USMLE Step 1 Renal quiz with complete solutions |Latest 2023/2024

USMLE Step 1 Renal quiz with complete solutions |Latest 2023/2024 anatomy of bowmans capsule -- kidney and ureters are retroperitoneal ureters are BEHIND vas deferens, BEHNID uterine artery water distribution in body compartments -- ... glomerular filtration barrier components -- Fenestrated capillary endothelium (size barrier) Fused basement membrane with heparan sulfate (negative charge barrier) Epithelial layer consisting of podocyte foot processes THE BASEMENT MEMBRANE LAYER IS LOST IN NEPHROTIC SYNDROME - LOST CHARGE BARRIER -- albuminuria, hypoproteinemia, generalized edema, and hyperlipidemia BM = type IV collagen, made by visceral epithelial/podocyte renal clearance + GFR -- CL = UV/P in mL/min NL ~ 100 mL/min creatinine moderately overestimates GFR (some secretion) inulin accurately measures GFR in pregnancy and early diabetic nephropathy -- INCR in Cr CL in elderly and acute/chronic renal dz -- DECR in Cr CL effective renal plasma flow (ERPF) -- CL = UV/P use PAH as proxy ERPF can be estimated using PAH CLEARANCE bc it is both FILTERED and actively SECRETED (CARRIER MEDIATED TRANSPORT) in the proximal tubule + ALL PAH entering the kidney is EXCRETED -- typically underestimates renal plasma flow by 10% RBF = RPF/(1 - Hct) filtration fraction + load -- FF = GFR/RPF NL ~ 20% filtered load = GFR x plasma concentration modulators of afferent + efferent arteriole -- ... effect of plasma protein concentration on GFR, FF -- incr [plasma] = decr GFR, decr FF decr [plasma] = incr GFR, incr FF reabsorption + secretion calcs -- excretion rate = U x V filtered load = GFR x [plasma] reabsorption = filtered - excreted secretion = excreted - filtered glucose clearance -- AT NORMAL PLASMA CONCENTRATIONS GLUCOSE IS COMPLETELY REABSORBED IN PROXIMAL TUBULE BY Na/glucose COTRANSPORT DIABETES (~160) -- GLUCOSURIA all transporters fully saturated at 350 AA clearance -- Na mediated transport in PROXIMAL TUBLE COMPETITIVE INHIBITION between AAs -- PROTEINURIA when overloaded HARTNUPs DZ = NEUTRAL AA TRANSPORTER DEFICIENCY - TRYPTOPHAN TRANSPORTER in kidney -- CANT RESORB NEUTRAL AA's - TRYPTOPHAN -- CANT MAKE 5HT, MELATONIN, NIACIN/NAD+ TRYPTOPHAN DEFICIENCY -- PELLAGRA membrane channels in proximal tubule -- Early proximal tubule - contains brush border Reabsorbs all glucose and AA and most of the bicarbonate, Na, Cl, and water ISOTONIC absorption Secretes NH3, buffer for secreted H+ PTH - inhibits Na+/PO4 cotransport -- PO4 excretes ATII - stimulates Na/H+ exchange -- Na + H2O reabsorption (CONTRACTION ALKALOSIS).