10: Body Fluid Compartments Flashcards
Volume contraction vs expansion
Contraction: decrease in ECF (volume depletion)
Expansion: increase in ECF
How much of the body’s water is ECF vs ECF
ICF: 66%
ECF: 33%
Two portions of ECF and what separates them
Interstitial fluid (80%) + plasma (20%) - separated by capillary wall
Other fluids of the body not considered ICF or ECF
Lymph, CSF, humors of eye, serous fluid, GI secretions
60-40-20 rule of body water
- 60% of body weight is total body water
- 40% of body weight is ICF
- 20% of body weight is ECF
How is ECF an intermediary between cells and external evnironment?
All exchanges btwn cells and environment must occur thru the ECF
Only fluid that can be acted on directly to control its volume and composition
Plasma
Electrolytes vs non-electrolytes
- Electrolytes: dissociate into ions in water
2. Non-electrolytes: contain covalent bonds that prevent them from dissociating in solution - have no electrical charges
What has a greater ability to cause fluid shift - electrolytes or non electrolytes - and why?
Electrolytes - have higher osmotic power as they dissociate into at least two ions
What ions are found more in ICF vs ECF?
ECF: Na, Cl
ICF: K, PO4, more protein anions
Tonicity of a solution
The effect the solution has on cell volume - can cause it to remain the same size, swell, or shrink
NaCl concentration of an isotonic cell environment
0.85% NaCl
Predominant cation in ECF
Na
What ion ECF volume mainly regulated by?
Na
Na concentrations in ECF and ICF typically
ECF: 140 mEq/L
ICF: 5 mEq/L
Three main solutes in ECF
Na, glucose, urea
Equation for calculating serum osmolality + the “eyeball” way to do it
Osmolarity = 2(Na) + (glucose/18) + (BUN/2.8)
Eyeball: 2(Na)
X and Y axes of Darrow-Yannet diagrams
X axis: volume in L
Y axis: osmolality in mOsm/kg H2O
What does polyuria imply about water or solute diuresis or urine volume?
- Implies water/solute diuresis of 2.5-3 L/day +
2. Urine volume of 40+ mL/kg/day
Four mechanisms that cause polyuria
- Increase fluid intake
- Increased GFR (fever, hyper metabolic states)
- Increased solute output (DM, hyperthyroid, use of diuretics)
- Inability of kidney to reabsorb water in DCT (CDI, drugs, chronic renal failure)
Water diuresis
Increased water exretion without corresponding increase in salt exretion
Main causes of water diuresis
Increased intake of water, polydipsia, diabetes insipidus
Solute diuresis
Increased water excretion concurrent with increased salt excretion
Primary causes of solute diuresis
Significant increase in salt present in tubular fluid; NaCl, hyperglycemia, high protein intake, recovery from AKI
