrations are equal
simple diffusion
Na+, K+, Cl-, Ca++
important physiological ions
glucose, amino acids, lipids
important physiological nutrients
O2, CO2
important physiological gases
diffusion of water down its concentration gradient
water moves from more dilute to more concentrated solute solutions
osmosis
the force that would need to be applied on a compartment to prevent the migration of water into that apartment, due to unequal solute concentrations
osmotic pressure
a solution with high solute load would have a high osmotic pressure relative to a pure water solution
osmotic pressure ex.
1 mole of solute dissolved in 1 liter of water
(solute concentration)
molality
the total molality of a water solution
osmolality
1m glucose + 1 m fructose = 2 osmol/L
osmolality of non-ionic substances
1m NaCl yields 2 osmol/L
osmolality of ionic substances
describes the effect of net movement of water due to osmosis into or out of the cell
(what happens to cell volume when exposed to a solution)
tonicity
no net movement of water
isotonic solution
Blood plasma = 300 mOsm
0.3 m glucose = 300 mOsm (5g glusoce/100mL H2O)
0.15m NaCl = 300 mOsm (0.9g NaCl/100mL H2O)
standard solutions, (isotonic)
higher solute load than inside the cell, water will move from cell to solution, causing the cell the shrink (crenation)
hypertonic solution
lower solute load inside the cell, water will move into the cell from the solution causing the cell to expand and burst (Hemolysis)
hypotonic solution
(carrier mediated transport) involves a membrane carrier molecule
could become saturated (all carrier molecules are used)
facilitated diffusion
defines the distribution of ions in two aqueous compartments separated by membrane, where membrane is impermeable to at least one ionic species
Gibbs Donnan Equilibrium
determined by charge and concentration gradients
movement of ions
Gibbs Donnan Equilibrium equation
[K+]i[Cl-]i = [K+]o[Cl-]o
osmotic hydrostatic pressure calculation
P = 22.4 atm(delta[K+] + delta[Cl-] + delta[A-]
brain ischemia, low O2 shuts down Na+/K+ ATPase pump, ion balance is disturbed, water flows into cells, neurons swell and are damaged
Gibbs Donnan Equilibrium ex.
movement of an ion against its concentration gradient, requires ATP
Primary active transport
kinetic energy of a molecule moving downs its concentration gradient is coupled to move another molecule against its concentrating gradient (hitching a ride)
Secondary active transport
electrogenic (moves charge across a membrane)
located in the plasma membrane, ATP is the source, moves 3 Na+ out of the cell and 2 K+ in
establishes charge and concentration differences across the membrane
NA+/K+ ATPase pump
Na+/K+ ATPase pump steps
- 3 Na+ bind to transporter, ATP binds
- phosphate is cleaved, bind the pump
- confirmational change results, Na+ is released
- K+ now binds to outside of transporter
- Phosphate is released
- confirmation change results, K+ is released in the cell
a way to calculate equilibrium potential for individual ions
Nernst equation
Nernst equation
E = (61.5/Z) log([ion]out/[ion]in)
Z is ion valence
establishes equilibrium potential for cell, simultaneously using all ions
Goldmann Field equation
Goldmann Field Equation
61.5log((PK[ion]out + PNa[Ion]out + PCl[Ion]in)/(PK[ion]in + PNa[ion]in + PCl[Ion]out))
P = permeability coefficient
Permeability coefficients for a resting cell
PK = 1.0
PCl = 0.45
PNa = 0.04
Permeability coefficients for an excited state cell
PK = 1.0
PCl = 0.45
PNa = 20.0
ionic potential creates an electrical potential across the membrane
why nerve tissue is excitable
quantitative measure of irritability
the strength duration curve
the four important values derived from the strength duration curve
- Rheobase: minimum intensity in mV that still produces response
- Utilization time: the time necessary to produce Rheobase response
- Chronaxie: the duration in msec which a stimulus 2x Rheobase needs to produce a response
- Excitability: 1/Chronaxie
determinants of the charge and excitability of a cell (4)
- Phospholipid bilayer (permeable to water, impermeable to ions)
- Na+/K+ ATPase pump (ion inequality across the membrane)
- Nongated channels (channels that are always open to ions)
- Gated channels (channels that open or close depending on cell charge)
resting potential is established by
Nongated channels and the Na+/K+ ATPase pump
negative potential difference compared to extracellular fluid
-70 mV
passive channels, determine ion permeabilities, “leaky,” more permeable to K+ than Na+
Nongated channels
found in membrane, uses ATP, 3 Na+ out, 2K+ in, uses 60% of the cells energy
Na+/K+ ATPase pump
extracellular Na+ gate
M gate
intracellular Na+ gate
H gate
single extracellular gate
N gate
The time after an action potential when a neuron cannot be activated by another stimulus, controlled by Na+ gates
absolute refractory period
threshold for action potential is elevated because of hyperpolarization overshoot, requires strong stimulus
relative refractory period
pufferfish, tetrodotoxin, block Na+ channels, nerves cannot produce action potential, results in cardiac and respiratory failure
Fugu
inhibits the Na+/K+ ATPase pump
the role of Ouabain
