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Formation of Urine : Process of Glomerular Filtration
Dr Sunita Mittal
AA EA
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▪To understand the function of the filtration membrane
▪To define glomerular filtration rate, renal blood flow
▪To measure glomerular filtration rate, renal blood flow
Learning Objective
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1. Glomerular filtration-
2. Tubular processing-
a. reabsorption &
b. secretion)
3. Urinary excretion-
.
Basic Processes required for Formation of Urine
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Site of filtration - Glomerulus
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Physiology of Glomerular filtration
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Glomerular filtrate
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Glomerular ultrafiltrate-protein & cellular elements free blood
Important contributors:
1. Filtration Membrane (Barrier)
2. Unique pressure dynamics
within the glomeruli
https://www.researchgate.net/publication/285735121_Regulation_of_renal_hemodynamics/figures?lo=1
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1) Endothelial cells layer of the capillary,
2) Basement membrane and
3) Epithelial cells (podocytes) – surrounding outer surface of cp
basement membrane.
Glomerular Filtration Membrane / Barrier
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▪The capillary endothelium has thousands of small holes called
fenestrae
▪But loaded with negative charged glycoproteins
Glomerular Filtration Barrier – Cp Endothelial layer
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Glomerular Filtration Barrier - basement membrane
▪The surrounding basement membrane - is a porous meshwork of
proteins – ▪ contain type IV collagen and proteoglycan fibrillae.
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▪The long finger like processes of the podocytes interdigitate to
cover the basement membrane and are separated by apparent
gaps called filtration slits.
Glomerular Filtration Barrier – Podocytes Layer
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Glomerular Filtration Barrier – Podocytes Layer
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GFB restricts the filtration of substances on the basis of
Size & Electrical charges
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Applied - Kidney diseases (Nephropathies) and
Filtration Barrier
Nephrotic syndrome
Glomerulonephritis
Hypertension
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▪Dia of afferent arteriole > efferent glom arteriole –
▪Capillary bed between two arteries–
2.Unique pressure dynamics within the glomeruli
aff
ere
nt
eff
ere
nt
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Glomerular Filtration Rate
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Glomerular Filtration Rate
120 ml/min
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RBF
≈1100 ml/min,
RBF is important as -
Renal Blood Flow
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Renal Clearance/ Renal plasma clearance
10 L
This much volume of fluid
is free of drug in unit time.
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Relative clearances of substances
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Estimation of GFR by
Renal Plasma Clearance
GFR:
Substance: Inulin
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RBF:
Substance: PAHA
Estimation of RBF by
Renal Plasma Clearance
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Estimation of GFR– Renal Plasma Clearance
GFR
(Cin)=Uin X V / Pin
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RBF:
RBF =RPF/0.9 (1-hematocrit)
Estimation of GFR and RBF – Renal Plasma Clearance
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Clinical problem – TO calculate GFR :
Estimation of GFR and RBF – Renal Plasma Clearance
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Problem-RBF: Calculate RBF of a patient
Estimation of GFR and RBF – Renal Plasma Clearance
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Filtration Fraction = GFR/RPF=125/625=0.20
Filtration Fraction
20%
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Increase in the filtration fraction -
Decrease in the filtration fraction -
Filtration Fraction
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Glomerular filtration rate (GFR) is an important clinical indicator
of status of kidney function.
Applied Physiology
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Serum Creatinine:
normal value =
Applied Physiology
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Significant points in lecture
Filtration barrier, Slit diaphragm, disorder in nephrotic syndrome
Uniqueness of pressure dynamics in glomeruli
GFR, RBF
Substances of measurement and clearance
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MCQ
renal clearance of a substance is the VOLUME OF PLASMA from which that
substance is completely removed (cleared) per unit time.Inn that case following is
a false statement:
a) Renal clearance = GFR → when No net reabsorption, secretion
b) Renal clearance = GFR → when No net reabsorption
c) Renal clearance > GFR → Net secretion
d) Renal clearance < GFR → Net reabsorption
If a normal person has a plasma creatinine level 1 mg/dl that later
becomes 2 mg/dl, what happens to GFR?
Ans: 50% of the value of GFR at1 mg/dl.
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