The first step in urine formation is filtration of large amounts of fluid through the glomerular capillaries into Bowman’s capsule—almost 180 L/day. Most of this filtrate is reabsorbed, leaving only about 1 liter of fluid to be excreted each day, although the renal fluid excretion rate is highly variable, depending on fluid intake. The high rate of glomerular filtration depends on a high rate of kidney blood flow, as well as the special properties of the glomerular capillary membranes.

1. GLOMERULAR
FILTRATION
By
Prof. Dr. Nusrat Tariq
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2. .
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3. LEARNING OBJECTIVES
By the end of this lecture you should be
able to:
• Define GFR
• Describe the determinants of GFR
• Explain the factors affecting GFR
• Discuss the hormones and autocoids
that affect GFR
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4. GLOMERULAR MEMBRANE
• The membrane at which filtration occurs
• It is made up of 3 layers
1. capillary endothelium
2. basement membrane
3. layer of epithelial cells (podocytes)
surrounding the capillaries
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6. Glomerular capillary membrane
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9. SELECTIVITY OF GLOMERULAR MEMBRANE
Filtration rate is inversely proportional to the
Molecular Weight. Water with highest filterability and
albumin with lowest
• The pore size is 8 nanometer
• Albumin is also not filtered because of its negative
charge repulsed by the negatively charged
glomerular capillary proteoglycans
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11. GLOMERULAR FILTRATION
.
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12. GLOMERULAR FILTRATION
RATE (GFR)
Glomerular Filtration Rate is defined
as volume of filtrate formed each
minute by both Kidneys.
Normal/ Average Adult GFR =
120 - 125 ml/ min or 180L/day
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13. GLOMERULAR FILTRATE
• The filtrate is devoid of proteins
and RBC
• The concentration of filtrate is
similar to ?????.
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14. GLOMERULAR FILTRATE
• The filtrate is devoid of proteins
and RBC
• The concentration of filtrate is
similar to plasma.
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15. RENAL BLOOD FLOW
• Renal blood Flow is 22% of the
cardiac output or 1100 ml/min
• Renal plasma flow is 55% of the
RBF approximately 600ml/min
• GFR is 20% of the renal plasma
flow
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16. FILTRATION FRACTION
• Filtration fraction is the fraction
of plasma which is filtered.
• Filtration fraction =GFR/RPF
=125/600
=0.2
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17. DETERMINANTS OF
THE GFR
GFR = Kf × Net filtration pressure
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18. FILTRATION COEFFICIENT
(KF)
Kf = the product of the hydraulic
conductivity and surface area of
the glomerular capillaries.
GFR = Kf × Net filtration pressure
Kf =????
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19. FILTRATION COEFFICIENT
(KF)
GFR = Kf × Net filtration pressure
Kf = GFR/Net filtration pressure
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20. NET FILTRATION
PRESSURE
forces causing filtration by the
glomerular capillaries
??????
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22. NET FILTRATION PRESSURE
• sum of capillary hydrostatic pressure minus
the colloid osmotic pressure plus the
bowman's capsular pressure
• 60-(32+18)=10mmHg
• Capillary hydrostatic pressure is the outward
force (60 mmHg)
• Colloid osmotic and bowmans pressure are
inward forces (32mmHg+18mmHg)
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23. DETERMINANTS OF GFR
GFR=Kf x net filtration pressure
Net filtration pressure depends on three
forces
1. capillary hydrostatic pressure
2. capillary colloid osmotic pressure
3. bowman's capsular pressure
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24. 1)Increased Glomerular Capillary Filtration
Coefficient (Kf) Increases GFR
2) Increased Bowman’s Capsule Hydrostatic
Pressure Decreases GFR
3) Increased Glomerular Capillary Colloid
Osmotic Pressure Decreases GFR
4) Increased Glomerular Capillary Hydrostatic
Pressure Increases GFR
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25. 1)Increased Glomerular Capillary
Filtration Coefficient Increases GFR
Kf = GFR/Net filtration pressure
Total GFR = 125 ml/min
Net filtration pressure = 10 mm Hg
The normal Kf is = 12.5 ml/min/mmHg of
filtration pressure.
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26. 1)Increased Glomerular Capillary
Filtration Coefficient Increases GFR
Some diseases lower Kf by
 Reducing the number of functional
glomerular capillaries(thereby reducing the
surface area for filtration)
 Increasing the thickness of the glomerular
capillary membrane and (reducing its
hydraulic conductivity).
Example: chronic, uncontrolled hypertension
and diabetes mellitus
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27. 2-INCREASED BOWMANS
HYDROSTATIC PRESSURE INCREASES
GFR
Stones that lodge in the urinary tract
obstruct outflow of the urinary tract
and raise the Bowman’s capsule
pressure causing reduction of GFR.
.
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28. 3) Increased Glomerular Capillary Colloid
Osmotic Pressure Decreases GFR
Filtration fraction = GFR/Renal plasma flow
= (125ml/m)/(650ml/m)
= 0.2
Increases in the filtration fraction
increases the plasma colloid osmotic
pressure as the proteins are
concentrated in the glomerular capillary
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29. 4) Increased Glomerular Capillary
Hydrostatic Pressure Increases GFR
Glomerular hydrostatic pressure is determined
by three variables:
(1) arterial pressure,
(2) afferent arteriolar resistance, and
(3) efferent arteriolar resistance.
• Constriction of afferent arterioles reduces GFR.
• Modest efferent constriction raises GFR, but
• Severe efferent constriction tends to reduce
GFR.
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31. Others Factors Affecting the GFR
• Changes in renal blood flow
• Changes in systemic blood pressure
• Afferent or efferent arteriolar constriction
• Edema of kidney inside tight renal capsule
• Changes in concentration of plasma proteins:
dehydration, hypoproteinemia, etc (minor factors)
• Changes in glomerular capillary permeability
• Changes in effective filtration surface area.
• Contraction of mesangial cells: Decreases GFR by
reducing the Kf due to reduction in surface area for
filtration
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32. Agents Causing Contraction or Relaxation
of Mesangial Cells.
• Contraction Relaxation
• Endothelins ANP
• Angiotensin II Dopamine
• Vasopressin PGE2
• Norepinephrine cAMP
• Thromboxane A2
• Histamine
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33. Factors which can decrease GFR
• Kf in DM, HTN, renal diseases
• PB in urinary tract obstruction
• GC oncotic pressure due to RBF or in plasma
proteins
• PG
1. ABP
2. angiotensin II
3. sympathetic stimulation leading to
vasoconstiction  RBF in afferent arteriole
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34. Factors That Can Decrease the Glomerular Filtration Rate
(GFR)
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35. b)Hormonal and Autacoid that influence Renal Circulation
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