Kidney diseases and failure

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Repetition of physiology

Regulation of water, electrolyte (blood pressure!) and acidobasic balance

Removal of metabolic endproducts, foreign substances and toxins (not everything – small molecules soluble in water)

Urea (carbamid), creatinine, uric acid Endocrine function (renin and erytropoetin)

2*800 000 – 1 200 000 nephrons Cortex and medulla

Special blood supply : 1000 ml/min = 20% CO

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Filtration and clearance

Blood (plasma) flow and filtration is stable and independent on blood pressure (GFR = 2 ml/s, 120 ml/min, 180 l/d)

Filtration fraction: Ratio between filtration and plasma flow : 120/600 = 0,20 (20 %)

Clearance: Virtual amount of urine, which is cleared from a substance in a time unit

Clearance is dependent on Filtration Tubular secretion and resorbtion

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Proteinuria

Glomerular membrane = ultrafilter, the result is a solution similar to plasma but less protein

The pore diameter allows the passage of molecules < 30 kDa and the basal membrane has a negative charge

But it is10 g/d, in filtrate and only 25 mg in urine Variable according to physical activity and

postural position

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6 MEMEASUREMENTASUREMENT and and ASSESMENTASSESMENT OF OF GFRGFR

Clearance of a substance which is only filtered = GFR

Clearance = [U]/[P]*V

[U][P] = cc in urine and plasma

V = volume of urine

Clearance = volume of plasma cleared

8.5.2010nefro.ppt

7 MEMEASUREMENTASUREMENT and and ASSESMENTASSESMENT OF OF GFRGFR

Clearance = [U]/[P]*V

[U][P] = cc in urine and plasma

V = volume of urine

Clearance = volume of plasma cleared

Inulin (polysaccharide)

Endogenous creatinine – not very exact

Problems – 24h urine, method and secretion

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8 ASSESMENTASSESMENT OF GFROF GFR

Assesement from serum creatinine

[Krea]*GFR = k

GFR = k/[Krea]

It is not so simple

Creatinine syntheis is not stable: Age, muscle mass, meat in food…

Not only filtered

But cheap and simple

Theoretical association between serum creatinine and GFR

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0

200

400

600

800

1000

1200

1400

1600

1,5 1,3 1,1 0,9 0,7 0,5 0,3 GFR, ml/min  

UriSed

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12Classification of National Kidney Foundation USA, 2005

Grade GFR, ml/s Prevalence, USA, %

SR

1 > 1,5 or normal GFR

3,3 165 000

2 1,0 – 1,49 slightly GFR

3,0 150 000

3 0,5 – 0,99 midlle GFR

4,3 210 500

4 0,25 – 0,49

severe GFR

0,2 10 000

5 < 0,25 Kidney failure

0,2 10 000