ANATOMY & PHYSIOLOGY
OF KIDNEY
RENAL ANATOMY
RENAL PHYSIOLOGY
Proximal convoluted tubule
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 function
• Most frequently performed test of renal function.
• 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)/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)
Inulin GFR
• Gold Standard
• Complex 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
•
99mTc-DTPA 51Cr-EDTA
• Single bolus injection with blood taken for
isotopic counting at intervals
Creatinine Clearance
• Timed urine collection for creatinine
measurement (usually 24h)
• Blood sample taken within the period of
collection.
Problems: • Practical problems of accurate urine collection
and volume measurement
Plasma Creatinine Concentration
Difficulties: • Production determined by muscle massrelated to age, sex and weight.
• 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 glomerulus
Constant production rate by all nucleated cells
No known extra-renal excretion routes
Not influenced by muscle mass, diet or subjects
sex
Blood urea level
• Untill 75 % renal function is lost
• Metabolism of proteins & synthesised in liver
• May be rised when
– High protein intake
– Excessive protein catabolism – steroids ,tetracyclines
– Absorption of blood from GIT
• Low level –reduced dietary intake
Renal blood flow
• PAH clearance
• Normal values 500-600 ml /min
Urinary Concentration
• Urine specific gravity
• Water deprivation test
Urinary Acidification
Done in suspected cases of RTA
• Urine pH
• Sod. Bicarbonate loading test
• Ammonium chloride loading test
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