Renal

Question 1

Equation for eRPF (effective renal plasma flow)

Answer 1

Estimated using PAH clearance:

eRPF = (urine [PAH]/plasma[PAH]) * (urine flow rate) = clearance of PAH

eRPF underestimates true RPF slightly

Question 2

Equation for renal blood flow (RBF)

Answer 2

RBF = RPF/(1 - Hct)
Usually = 20-25% of cardiac output

Question 3

Equation for plasma volume

Answer 3

PV = (total body vol) * (1 - Hct)

Question 4

Equation for GFR using inulin

Answer 4

Estimated using inulin clearance:

(urine [inulin]/plasma [inulin]) * (urine flow rate) = clearance of inulin

GFR ~ creatinine clearance.
Normal GFR ~ 100 ml/min

Same equation as eRPF using PAH clearance!

Question 5

Equation for filtration fraction (FF)

Answer 5

FF = GFR/RPF

Normal FF = 20%

Question 6

Equation for filtered load

Answer 6

Filtered load = GFR * plasma concentration

Question 7

Equation for GFR using pressures in glomerular capillaries and Bowman’s space

Answer 7

GFR = Kf ((Pg - Pb) - (onc.g - onc.b))

g & b = glomerular capillary and bowman’s space; P = hydrostatic P, onc = oncotic P

Question 8

Tuberous sclerosis

Answer 8

Tuberous sclerosis: “HAMARTOMAS” - Hamartomas in CNS/skin, Angiofibromas, Mitral regurg, Ash-leaf spots, cardiac Rhabdomyoma, (tuberous sclerosis), autosomal dOminant, Mental retardation, renal Angiomyolipoma, Seizures/Shagreen patches

Question 9

VHL disease

Answer 9

“Von HARPel-Lindau”: Hemangioblastomas in CNS, Angiomatosis (e.g. cavernous hemangiomas in skin, mucosa, organs), bilateral Renal cell carci, Pheochromocytomas

Question 10

Drugs that commonly cause acute interstitial nephritis

Answer 10

NSAIDs
Penicillins
Cephalosporins
Loop Diuretics
Allopurinol

“Lotsa Drugs Cause Acute iNterstitial nePhritis”

Question 11

Risk factors for nephrolithiasis

Answer 11

• Hypercalciuria/oxaluria/uricosuria (primary hyperPTH, crohn, gout)
• Hypocitraturia (distal RTA)
• Low fluid (dehydration), low calcium intake
• High oxalate (spinach, rhubarb), protein, Na+, fructose

Question 12

Causes of renal papillary necrosis

Answer 12

SAAD papa:
Sickle cell dz/trait
Acute pyelo
Analgesics (NSAIDs)
Diabetes mellitus

P/w gross hematuria/proteinuria from sloughed necrotic papillae; may be triggered by recent infxn or immune stimulus

Question 13

Regions of nephron most susceptible to anoxic injury

Answer 13

Acute, severe hypoxia –> cortical necrosis, with loss of the PCTs + thick ascending limb (PCT highly ATP-dependent so first signs of anoxic injury seen here)

Chronic, sub-severe hypoxia –> medullary/papillary necrosis (medulla already receives less blood supply - atrophies over time)

Question 14

Types of azotemia, BUN/Cr, FeNa/osmolarity of urine

Answer 14

Prerenal: decreased blood flow to kidneys. high BUN/Cr > 15 (15 is normal) d/t reabsorption of fluid and BUN. Tubules not dmged, so can still resorb Na and concentrate urine (Osm > 500, FeNa < 1%)

Intrarenal: can be ATN, AIN, renal papillary necrosis. BUN/Cr < 15; FeNa > 2% (decreased reabsorption of Na), low osmolarity < 250 (can’t concentrate urine)

Postrenal: outflow obstrxn (stones, BPH, neoplasia, congenital anomalies). Only occurs with bilat obstrxn or in a solitary kidney. BUN/Cr >15 acutely, then drops < 15 with long-standing obstrxn; FeNa and urine osm vary