Department of physiology Shenyang Medical College1 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 Protein Glucose RBC H2OH2O Minerals Urea glomerular filtration reabsor ption

杨宇 Department of physiology Shenyang Medical College 3 Test of Filtration Fluid In the Bowman`s capsule Filtration is the ultrafiltration fluid of palsma. CompositionPlasma (g%)Initial urine Protein70.0micro amount Glucose1.0 Amino acids0.5 Minerals7.0 H2OH2O Urea0.3

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

杨宇 Department of physiology Shenyang Medical College 6 The Physical Barrier The endothelium of the capillary: Perforated by thousands of small holes called “ fenestrae ”, diameter is about nm.

杨宇 Department of physiology Shenyang Medical College 7 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.

杨宇 Department of physiology Shenyang Medical College 8 The Physical Barrier Footlike processes ( Podocytes ) : The foot processes are separated by gaps called “ slit pores ”, diameter is about 4-11 nm.

杨宇 Department of physiology Shenyang Medical College 9 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

杨宇 Department of physiology Shenyang Medical College 12 Filtration Membrane Damaged or Injuryed Filtration Membrane Damaged or Injuryed Acute glomerulonephritis → → obstruction of glomerular capillary → → filtration membrane area ↓ → → amount of filtrate fluid ↓ → → oliguria

杨宇 Department of physiology Shenyang Medical College 13 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.

杨宇 Department of physiology Shenyang Medical College 14 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

杨宇 Department of physiology Shenyang Medical College 17 Forces Controlling Filtration Glomerular capillary hydrostatic pressure:P GC Bowman's space hydrostatic pressure:P BS Glomerular capillary colloid osmotic pressure:  GC Effective filtration pressure =P GC – (P BS +  GC )

Forces Controlling Filtration

杨宇 Department of physiology Shenyang Medical College 20 Factors Influence GFR (1)P GC 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 )

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.

杨宇 Department of physiology Shenyang Medical College 22 Factors Influence GFR (2)P Bc is Bowman's space hydrostatic pressure -It is increased by constriction of the ureters. -Increases in P B c cause decreases in net filtration pressure and GFR. - In normal condition, the Bowman’s space pressure (P BC ) do not change significantly except in renal disease or obstruction of the urinary tract by urinary stone or tumor.

杨宇 Department of physiology Shenyang Medical College 23 Factors Influence GFR (3) π GC : 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 π GC 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.

杨宇 Department of physiology Shenyang Medical College 24 Factors Influence GFR (4) Renal Blood Flow : change the “ balance point of filtration”

杨宇 Department of physiology Shenyang Medical College 25 Factors Influence GFR (5) K f : filtration coefficient GFR K f = ———— is a constant EFP (effective filtration pressure) Related to filtration membrane’s permeability and area.