Fick's Principle in Volume Compartment Dynamics

Fick's Principle

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

Properties of Indicator

• Inert: Does not react with the body.
• Non-toxic: Does not harm the body.
• Well-mixed: Distributes evenly throughout the compartment.
• Easily measurable: Concentration can be measured easily
• Unchanged: Not altered by the body tissue.
• Does not affect: Doesn't change water or substance distribution in tissues.

TBW Indicator

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

ECF Indicator

• Penetrates blood plasma
• Passes to interstitial fluid (ISF)
• Does not pass to intracellular fluid (ICF)
• Examples: Inulin, Sodium thiocyanate

IVF Indicator

• Does not penetrate blood plasma
• Does not pass to interstitial fluid (ISF)
• Does not pass to intracellular fluid (ICF)
• Examples: Evan's blue dye, Fibrinogen and albumin with radioactive iodine

Osmosis

• 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)

Osmotic Pressure

• 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

Gibbs Donnan Equilibrium

• 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.

Physiological Solutions

• 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.

Hypotonic Solution

• 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.

Hypertonic Solution

• Higher solute concentration than plasma, lower water concentration.
• Water moves from cells into solution, causing cell shrinkage (crenation).
• Examples: 3%, 5%, and 10% dextrose in water
• Importance: Isolate living tissues

Osmotic Fragility Test

• 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).

This quiz explores Fick's Principle and the properties of indicators used in measuring body fluid compartments. It covers different types of indicators such as Total Body Water (TBW), Extracellular Fluid (ECF), and Intracellular Fluid (ICF) indicators with examples. Test your understanding of how these indicators function and their relevance in physiological studies.