ANATOMY & PHYSIOLOGY OF KIDNEY

RENAL ANATOMY

RENAL PHYSIOLOGY

Proximal convoluted tubule

Loop of henle

Distal convoluted tubule

Na+ K+ H+ ====

EVALUATION OF RENAL FUNCTION

Measurement of Glomerular Filtration Rate (GFR ) GFR is essential to renal functionGFR is essential to renal function Most frequently performed test of renal function.Most frequently performed test of renal function. Measurement is based on concept of clearance: -Measurement is based on concept of clearance: - “The determination of the volume of plasma from which a substance is removed by glomerular filtration during it’s passage through the kidney”

Determination of Clearance Clearance = (U xV)/PClearance = (U xV)/P Where U is the urinary concentration of substance x V is the rate of urine formation (mL/min) P is the plasma concentration of substance x Units = volume/unit time (mL/min) Units = volume/unit time (mL/min)

Inulin GFR Gold StandardGold Standard Complex procedureComplex procedure –Bolus dose followed by constant infusion –Timed urines, with bloods taken midpoint of collection periods, for inulin assay. –GFR is taken as the mean for each period.

Isotopic GFR 99m Tc-DTPA 51 Cr-EDTA 99m Tc-DTPA 51 Cr-EDTA Single bolus injection with blood taken for isotopic counting at intervalsSingle bolus injection with blood taken for isotopic counting at intervals

Creatinine Clearance Timed urine collection for creatinine measurement (usually 24h)Timed urine collection for creatinine measurement (usually 24h) Blood sample taken within the period of collection.Blood sample taken within the period of collection. Problems: - Practical problems of accurate urine collection and volume measurementPractical problems of accurate urine collection and volume measurement

Plasma Creatinine Concentration Difficulties: - Production determined by muscle mass- related to age, sex and weight.Production determined by muscle mass- related to age, sex and weight. Concentration inversely related to GFR.Concentration inversely related to GFR. –Small changes in creatinine within and around the reference limits = large changes in GFR

Cystatin-C Small size - freely filtered at glomerulusSmall size - freely filtered at glomerulus Constant production rate by all nucleated cellsConstant production rate by all nucleated cells No known extra-renal excretion routesNo known extra-renal excretion routes Not influenced by muscle mass, diet or subjects sexNot influenced by muscle mass, diet or subjects sex

Blood urea level Untill 75 % renal function is lostUntill 75 % renal function is lost Metabolism of proteins & synthesised in liverMetabolism of proteins & synthesised in liver May be rised whenMay be rised when –High protein intake –Excessive protein catabolism – steroids,tetracyclines –Absorption of blood from GIT Low level –reduced dietary intakeLow level –reduced dietary intake

Renal blood flow PAH clearancePAH clearance Normal values ml /minNormal values ml /min

Urinary Concentration Urine specific gravityUrine specific gravity Water deprivation testWater deprivation test

Urinary Acidification Done in suspected cases of RTA Urine pHUrine pH Sod. Bicarbonate loading testSod. Bicarbonate loading test Ammonium chloride loading testAmmonium chloride loading test

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