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Department of physiology Shenyang Medical College 1
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
杨宇 Department of physiology Shenyang Medical College 2
Section 2 Glomerular Filtration Section 2 Glomerular Filtration
Protein
Glucose
RBC
H2O
Minerals
Urea
glomerular filtration
reabsorption
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Test of Filtration FluidTest of Filtration FluidIn 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
The Glomerular Gapillary The Glomerular Gapillary Membrane ( filtration membrane )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 The Glomerular Gapillary Membrane ( filtration membrane )( filtration membrane )
The physical barrier
The electric barrier
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The Physical BarrierThe 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 BarrierThe 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 BarrierThe 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 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.
Protein filtration:
influence of negative charge on glomerular wall
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Filtration Membrane Filtration Membrane Damaged or InjuryedDamaged or Injuryed
Acute glomerulonephritis
→ → obstruction of glomerular
capillary → → filtration
membrane area ↓ → →
amount of filtrate fluid ↓
→ → oliguria
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Two Important Concepts 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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The glomerular filtration fraction
The glomerular filtration rate
The total renal plasma flow
=
125ml/min
660ml/min≈ 20%
=
FF: The Glomerular Filtration Fraction
Fraction is the filtration rates as percentage of the total renal plasma flow that passes through both kidneys.
Effective Filtrated Pressure
Figure 26.10a, b
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Forces Controlling FiltrationForces Controlling FiltrationGlomerular capillary hydrostatic
pressure:PGC
Bowman's space hydrostatic
pressure:PBS
Glomerular capillary colloid osmotic pressure: GC
Effective filtration pressure=PGC – (PBS + GC )
Forces Controlling FiltrationForces Controlling Filtration
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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 )
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.
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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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