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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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MEASUREMENT and ASSESMENT OF
GFR
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
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MEASUREMENT and ASSESMENT OF
GFR
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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ASSESMENT OF 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
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Theoretical association between
serum creatinine and GFR
1600
1400
1200
1000
800
600
400
200
0
1,5
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1,3
1,1
0,9
0,7
0,5
0,3 GFR, ml/min
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UriSed
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Classification of National Kidney Foundation USA, 2005
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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
nefro.ppt
8.5.2010