Regulation of ECF Volume and Water Balance Flashcards
[…] is the major effective osmole in the ECF and determines the movement of water into/out of cells
NaCl
How can you estimate the plasma osmolality (Posm) of a patient?
Measure serum [Na+] and mulitply by 2 to account for equal parts Cl- for each Na+ molecule
Ex: serum Na+ = 145 mEq / L then Posm = 290 mEq / L
When a person is hyponatremic or hypernatremic, what is driving that change in [Na+]?
Water
Too much = hyponatremia
Too little = hypernatremia
The driving force for fluids to shift between the body’s fluid compartments is driven by what?
Most important take away - WATER MOVES across the membrane, not the Na+
What if there is isoosmotic volume change? Will there be shifts between body fluid compartments?
No
IMPORTANT: Fluid shifts occur ONLY IF […] osmolality changes.
ECF
Additional questions:
- Calculate TBW and ICF, ECF volumes before infusion.
- Calculate again after infusion.
- Does plasma volume (25% of ECFV) change?
ECF
Why does water balance change body fluid osmolality?
If you were to add 1L of pure water to a person’s body (i.e. ingestion or IV infusion):
- Where is this fluid added?
- What is the effect on osmolality?
- What will be the response of the kidneys?
- ECF
- Decreased
- Decrease reabsorption of water to increase excretion of water to restore normal osmolality
If you were to remove 1L of pure water from a person’s body:
- Where is this fluid removed from?
- What is the effect on osmolality?
- What will be the response of the kidneys?
- ECF
- Increase
- Increase reabsorption of water to restore normal fluid volume and osmolality