Formatives Review Flashcards
What two things happen when the macula densa senses increases in Na+?
1) afferent constriction through adenosine
2) decreased renin (don’t want more Na+ absorption)
tubuloglomerular feedback
macula densa senses increased Na+ which leads to a decrease in RPF and decrease in GFR
tubuloglomerular feedback effect on K+/H+ secretion
tubuloglomerular feedback decreases RAAS
we also know this state has more Na+
this leads to more K/H+ secretion
What happens to glomerular hemodynamics when you constrict the efferent arteriole?
Increase pressure of GC which increases GFR
You also decrease RPF
this leads to overall increase in filtration fraction
Filtration fraction formula
FF = GFR / RPF
How do you calculate clearance of a substrate?
Cx = V * Ux / Px
(make sure you make V in mL / min)
(normally given 24 hr urine volume)
How do you determine ECF? If ECF is elevated, what does this indicate?
ECF is determined by physical exam
If ECF is elevated, TBNa and TBW are elevated as well
HOWEVER, you need to check if TBNa has increased more than TBW to determine free water state
What is true if TBNa has increased more than TBW?
there is a deficit of free water
normally occurs in hypernatremia
What is true of free water in hyponatremia?
there is normally an excess of free water
Do thiazides impair concentration or dilution of urine?
they impair urinary dilution
(this can lead to hyponatremia)
Do loop diuretics effect urinary concentration or dilution?
they effect both
since they effect both, their effects largely cancel out
How do thiazides increase water reabsorption?
prostaglandin-mediated effect in the collecting duct
In a steady state, what is overall true?
urinary excretion should equal intake
What is true in the short term (before steady state is reached) of secreted sodium vs. intake sodium in diuretic use?
when you first start diuretics, you secrete a little more sodium than you take in
What is true of urine osmolality and urine sodium in SIADH?
urine osmolality is high (ADH working)
urine sodium is high
What happens to BP in hyperaldosteronism?
BP increases due to the increase in ECF expansion from increased Na/H2O reabsorption
How do you calculate free water deficit?
0.6 * weight * (serum Na - 140 / 140)
Does high or low plasma tonicity increase ADH?
high plasma tonicity
What is the target rise in PNa in a patient with chronic hyponatremia?
4-6 mEq/L increase per 24 hrs
Why do we give Ca2+ if there are EKG changes with hyperkalemia?
to stabilize the membrane potential
What do carbonic anhydrase inhibitors do?
they prevent reabsorption of HCO3-
How does increased serum bicarb affect potassium?
more H+ secreted into blood to stabilize bicarb
this leads to more K+ intracellularly and hypokalemia
What does liver failure result in in regard to BUN?
decreased BUN as liver can not produce urea
What marker of GFR isn’t as affected by muscle mass?
cystatin C
Effects of NSAIDs on loop diuretics
they compete for the same transporter that secretes loops into the lumen
therefore, NSAIDs lead to loop diuretic resistance
Why should you avoid NSAIDs with ACE/ARBs?
they can drop the GFR too low
NSAIDs constrict afferent which decreases GFR
ACE/ARBs prevent constriction of efferent which also decreases GFR
What is ACE/ARB effect on potassium levels? How?
ACE/ARB also block aldosterone (since they block AG II)
this leads to decreased K+ secretion and hyperkalemia
How do thiazide / loop diuretics cause metabolic alkalosis?
increased Na+ delivery to the collecting duct results in increased secretion of H+
What is the only location in nephron that has a brush border?
the proximal tubule
What are aquaporin 1 channels?
proximal tubule
thin descending limb
*these areas are always permeable to water
What capillaries supply the nephron?
vasa recta / peritubular capillaries
these capillaries shoot off the efferent arteriole
What is the thin descending tubule epithelium ?
Simple squamous
What is the thick ascending tubule epithelium ?
cuboidal epithelium
lots of tight junctions
low water permeability
List the glomerular capillary filtration barrier from inside out:
fenestrate capillary endothelium
glomerular basement membrane
podocyte (visceral epithelial cell)
What are proximal tubular cells closely associated with? Why?
Closely associated with peritubular capillaries so that reabsorbed solute/water can easily go back into bloodstream
What happens when afferent arteriole is constricted to FF?
GFR and RPF both proportionally decrease so there is no change in filtration fraction
What happens to afferent/efferent arterioles in massive fluid loss?
afferent dilates and efferent constricts
want to maximize GFR
Myogenic response
renal afferent arterioles contract in response to increased stretch (BP)
Ca2+ is released which triggers contraction
Where is ADH released from?
posterior pituitary
Hyperaldosterism has what effect on bicarb?
more H+ secreted = more bicarb reabsorbed into body
Where is sodium not reabsorbed?
descending limb of loop of Henle