Body Fluids Flashcards
TBW
About 60% of body weight
ICF
40% of body weight
2/3 TBW
ECF
20% of body weight
1/3 of TBW
ISF + blood plasma
About 1 L in humans
ISF
15% of body weight
75% of ECF
Blood plasma
5% of body weight
Contains various proteins while other compartments don’t
25% of ECF
Hematocrit
Proportion of blood volume made up by RBC
About 45% in men, 40% in women
Total blood volume calculation
Plasma volume + (TBV * Htc)
OR
TBV = .75 x body weight
Indicator dilution method
Putting dyes that isolate to one compartment to measure volume
Volume calculation (w/ dye)
Amount of dye (- excreted amount) / diluted concentration of dye
TBW indicators
Heavy water
Antipyrine
ECF indicators
Na, mannitol, inulin, l-iothalamate
Plasma
I-albumin
Evans blue dye
Ions higher extracellularly
Na (!), Cl, Ca, HCO3
Ions higher intracellularly
K (!), Mg
Calcium
Very low intracellular, highest concentration gradient, would flow from ECF to ICF
pH gradient
ICF is more acidic, 2x [H+]
ICF = 7.0
ECF = 7.4
Protein distribution
Should be no proteins ISF, only ICF and plasma
Electroneutrality
Each compartment is electroneutral - # of cations = anions but can be different across membrane
Hyperosmotic to ICF
Cell shrinks because water flows out
Idealized semi-permeable membrane
Membrane is permeable to water but not molecules so only osmosis
Isoosmotic to ICF
No change
Hypoosmotic to ICF
Cell swells because water flows in
Osmolarity of ICF and ECF
EQUAL, around 280-300 mOsm/L
Osmolarity equation
Molarity x number of molecules
Molarity = mass / MW
Effective osmolarity
Only considers impermeant solutes
Osmotic pressure
Water moves to more solute concentrated side - if you want it to stop, apply osmotic pressure to that side
Tonicity vs osmolarity
Tonicity only considers impermeant solutes/effective osmolarity
Plasma oncotic pressure (πc)
Pushes water into plasma/capillaries
Caused by proteinsin plasma
Plasma hydrostatic pressure (Pisf)
Pushes fluid into capillaries
Hydrostatic pressure in capillaries (Pc)
Pushes fluid into ISF
Strongest force
Oncotic pressure in capillaries (πisf)
Pushes fluid into ISF
Weakest, usually ignored
Net driving force
Pc - πc - Pisf + πisf
Na-K ATPases
Maintain ion gradient
Na OUT, K in (against gradient)
Isoosmotic volume contraction
Water loss and electrolytes loss in ECF are proportional
Caused by diarrhea or vomiting
Hyperosmotic/hypertonic volume contraction
Caused by dehydration - sweating, fever, diabetes insipidus (decreased ADH, dilute urine)
Hypoosmotic volume contraction
Water loss in ECF < electrolytes loss in ECF
Caused by adrenal insufficiency, low aldosterone, very low bp, salt craving
Isoosmotic volume expansion
Proportional water and electrolytes gain in ECF
Caused by isotonic NaCl infusion
Hypoosmotic volume Expansion
Water gain > electrolytes gain
Caused by syndrome of inappropriate ADH - water retention - hyponatremia transiently
Hyperosmotic volume expansion
Water gain < electrolytes gain
Caused by hyponatremia - high NaCl intake, water retention
Hypovolemia
Loss of water - volume contraction
Increases [plasma protein] and plasma oncotic pressure
Hypervolemia
Gain of water - volume expansion
Decreases [plasma protein] and plasma oncotic pressure
SIADH
ADH causes water retention - diluted plasma, dilute ECF
Significantly increased in SIADH
Causes hypo-osmotic volume expansion
Diabetes insipidus
Extremely low ADH - dilute urine, concentrated ECF
Hyperosmotic volume contraction
Adrenal insufficiency
Aldosterone increases sodium and water in ECF
Low aldosterone - very low sodium (water follows)
Hypoosmotic volume contraction