Download Section 2 Glomerular Filtration

Section 2 Glomerular Filtration
Urine forming begins with filtration from the
glomerular capillaries into Bowman`s
capsule of a large amount of fluid that is
virtually free of protein.
Most substances in the plasma, except for
proteins, are freely filtrated so that their
concentration in the glomerular filtrate in
Bowman`s capsule are almost the same as in
the plasma
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Section 2 Glomerular Filtration
glomerular filtration
Protein
RBC
Glucose
H2 O
Minerals
Urea
reabsor
ption
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Test of Filtration Fluid
In the Bowman`s capsule Filtration is the
ultrafiltration fluid of palsma.
Composition
Plasma (g%)
Initial urine
Protein
70.0
micro amount
Glucose
1.0
1.0
Amino acids
0.5
0.5
Minerals
7.0
7.0
H2O
920
980
Urea
0.3
0.3
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The Glomerular Gapillary
Membrane ( filtration membrane )

Is similar to that of
other capillaries,
excepted that it has
three major layers
forming the physical
barrier.
 Being negatively
charged coated to
forming the
electric barrier.
The Glomerular Gapillary
Membrane ( filtration membrane )
The physical barrier
The electric barrier
The Physical Barrier
 The
endothelium of the capillary:
Perforated by thousands of small
holes called “ fenestrae ” , diameter
is about 70-90 nm.
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The Physical Barrier
 Basement
membrane:
Which consists of a meshwork of
collagen and proteoglycan fibrillae,
diameter is about 2-8 nm, however,
diameter of plasma albumin is 3.6
nm.
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The Physical Barrier
 Footlike
processes ( Podocytes ) :
The foot processes are separated
by gaps called “ slit pores ”,
diameter is about 4-11 nm.
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The Electric Barrier
 The
endothelial pores, basement
membrane and surface coat of the
podocytes contain negatively
charged glycoproteins which impede
the passage of negatively
charged plasma proteins.
 Such as plasma albumin.
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Protein filtration:
influence of negative charge on glomerular wall
Filtration Membrane
Damaged or Injuryed

Acute glomerulonephritis
→ → obstruction of glomerular
capillary → → filtration
membrane area ↓ → →
amount of filtrate fluid ↓
→ → oliguria
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Two Important Concepts

GFR: The quantity of glomerular
filtrate formed per minute by both
kidneys. The GFR in an average-sized
man is approximately 125 ml/min.
 This value can
using calculates
the clearance of
inulin in kidneys,
which is the golden
standard, as we discuss later.
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FF: The
Glomerular Filtration Fraction
Fraction is the filtration rates as
percentage of the total renal plasma flow
that passes through both kidneys.
The glomerular filtration rate
The glomerular
filtration fraction
=
The total renal plasma flow
125ml/min
≈
=
20%
660ml/min
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Effective Filtrated Pressure
Figure 26.10a, b
Forces Controlling Filtration
 Glomerular
capillary hydrostatic
pressure:PGC
 Bowman's space hydrostatic
pressure:PBS
 Glomerular capillary colloid osmotic
pressure: GC
Effective filtration pressure=PGC – (PBS + GC )
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Forces Controlling Filtration
Factors Influence GFR
(1)PGC is glomerular capillary
hydrostatic pressure:
BP fluctuation between in 80~180mmHg
→→ maintained the stable of RBF →→ the
RBF does not vary in the denervated →→
GFR stabilize ( Autoregulation )
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 BP
fluctuation between in 80~180mmHg
→→ maintained the stable of RBF →→
the RBF does not vary in the denervated
→→ GFR stabilize ( Autoregulation )
 When BP the lowing 80mmHg in the
hypovolumic shock, out the
autoregulation , oliguria appearanced
because of GFR decreasing.
 But the lowing 40 ~ 50 mmHg , GFR is
zeor ,anuria can be seen.
Factors Influence GFR
(2)PBc is Bowman's space hydrostatic pressure
-It is increased by constriction of the ureters.
-Increases in PBc cause decreases in net filtration
pressure and GFR.
- In normal condition , the Bowman’s
space pressure (PBC) do not change
significantly except in renal disease
or obstruction of the urinary tract
by urinary stone or tumor.
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Factors Influence GFR
(3) πGC : glomerular capillary colloid osmotic
pressure.
It normally increases along the length of the
glomerular capillary because filtration of water
increases the protein concentration of glomerular
capillary blood.
It is increased by increases in protein concentration.
Increases in πGC cause decreases in net filtration
A decrease in plasma protein concentration due to
intravenous infusion of a large volume of saline will
decrease intracapillary osmotic pressure leading to an
elevated GFR.
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Factors Influence GFR
(4) Renal Blood Flow : change the “ balance
point of filtration”
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Factors Influence GFR
(5) Kf: filtration coefficient
GFR

Kf = ———— is a constant
EFP (effective filtration pressure)
 Related
to filtration membrane’s
permeability and area.
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