Shared Flashcard Set


"Membrane Transport"
9/10/07--for quiz 1
Not Applicable

Additional Physiology Flashcards




What is volume and composition of body fluids?
Total Body Water (TBW)
50-70% body weight

I) Intracellular fluid (ICF) ~2/3rds TBW
-25 L

II) Extracellular fluid~1/3rd TBW

a) Interstitial Fluid-13 L

b) Plasma-3 L

III) Transcellular--1L
What is difference b/w moles, osmoles, equivalents, and pX+?
1) Mole: 6 X 1023 molecules of a substance

2) Equivalent: amount of charged (ionized) solute and is the # of moles of solute multiplied by its valence.

Example: 1 mole of CaCl2 dissociates into two equivalents of calcium and two equivalents of chloride. (Ca = 2+ , Cl = 1-)

3) Osmole: number of particles into which a solute dissociates
Example: 1 mmol/L of CaCl2 dissociates into 3 mOsm/L.
(1 Ca particle, 2 Cl particles)
What is Fick's Law of Diffusion?

J = Net rate of diffusion
D = Diffusion coefficient
A = Area of the plane diffusing across
dc/dx = Concentration gradient
What is Einstein relation for calculating diffusion times?
Δx = change in diffusion distance
Dt = change in time
What is the main idea behind Stokes-Einstein relation?
D= kT/ 6πrη

D = Diffusion coefficient
K = Boltzmann’s constant
T = absolute temperature (in Kelvins)
R = molecular radius
η = viscosity of medium
How can various factors influence diffusion coefficient in the Stokes-Einstein relation?
Parameters that influence diffusion coefficient:

1) Viscosity of medium (intrinsic property)

--syrup (higher viscosity, slower diffusion)
--water (lower viscosity, more rapid diffusion)

2)Temperature- ↑ Temp = ↑ diffusion

3) Radius of molecule: ↑ radius = ↓ diffusion
What is osmosis and osmotic pressure?
Osmosis: flow of water across a semipermeable membrane due to a difference in solute concentration.

Osmotic pressure: pressure required to prevent the flow of water
What is Van't Hoff's Law? How can it be used to calculate osmotic pressure?
Van’t Hoff’s Law: ∏= g C σ RT

Π = osmotic pressure (atm)
g = particles per mole in solution (Osm/L)
C = concentration (mmol/L)
σ = reflection coefficient (0 to 1; 1 being impermeable, 0 is permeable)
R = gas constant
T = absolute temperature
What is difference between permeant and impermeant solutes?

How can this lead to different definitions of osmolarity and tonicity?
Permeant solute: moves freely across semipermeable membrane

Impermeant solute: do not passively diffuse into or out of semipermeable membrane, usually creates hypertonic soln.

osmolarity--(don't memorize this, but is= gC, where g=number of particles in solution and C=concentration of particles--it is important whether molecule DISSOCIATES in solution) measures number of dissolved particles in water.
isoosmotic--same number of dissolved particles

tonicity--measures tendancy of solution to resist expansion of intracellular volume
isotonic--no water movement.

How do permeant v. impermeant solutes influence osmolarity and tonicity?
Osmolarity: measures effective gradient for water assuming all the solute is completely impermeant (measured per L). Ex: 300 millimolar solution of glucose (1 osmole), a 300 millimolar solution of urea (1 osmole), and a 150 millimolar solution of NaCl (2 osmoles) each have the same osmolarity.

Tonicity: describes the tendency of a solution to resist expansion of the intracellular volume. Sometimes referred to as “effective” osmolarity.

Operational Definition
Two solutions are isosmotic when they have the same number of dissolved particles, regardless of how much water would flow across a given membrane barrier. In
contrast, two solutions are isotonic when they would cause no water movement across a membrane barrier, regardless of how many particles are dissolved.

In the example given above, a 150 mM NaCl solution would be isosmotic to the inside of a cell, and it would also be isotonic--the cell would not swell or shrink when placed in this solution (cell is normally ~300 mM). On the other hand, a 300 mM urea solution, while still isosmotic would cause the cell to swell and burst (due to its permeability). This isosmotic urea solution is not isotonic. Instead it has a lower tonicity (hypotonic).

If different osmotic pressures, then not isotonic. If different reflection coefficients (σ) or “permeability”, not isotonic.
What is Gibbs-Donnan equilibrium?
Definition: Plasma contains impermeable negative charges that leads to a redistribution of permeant anions (Cl-) and cations (Na+)

[Na+]o/[Na+]i= [Cl -]i/[Cl -]o

-->Na is higher outside cell, Cl is higher inside cell--so [Na]o/[Na]i=[Ca]i/[Ca]o
What is anion gap? How is it calculated?
Anion Gapplasma = [Na+]plasma - ([Cl-]plasma + [HCO3-]plasma)

Useful for diagnosis of acid-base disorders. The anion gap is based upon the principle of electroneutrality: for any body fluid compartment (ie plasma), the concentrations of cations and anions must equal.
What is facilitated diffusion?

What is good example of facilitated diffusion?
-->A process whereby a substance passes through the membrane
with the aid of an integral membrane protein

--Substances move down their electrochemical gradient

--Saturation, stereospecificity, competition are all relevant

--Does not require energy (ATP)

--Ex: ion channels, transporter (GLUT 4 for D-glucose
What is primary active transport?

What is a good example of this?
-->Movement of a substance uphill (against conc gradient); the energy source is directly coupled to the transport process.

--Requires ATP

--Ex: Na-K pump, Ca ATPase
What is secondary active transport?

What is a good example of this?
-->transport of two or more solutes is coupled

--One molecule moves down conc gradient, provides energy for uphill movement of other molecule

--ATP supplied “indirectly” via primary molecule

--If uphill molecule moves in same direction as Na+ = cotransport or symport
-Ex: Na-glucose cotransport

--If uphill molecule moves in opposite direction as Na+ = countertransport
-Ex: Ca-Na exchange in muscle
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