102814 dry lab Flashcards
urine flow rate equals
urine volume/time of collection
renal clearance of a substance equals
Cx= Ux * UF / Px
Ux= urine concentration of X UF= urine flow rate Px= plasma concentration of X
free water clearance equals
UF - Cosm
excretion rate of X equals
Ux * UF
Ux= urine concentration of X UF = urine flow rate
acetazolamide
carbonic anhydrase inhibitor that inhibits Na reabsorp in prox tubule
acetazolamide’s effect on urine pH
pH becomes more basic (because bicarbonate is excreted)
if urine flow doesn’t change for 2 hours and then starts to increase, what do you suspect?
there’s two counteracting agents like water and ADH
if free water clearance becomes more positive by a lot, what do you suspect?
probably with taking a lot of free water so likely to be H2O or beer. beer inhibits ADH, so more positive free water clearance is probably from beer
what should happen with taking in beef broth?
you need to get rid of more Na than water, so free water clearance should become more negative
Na excretion should increase
what should happen with taking in a 30 mM sodium bicarbonate soln?
pH should increase
it’s 60 mM concentration in osmolarity, which is much lower than blood-so receiving a lot more H2O than solute. you need to get rid of extra water, so should have more positive free water clearance than an agent like acetazolamide that acts on proximal tubule which is isoosmotic
fractional excretion of a substance =
urine excretion rate of substance/filtered load of glomerulus
it’s a measure of tubular fxn
as tubular fluid moves from beginning to end of proximal tubule, creatinine concentration will
increase
glomerulotobular balance
tubules reabsorb fixed percentage of filtered load. if filtered load increases, tubules will tend to still reabsorb the SAME percent
which is usually higher: Uosm or Posm
Uosm
free water clearance value is usually
negative
pressure natriuresis
kidneys respond to change in BP by excreting sodium instead of reabsorbing it
stimulation of renal sympath nerves will
increase sodium reabsorption
constrict blood vessels
retain sodium and fluid to prevent loss
decrease GFR (constrict vessels)
GFR changes how in relation to serum creatinine?
as serum creatinine increases-at the lower end of serum creatinine, decreases in serum creatinine will cause larger changes in GFR
equation for calculating GFR from serum creatinine
100/serum creatinine
how can creatinine clearance be calculated to assess GFR?
UV/P
Cockcroft Gault eqn
how can serum creatinine based GFR prediction be inaccurate?
extremes of age
BMI
diff in muscle mass (if pt is very heavy, will underestimate the GFR)
what happens with ECF contraction/volume depletion?
decreased effective circulating volume
baroreceptor activation
increased sympath tone
see slide-angiotensin II, aldosterone, ADH(baroreceptor)
in volume depletion, roles of angiotensin II and aldosterone?
angiotensin II likely has greater role because in proximal tubule, whereas aldosterone is in cortical collecting duct
endocrine fxns of kidney
renin
erythropoetin
1,25 dihydroxyvitamin D (made in proximal tubule cells)
chronic kidney disease produces what effects on calcium and phosphate
increases serum phosphorous (increased phosphorous retention)
decreases 1, 25 D (calcitriol)
both of these changes lead to decreased serum Ca
all of these changes lead to increased PTH, leading to increase bone turnover and extraosseous calcification
