Fluid balance Flashcards
Extracellular fluid consists of…
Interstitial fluid
Blood plasma
Transcellular fluid
Interstitial fluid is formed by…
More fluid being pushed out in capillary beds than is being drawn back in
What are the main ions in ECF?
Na, Cl and HCO3-
What are the main ions in ICF?
K+, Mg, Protein
What is a mole?
an amount of substance that contains the number of molecules equal to Avogadro’s number (6 x 10 to the 23).
Define concentration
a measure of how much of a given solute is dissolved in a given volume of solvent : Usually moles per litre(dm3)
What is the difference between molarity and molality?
Molarity = number of moles per litre (use a M eg. 5M)
Molality = number of moles per kg of solvent (Use m eg. 5m)
One milliequivalent is equal to how many moles?
1 milieq = 10(-3) eq
so 1 meq = 1mmol
What is the water potential?
The tendency of the water molecules to move out of a solution is known as the water potential, Ψ.
How does water move with regard to water potentials?
Water always moves from a region of higher water potential to a region of lower water potential.
What is the water potential of pure water?
In pure water, the water potential is 0
What is the osmotic pressure?
This is the pressure, exerted by the solute particles in the solution, which prevents the movement of water across a membrane
Equivalent to the osmotic potential or Ψs
What are colloids?
Colloids are large molecular weight particles present in solution
What is oncotic pressure?
Oncotic pressure is the proportion of the total osmotic pressure in plasma exerted by colloids
What is the effect of hypertonic solution on cells?
Cells shrivel up and are plasmolyzed
What is the effect of hypotonic solution on cells?
Cells swell as they take on water and can lyse
What is an osmole?
Osmole = The number of ions or particles into which a solute dissociates in solution.
eg 1 mole of NaCl –> Na and Cl so is 2 osmoles
What is the difference between osmolality and osmolarity?
Osmolality is the number of osmoles of solute per kg solvent (temp independent)
Osmolarity is the number of osmoles per litre of solution
What is tonicity?
Tonicity is the effective osmolality and is equal to the sum of the concentration of the solutes which have the capacity to exert an osmotic force across the membrane.
What is the osmolality of serum and ECF in dogs?
300mOsm/kg
In hypotonic fluid loss what happens to ECF?
As the ECF is hypertonic the ECF Increases preserving circulating fluid volume
What is the effect of IV Isotonic crystalline fluid?
Plasma volume: Expanded proportionally to its volume of the ECF
ISF: Expanded
ICV: unchanged
What is the effect of IV Hypertonic crystalline fluid?
ISF increases so PV increases but ICV decreases
What is the effect of IV colloid fluid?
PV increases
ISF remains unchanged
ICV remains unchanged
What effect does slow change to ECF tonicity have on ICF?
No effect as Extracellular hypertonicity increases expression of genes encoding proteins that increase intracellular osmoles
