Salt and Water disorders Flashcards
total body water equation?
TBW= .6L/Kg…so in a 60 Kg dude, it is 36L
.5 L/Kg in women
Plasma osmolality equals what?
two times the Na concentration + glucose + BUN
Explain the difference between extracellular fluid volume and effective circulating blood volume
ECFV is the total volume in the extracellular space. This can be independent of effective blood volume. Effetive circulating blood volume is determined by cardiac output and venous resistance. In diseases like cirrhosis or CHF, ECFV can be normal or high and ECBV is low.
What intrarenal system senses reduced blood volume?
Macula Densa
What cells is renin secreted by?
Juxtaglomerular cells
RAAS?
Renin ANgiotensin Aldosterone System….controls SODIUM BALANCE> NOT WATER
What does renin do directly>
cleaves angiotensin I to Angiotensin II
What does ANgiotensin II do?
increases vasoconstriction (raises bp) and stimulates aldosterone which increases sodium reabsorption
ANP is actually important
true
What does ANP do?
the exact opposite of angiotensin II and aldosterone…it vasodilates and increases Na excretion
What kind of tonicity does the body want?
ISOtonicity…if serum sodium is high or low (osmolarity is high or low) body responds to it.
Where is the thirst center?
Third ventricle
What stimulates the thirst center?
Increased extracellular fluid osmolarity
What is the serum osmolarity threshhold for activation of the thirst center?
2mEq/L
What is the only hormone that plays a role in water reabsorption?
AVP- vasopressin
Is hyponatremia a water problem or a sodium problem?
Its tricky, although it sounds like a sodium problem, hyponatremia is really a water imbalance. There is low sodium CONCENTRATION…this is because there is excess water.
Low extracellular fluid volume is related to what?
Low sodium content
What is hypovolemic hyponatremia
Low sodium concentration associated with low ECFV.
Clinical signs of sodium depletion
1) decrease in blood pressure (esp orthostatic bp)
2) Poor skin turgor
3) Disproportionate increase in BUN
4) reduced urine sodium
What does SIADH mean>
this is euvolemic hyponatremia due to water autonomous or altered regulation of vasopressin release. Basically, SIADH means altered vasopressin realease …too much(Vasopressin is an antidiuretic)
Clinical signs of SiADH>
Decreased serum osmolarity, inappropriate urine concentration (its not maximally dillute like it should be), clinical euvolemia,
