Fick's Principle in Volume Compartment Dynamics

Study Notes

Volume of compartment equals the amount of injected indicator divided by the concentration of indicator in plasma.

Penetrates blood plasma
Passes to interstitial fluid (ISF)
Passes to intracellular fluid (ICF)
Examples: Deuterium oxide (heavy water), Tritium oxide, Antipyrine or aminopyrine

Movement of water from an area of low solute concentration to high solute concentration.
OR From high water concentration to low water concentration.
A specialized type of simple diffusion.
ICF (Intracellular Fluid) calculated indirectly (TBW - ECF)
ISF (Interstitial Fluid) calculated indirectly (ECF - IVF)

Equal to osmotic force
Stops osmosis
Measured in mmHg
Depends on the number of particles (not size or mass), not on the size or mass of molecules.
Mole = molecular weight in grams
Osmole = number of particles in one mole
Osmolarity = number of osmoles per liter of water
Osmolality = number of osmoles per kilogram of water
Tonicity = Osmolality of solutions relative to plasma
Osmolarity of ICF = Osmolarity of ECF = 300 mOsm/L

Charge proteins inside the cell results in more osmotically active particles in cells compared to the interstitial fluid (ISF).
Osmosis causes the cells to swell, which can lead to rupture if the Na+/K+ ATPase pump doesn't function correctly.
The Na+/K+ ATPase pump controls cell volume and pressure
The distribution of ions across the cell membrane is asymmetrical
The difference in ion charge is calculated with the Nernst equation.
Inside the cell's protein compartment (X) is more negative than the non-protein compartment (Y)
Ion movement balances concentration and electrical gradients (e.g., Cl-, K+).
More charged proteins in cells compared to the ISF create a Donnan effect on ion movement across the blood capillary.

Normal Saline (0.9% NaCl): Vehicle for parental drugs, sterile irrigation medium, electrolyte replenishment fluid, and replacement for ECF defects.
Ringer's Solution (0.6% saline): Vitro experiments on organs and tissues, muscle testing, and ECF replacement.
Tyrode's Solution (0.8% saline): Culture medium, and peritoneum irrigation.
Isotonic Solution: Contains the same concentration of solute and water as plasma, preventing water movement and maintaining cell size.

Higher water concentration than plasma, lower solute concentration.
Water moves from solution into cells, causing them to swell and potentially rupture.
Examples: 0.33%, 0.225%, and 0.45% saline.
Importance: Intracellular dehydration, diabetic ketoacidosis (DKA), and hyperosmolar hyperglycemia.

Diagnoses various diseases.
Hereditary spherocytosis: RBCs are more fragile and spherical; hemolysis begins at 0.75% saline and completes at 0.5% saline.
B-thalassemia and iron deficiency anemia: RBCs are more rigid; hemolysis begins at 0.4% or 0.3% saline.
Sickle cell anemia: RBCs are very rigid; hemolysis begins at 0.1% saline.
Factors affecting fragility: RBC surface area to volume ratio (S/V)
Benefits of biconcave shape: Increased surface area, flexibility (capillary squeezing), greater volume capacity (CO2 transport).