Sodium and Water Balance Flashcards
how would you work out the concentration of sodium ions
mmol Na / H2O in litres
what 2 factors imbalancing the sodium equation are the causes of hyponatraemia?
too little sodium OR
too much water
what 2 factors imbalancing the sodium equation are the causes of hypernatraemia?
too much sodium OR
too little water
where is ADH made?
posterior pituitary
which part of the pituitary gland has its own blood supply?
posterior
below what level is sodium a big problem?
120mmol/l
symptoms of low sodium?
DEHYDRATION nausea altered consciousness confusion vomiting fitting
when could sodium levels be serious when they are at a normal level?
if they have fallen rapidly
most common biochemical abnormality?
hyponatraemia
what are the 2 main fluid compartments of the body?
extracellular intracellular
what is the extracellular fluid compartment made up of?
plasma
interstitial fluid
how big is the ICF compared to the ECF?
double the size
what compartment is water confined to?
none
what happens to the compartments when water is lost from the body?
the loss is distributed through all compartments
what effect does water loss have on the body and why?
not very symptomatic because water is spread through all compartments
how much sodium is in the ECF?
140mmol/l
how much sodium is in the ICF?
4mmol/l
how much potassium is in the ICF?
140mmol/l
how much potassium is in the ECF?
4mmol/l
main aim of the sodium potassium pump?
confine sodium to the ECF and potassium to the ICF
what does the body do if ECF volume is too high?
kidneys excrete more sodium so you lose water too
how are sodium and water related?
water follows sodium everywhere
what may be the only sign of hyponatraemia caused by excess water?
peripheral oedema due to water moving into the ICF
how is hyponatraemia caused by too little sodium treated?
IV saline or sodium PO
how is hyponatraemia caused by too much water treated?
fluid restriction
activity of what hormone controls sodium movement?
mineralocorticoids (cortisol and aldosterone)
what would happen to sodium if mineralocorticoid activity was low?
sodium loss
what would happen to sodium if mineralocorticoid activity was too high?
sodium retention
what would happen to eater if mineralocorticoid activity was low?
would lose water
what hormone controls water?
ADH
what kind of stimuli cause the release of ADH?
osmotic and non osmotic
what does ADH do to the renal tubules?
causes them to reabsorb water
what would your urine look like if you had alot of ADH?
concentrated urine
what kind of osmolality would concentrated urine have?
high
what kind of osmolality would dilute urine have?
low
how does ADH cause water reabsorption?
countercurrent multiplication
which limb of the loops of henle is permeable to water?
descending
what is the only part of the loops of henle that does not extrue NaCl?
descending
why is the ascending limb of the loops of henle impermeable to water?
it extrudes NaCl so it stops water going out with it
what do the loops of henle extrude water into?
ICF
what concentrations are the mediullary ICF and the loops of henle before any gradient is established?
both 300 milliosmoles/l
when will the ascending limb of the loop of henle stop releasing NaCl?
when the ICF is 200 milliosmoles more concentrated than the ascending limb’s fluid
when will the descending limb of the loop of henle stop releasing water?
until the osmolarities of the fluid in the descending limb and the ICF become equal
name some non osmotic stimuli of ADH?
hypovolaemia/hypotension
pain
nausea/vomiting
most common reason for having too much water in the body?
SIADH (failure to excrete water)
most common reason for having too little sodium in the body?
increased Na loss
what tissues is Na most commonly lost from?
adrenals
kidney
gut
skin eg burn
most likely patients to get SIADH?
post op patients
above what sodium level is considered to be serious?
> 160mmol/l
symptoms of hypernatraemia?
vomiting
nausea
fitting
main causes of hypernatraemia?
usually because of too little water:
h20 loss via diabetes insipidus OR
decreased H2O intake in extremes of age
how would you know a patient has hyponatraemia from Na loss and not H2O increase?
if they are dehydrated and “dry”
what happens when Na is low in SIADH?
retains water
what should you give if hypernatraemia is caused by low water?
give water
what should you give if there is too little sodium?
loop diuretic
how does oedema cause electrolyte retention
decreased protein hydrostatic/oncotic balance disrupted RAAS switched on = electrolyte uptake ADH retention
cause of addison’s disease?
adrenal insufficiency so can’t make steroids = no mineralocorticoid activity
why can’t addisons disease patients retain sodium?
dont have mineralocorticoids
main clinical feature of addisons disease patients?
dehydration
dizziness/hypotension
why do addisons disease patients get hypotension?
too much fluid lost from ECF
main cause of hypernatraemia by too much water
ADH secreted in repsonse to non osmotic stimulus so get water retention
