Physiology 1: body fluid compartments Flashcards
what is osmolarity
concentration of osmotically active particles in a solution (osmol/l)
what does high osmolarity mean
lots of ions that drive water osmosis eg a concentrated solution (usually weak salts)
what 2 factors must be known to calculate osmolarity
molar concentration and number of osmotically active particles
what would the osmolarity of 100mM of MgCl2 be
moles = 100mM, active particles = 3: 3x100 = 300mosmol/l
what is the difference between osmolality and osmolarity
osmolality is units /kg of water vs osmolarity is units /l
what is the osmolarity of most body fluids
300mosmol/l
what is tonicity
the effect an osmotic solution has on a cell
what effect does a hypotonic solution have on a a cell
hypotonic = not many active particles eg very dilute - causes water to diffuse into cell to higher concentration and cell to swell/ Burst (lysis)
what effect does a hypertonic solution have on a a cell
hypertonic = lots of active particles eg very concentrated - causes water to diffuse out of cell to higher concentration and cell to shrink
what is an isotonic solution
osmolarity is same inside and outside the cell
what % of males and females are water
males 60% and women 50%
what are the 2 major compartments total body water exists as
intercellular fluid (66%) and extracellular fluid (33%)
what is extracellular fluid made of
interstitial fluid 80% / plasma 20% (liquid component of blood) / negligible lymph and transcellular
what different tracers are used to calculate how much water are in each compartment: TBW, ECF and plasma
TBW: titrated water 3H2O / ECF: inulin / plasma: labelled albumin
how would you use a tracer to figure out total volume of compartment (volume of distribution)
1) add specific dose of tracer eg D=42mg to unknown water volume (V) 2) mix and take a small sample volume eg 5ml 3) measure concentration and scale back eg 0.005mg/5ml = 1mg/l 4) insert into calculation V = D/C eg 42/1 = 42L
what 3 ions mostly make up the osmolarity of the ECF
Na, Cl and HCO3
what 2 ions mostly make up the osmolarity of the ICF
K and Mg (slightly negative)
what effect would an increased ECF osmotic concentration have on the ICF
water would move down it’s concentration gradient out of the ICF and into the ECF to maintain the osmolarity of both
what are the 3 main challenges to fluid concentration
gain or loss of water / gain or loss of Na / gain or loss of isotonic fluid eg NaCl
what is an electrolyte
a salt that dissociates in a solution to give free ions eg NaCl –> Na+ (ECF) and Cl- (ICF)
what is the importance of sodium in the water balance
determines ECF osmolarity and therefore volume - too much = hypertonic and too little = hypotonic
what is the importance of the potassium balance in the body
establishes membrane potential and ICF osmolarity - too much = muscle weakness and paralysis (cell to negative so no depolarisation and APs) and also cardiac irregularities
