What percentage of our body weight is water?
What is TBW and what is it composed of?
Total body water = ECF (extracellular fluid) + ICF (intracellular fluid)
What is are the amounts of ECF and ICF in the body?
1/3 of TBW = ECF 2/3 = ICF
What are the types of extracellular fluid?
Plasma volume (PV) and interstitial fluid
What percentage of our ECF is plasma volume? What percentage is interstitial fluid?
20% Plasma volume 80% interstitial fluid
What is our blood volume?
Plasma volume + volume of blood cells (hematocrit)
What is a normal hematocrit?
What is transcellular fluid?
A small part of ECF inside organs (e.g. cerebrospinal fluid) It is ignored in calculations
What is the standard osmolality of body fluids?
What types of fluid/body compartments are similar? Different?
Interstitial fluid and plasma are nearly identical (highly permeable endothelium) while intracellular fluid is markedly different (due to PM)
What are the primary (highest concentration) ions in the intracellular fluid?
K+ (highest), phosphates, and some Mg++ and proteins
What are the primary (highest concentration) ions in the extracellular fluid?
Na+ (highest), Cl- with some bicarb
Is the net charge neutral in the ICF? in the ECF?
Neutral in both
How is solute flux defined?
The number of molecules (or moles) crossing the unit area in the unit time
What is the equation for flux of a neutral solute at concentrations C1 and C2?
J = P(C1 - C2) = P x (delta)C P = permeability J = flux
What is macroscopic electroneutrality?
The idea that the charge transfer required for creating the electrical potential difference across cell membranes is several orders of magnitude smaller than the typical ion concentrations of a cell. Thus no difference between the the number of + or - mEq/L can be found at either side of the cell membrane using standard chemical measurements.
What is the equation for membrane permeability?
P = D x Beta / deltaX D is the diffusion coeffcient Beta is the partition coefficient deltaX is the thickness of the membrane
Diffusion coefficients are _______ proportional to molecular weight.
____ molecular weight and _____ hydrophobicity have a relatively high permeability across
Low MW (large D) and High hydrophobicity (large Beta)
What is the equation for work done by chemical potential?
MuI = RTln Ci + constant Ci is concentration of the substance, i
What is the equation for work done by chemical and electric potential (e.g for an ion)?
The change in MuI (electrochemical potential) is analogous to what?
Change in Gibbs free energy (i.e. negative MuI is passive movement).
What does the Nernst equation tell you?
The value of the membrane potential when the ion is at equilibrium (i.e. equilibrium potential)
What is the equation for the Nernst equation?
Simplified: Ei = (61/Zi) log [Cout/Cin]
What term is the net driving force?
Vm - Ei (Vm = membrane potential, Ei = equilibrium potential for the ion) Note, when these two values equal one another, the net driving force is zero!
Flow = ?
Conductance x Force
What equation can be used to measure conductance (permeability related to ion net driving force)?
Electric current carried by a permeable ion across membrane is _____ related to the ion net driving force.
What equation can be used to understand ionic equilibria in systems with more than one ion (e.g. Na and Cl)?
What is the Gibbs-Donna equilibrium?
Equilibrium disitribution of permeant ions in the presence of non-permeant proteins.
What are the 3 factors that determine Gibbs-Donnan equilibrium?
1. The concentration of cations in equivalents/L (Eq/L) must equal that of the anions on each side of the PM. 2. Concentration of permeat cations must be > and the concentration of permeant anions must be
What is the most important physiological effect that results from the Gibbs-Donnan Equilibrium?
The negatively charged plasma proteins cause a slight deficit of anions and excess of cations in plasma water compared to the interstitial fluid (about 5%).
What is the second most important physiological effect from Gibbs-Donnan Equilibrium?
The extra osmoles from the permeat ions plus the impermeant proteins in the plasma cause a higher oncotic pressure in the plasma.
Net flux is proportional to what?
What does the partition coefficient represent?
The solubility of the molecule in each side of the diffusion barrier (e.g. lipid or water)
Do ions have low or high permeability in lipid membranes?
What is the voltage of the inside of the cell?