Body Fluid compartments Flashcards
Anion gap = ?
Serum Na+ - (Cl- + HCO3-)
**essentially the difference between positive and negative charges in the plasma
**plasma is neutral due to presence of negatively charged albumin which makes up for the “gap”
Normal plasma osmolality:
~300 mM/L
Define osmolality:
total free solute (mM) / kg of solvent
Define osmolarity:
total free solute (mM) / L of solvent
Osmolarities of Plasma solutes:
Na+: 140 (mM/L)
Cl-: 105
HCO3-: 25
Urea: 6
Weak organic acids: 6
Gluc: 5 (~90 mg)
K+: 4
Ca++: 4
Mg+: 1
H2PO4-: 1
Albumin: 1
Total: 296
Interstitial fluid is plasma without____?
albumin
Under normal circumstances, capillary hydrostatic pressure is opposed equally by_________.
capillary oncotic pressure (albumin)
**both are ~25mmHg
Why is intracellular space so different in composition from vascular and interstitial space?
Only water passes freely (AQUAPORINS).
Ions controlled by ATPases.
More potassium (140 mM/L)
Less sodium (~10 mM/L)
Isosmotic refers to?
Any solution with ~300 mM/L (mOsmos)
Isotonic refers to?
Any solution that will not change the volume of the cell (contains 300 mOsmos of impermeable solute)
Isoncotic refers to:
Any solution with protein oncotic pressure of 25 mmHg
% of total body volume made up of water?
60
Approximate distribution of total body water in L for 70 kg person:
Intracellular: 28 L (66%)
Extracellular: 14 L (33%)
Interstitial: 11 L Plasma: 3 L
Total: 42 L (28+14)
Composition of normal saline:
154 mOsmol Na
154 mOsmol Cl
so this is isosmotic and isotonic – will not enter intracellular space
A few indications for NS:
DKA
Sepsis
Diarrhea (loss of Na/Cl)
Half NS distribution?
half like NS, half like H2O
Distribution of D5?
just like water
Will giving NS change the plasma Na concentration?
No
but it will increase plasma volume because Na will not distribute intracellularly
