Water and Electrolyte Balance Flashcards
What proportion of total body water (TBW) of ~40L is located inside cells as intracellular fluid (ICF)?
25L exists as ICF, with the remaining 15L exists as extracellular fluid
What proportion of the ~15L of ECF is the plasma in the intravascular compartment?
3L of ECF is plasma
The remaining 12L is interstitial fluid, within the tissues but outside the cells.
What is the dominant cation in the ICF?
Potassium, K+
What is the dominant cation in the ECF?
Sodium, Na+
What are the major ICF anions?
Phosphate (HPO42-) and negatively charged proteins are the major intracellular anions
What are the major ECF anions?
Chloride (Cl-) and Bicarbonate (HCO3-) are the major extracellular anions
What is the difference between interstitial fluid and plasma with regards to protein concentrations?
Only plasma has significant protein concentrations, interstitial fluid contains very little protein
How is the difference in protein content between plasma and interstitial fluid maintained?
The impermeability of the capillary wall to protein
How does the difference in protein concentration between plasma and interstitial fluid affect the fluid balance?
The greater colloid osmotic (or oncotic) pressure within the intravascular compartment favours fluid retention within the circulating plasma
Where is the greatest [K+]?
ICF or ECF?
The greatest [K+] is in the ICF
Where is the greatest [Na+]?
ICF or ECF?
The greatest [Na+] is in the ECF
Where is the greatest [Cl-]?
ICF or ECF?
The greatest [Cl-] is in the ECF
Where is the greatest [HCO3-]?
ICF or ECF?
The greatest [HCO3-] is in the ECF
Where is the greatest [HPO42-]?
ICF or ECF?
The greatest [HPO42-] is in the ICF
What is the major force governing the differences in cation concentrations between ICF and ECF?
The major force is the sodium-potassium pump (Na,K-activated ATPase) which, dependent on ATP, removes 3 Na+ ions from the cell, and draws 2 K+ ions into the cell
