RENALDr;

bashardoust

Glomerular Filtration

• Renal blood flow = 1.2 L/min• Renal plasma flow = 700 ml/min (60 % of RBF)• GFR = 125 ml/min = 180 L/day filtered plasma

– Filtered fraction = GFR RPF = 125 700 = 20%

• Urine output = 1 ml/min or 1500 ml/day = 1% of filtered plasma

Renal Anatomy• Functional unit is the nephron

– Approximately 1.25 million/kidney– 80% are cortical – short loop of Henle– 20% are juxtamedullary – loop of Henle projects

into medulla– Cortical nephrons only dilute urine– Juxtamedullary nephrons dilute and concentrate

urine

• Functions of nephron– Glomerular filtration– Tubular reabsorption– Tubular secretion

Filtration, Reabsorption, Secretion

A: filtered, no reabsorption or secretion - inulin, creatinine

B: filtered, some reabsorption - electrolytes

C: filtered, complete reabsorption - glucose, amino acids

D: filtered, plus additional secretion - K+, H+

Anatomy:

J.G.App.

Afferent Arteriole Efferent

Cap. loops

DCT

Glomerular Filtration:

L.R.IL.D.L.R.E

Foot Process

Podocyte

(Visceral epithelium)

GBMGBM

Glomerular Capillary LumenGlomerular Capillary Lumen

Bowman’s Capsule SpaceBowman’s Capsule Space

+

Collagen IVLamininFibronectinEntactinetc.

BLOODBLOOD

ProteinsProteins3.6nm/3.6nm/70,000MW70,000MW

Plasma - Plasma - ProteinsProteins

FILTRATEFILTRATE

Table 47-2. Laboratory Findings in Acute Renal Failure

Index PrerenalAzotemia

Oliguric AcuteRenal Failure

BUN/PCr Ratio >20:1 10-15:1

Urine sodium (UNa), meq/L <20 >40

Urine osmolality, mosmol/L H2O >500 <350

Fractional excretion of sodium <1% >2%

FENa = UNa * PCr * 100

PNa * UCr

Urine/plasma creatinine (UCr/PCr) >40 <20

NOTE: BUN, Blood urea nitrogen; PCr, plasma creatinine; UNa, urine sodium concentration; PNa, plasma sodium concentration; UCr, urine creatinine concentration.