10.30: Renal Review Flashcards
What is special about flow of blood in kidney?
Only place in body where blood goes from artery, to capillary and back to artery
Where does filtrate go after it leaves glomerulus?
Bowmans capsule
Is there much protein in healthy urine?
- No, nearly none is filtered
- Most that is filtered is reabsorbed
- Protein in urine sign of pathology
What is Tamm horsfall protein?
- Makes up majority of protein seen in healthy urine
- Serves to prevent clot formation
Main factor impacting glomerular filtration?
Hydrostatic pressure in the capillary
How is RPF estimated?
- PAH clearance
- Nearly all that enters renal circulation is excreted
RPF = clearance PAH
RBF equation?
RBF = RPF / (1-hematocrit)
What is the filtration fraction?
FF = GFR./ RPF
*Normally 125/625 ml /min ~20%
What happens in decreased RPF?
- RAS system constricts efferent arteriole
- Increase hydrostatic pressure in capillary
- Maintains GFR increase FF
What do prostaglandins do to afferent?
Dilate increasing RPG and GFR
What do NSAIDs do to afferent arterial?
- Constrict it
- Can cause renal failure
What does angiotensin do to efferent arterial?
Constricts
How does kidney autoregulate in increased systemic BP?
- Constricts afferent
RAS steps?
- Renin converts angiotensinogen to angiotensin I
2. ACE converts I to II
How do ACE inhibitors work?
- Prevent angiotensin from constricting efferent arteriole
- Decreases GC pressure to protect kidney
What do dihydropyridine Ca antagonist drugs do?
- Very effective at lowering BP
- But abolish autoregulation of kidney so renal hypertension can occur
Best way to measure GFR? How is it normally measured?
- Inulin
- Freely filtered and neither reabsorbed or secreted
- ***However, measured creatinine clearance is most often used
Creatinine clearance calculation?
Clearance = (urine [] * urine flow rate) / plasma []
Why is creatinine good measure?
- Byproduct of muscle breakdown
- In steady state, production = excretion
What is eGFR?
Estimated GFR
What is required for eGFR?
- Steady state level of plasma creatinine
- Cannot be used if renal function is rapidly changing
What is relationship between creatinine clearance and plasma creatinine?
- Inversely proportional (C= UV/P)
- If clearance is 100 and plasma is 1
- If plasma 2, clearance would be 50
- If 4, then 25
What is creatinine clearance good example of?
GFR
Cockroft Gault equation?
(140 - age * weight kg) / 72 * plasma Cr
- ***Multiply by .85 if female
- Gives us creatinine clearance
When is eGFR applicable?
Only if serum creatinine is stable
What happens in CDK to creatinine?
- Exponential increase in plasma Cr with time
What happens in AKI to creatinine?
- Linear increase
- Drops back to normal if function restored
What does amount of Cr in a healthy person depend on?
Directly proportional to muscle mass
What is fractional excretion?
- Amount of substance excreted in urine related to amount filtered by kidney
- FE = Amount excreted / amount filtered
What is FENa equation?
FENa = (UNa/PNa) * (PCr/Ucr) * 100
What is FENa in healthy person?
1%
What happens to FENa in decreased GFR?
- Increases
- As long as there is not edema present
Where are bulk of solutes reabsorbed?
Prox tubule
What happens in loop of henle?
Water goes out diluting filtrate
What does ADH do?
Water resorption in collecting ducts
What does tubular [] > plasma [] mean?
Item is being secreted
What is proximal tubule dysfunction called?
Fanconi syndrome
What is fanconi Syndrome?
- Prox tubule disorder with decreased resorption
- Glycosuria
- Hypo P, K
- Metabolic acidosis: Bicarb is buffer
- Proteinuria
What is loop dysfunction called?
- Bartter’s syndrome
- Salt wasting
- Hypokalemia
- Metabolic acidosis
What is bartter’s syndrome?
- Loop dysfunction
- Salt wasting
- Hypokalemia
- Metabolic acidosis
- **Loop diuretics cause same problems
What does distal dysfunction cause?
Gitelman’s syndrome
What is Gitelman’s syndrome?
- Distal disfunction
- Hypokalemia, Mg, Ca
- Thiazides case the same
Where is angiotensinogen made?
Liver
Where is ACE present?
Mostly lung but kidney too
What does angiotensin II do?
- Vasoconstric
- Activate aldosterone
Where is EPO made?
Kidney
Where is Vitamin D activated?
Kidney
What is orthostatic hypertension indicative of?
Volume depletion
What should FENa be if volume depleted?
Low
