Sodium and Water Flashcards
draw diagram of body fluid distribution
see notes
formula to calculate osmolarity
2[Na+] + glucose/18 + [BUN]/2.8
increase in osmolarity triggers….
ADH release and thirst
JGA senses what? what happens?
change in Na+ flow rates –> stim RAAS
Baroreceptors sense what? what happens?
decreased arterial pressure –> stim adrenergic pressure, stim ADH release
Atrial stretch receptors sense what? what happens?
volume expansion –> ANP release
Action of angiotensin II (3)
- direct vasoconstrictor (efferent arteriole)
- increases Na+ and HCO3- reabsorption in proximal tubule
- stim aldosterone release
Action of aldosterone
- stimulates Na+ channels in the principal cells (CD)
2. stim H+ secretion in intercalated cells
ANP
- direct vasodilator: lowers BP, afferent arteriolar dilation –> increased GFR
- stim Na+ excretion
what is the response to increased ECV?
Na+ diuresis: increased renal blood flow –> less renin
ANP
equation to estimate free water deficit
0.6wt[(Na+/140))-1]
rate of correction for a given free water deficit
Estimated water deficit/[(desired change in Na+)x2] = cc/hr
correction for hyperosmolar hyponatremia
in hyperglycemia: Na+ falls 1.6-4 mEq/L for every 100mg/dL rise in glucose
pseudohyponatremia
when lots of lipids are in the serum, get an artificially inflated total sample volume –> hyponatremia
how to calculate water excess
0.6weight(([Na+]-140)/140)
when is ADH released? name an exception
when osmolarity increases
except, decreased ECV overrides osmolar control –> sim ADH to maintain BP
when do you get low ADH hyponatremia?
- renal failure - water intake exceeds excretion as GFR falls
- primary polydipsia - excessive intake exceeds excretion
- beer potomania/”tea and toast” - take in lots of fluid but not enough osmoles to excrete large volumes of water
types of high ADH hyponatremia
- decreased ECV: volume depletion, diuretics, CHF, etc.
- reset osmostat
- SIADH
reset osmostat
some pts have a lower ADH set point than normal
no other abnormalities other than low [Na+]
no tx needed
causes of euvolemic hyponatremia
- SIADH
- hypothyroidism
- hypoadrenalism
osmotic demyelination
stroke-like syndrome of neurological deficits associated with overly rapid correction of hyponatremia
V2 antagonists - what do they do, when to use
block ADH action
useful for elevated ADH (SIADH, CHF, cirrhosis)
tx for SIADH
fluid restrict asymptomatic pts
hyperosmotic saline for symptomatic or severe
DO NOT GIVE NS
how to calculate FENa
FENa= (UnaScr)/(SnaUcr)
draw a diagram of the whole nephron!
see notes
