Physiology Flashcards
general osmolality of cell fluid?
300
tonicity is dependant on what 2 factors?
osmalarity
ability of a solute to cross the cell membrane
- i.e 2 solutions of the same osmolarity have different ability to cross the membrane due to different structure (i.e urea vs sucrose)
300mM urea is hypotonic to RBCs while 300mM sucrose is isotonic to RBCs, why is this?
cell membrane of red blood cells are very permeable to urea due to urea transporters
as urea moves, it leaves water behind (outside the cell), this creates an osmotic gradient and water moves into the cell
tonicity vs osmolarity?
tonicity = the effect osmolarity has on the cell volume
osmolarity <300?
hypotonic
osmolarit >300?
hypertonic
osmolarity of 300?
isotonic
water makes up what percentage of total body weight in males and females?
males = 60% females = 50% (due to higher amount of fat which contains little water)
total body water consists of what 2 fluid compartments?
intracellular fluid (67% of total body water) extracellular fluid (33% of total body water)
extracellular fluid contains what?
plasma (20%)
interstitial fluid (80%)
lymph and transcellular fluid (negligible)
how is the volume of a fluid compartment measured?
using tracers and obtaining the distribution volume of these tracers
give examples of tracers and how theyre used
ECF = inulin
plasma = labelled albumin
total body water = 3H2O
TBW = ECF + ICF
how do tracers work?
add known quantity of tracer to the body
take a sample of body fluid and measure the concentration of tracer in the sample
distribution volume = quantity of tracer/concentration of tracer in sample
what contributes to water input?
fluid intake
food intake
meatbolism
what contributes to water output?
insensible - skin - lungs sensible loss - sweat - faeces - urine
sensible vs insensible water loss?
sensible = regulatory mechanisms in place in the body to control water loss
greatest water loss from the body?
urine (1.5L per day)
the kidneys compensate for increased water loss by reducing urine output but they cant turn of urine production completely, why is this?
some waste products can only be secreted in solution
effect of kidneys on osmolarity?
kidneys have an effect on ion concentrations
ion compensation of extracellular fluid?
like sea water
- high sodium
- high chloride
- low potassium and bicarbonate
ion compensation of intracellular fluid?
low sodium and chloride
higher potassium and bicarbonate
what separates the plasma and the intracellular fluid (of skeletal muscle) and how does ion composition compare?
interstitial fluid between capillary wall and plasma membrane of skeletal muscle cell
similar ion composition to plasma
osmotic concentrations of ECF and ICF?
the same
300mosmol/L
because changes in solute concentrations lead to immediate changes in water distribution, the regulation of fluid balance and electrolyte balance are tightly intertwined
what is fluid shift?
movement of water between ICF and ECF in response to an osmotic gradient (water moves without salt)