The document discusses various factors affecting glomerular filtration rate (GFR) and renal function tests, including the components and functions of nephrons, the impact of arterial diameter and blood pressure on nephron function, and processes like reabsorption and clearance. It outlines specific tests to assess glomerular and tubular functions, measurement techniques for substances like glucose, and methods for calculating GFR using inulin and creatinine. Additionally, it covers the conditions required for substances used to evaluate GFR and renal plasma flow, emphasizing the significance of the clearance ratio in determining the renal handling of substances.

1. Factors affecting GRF
Dr Shamshad

2. Objectives
 Describe the components and functions of nephron
 Discuss how arterial diameter affects nephron function
 Discuss how blood pressure affects nephron function
 Explain the process of reabsorption
 Explain the role of carriers in glucose reabsorption
 Identify the actions of ADH and aldosterone on solute
reabsorption and water uptake prerequisite materials and
equipment.

3. Glomerular Function Test
Renal clearance tests
Tests for glomerular functions
Tests for tubular function: uremia
Others
Renal Function Test done :
To assess the functional capacity of the
kidneys
To detect the renal impairment as

4. Renal clearance tests
Glomerular functions Test
• Inulin clearance
• Creatinine clearance
• Other : IVP
• Artiography
• USG
• Isotope perfusion studies
• Renal biopsy
Test for tubular functions
• PAH clearance
• Urea clearance
• PSP excretion test
• Measurement of water
reabsorption
• Other: micropuncturing
• Stop flow technique
• Microcryoscopic studies
• Microelectrode studies

5. Definition : Clearance of a certain substance is the volume of
plasma cleared from this substance per unit time (minute).
Calculation: According to law of conservation of mass:
Ux*volume of urine/minute=GFR*Px
C=excretion rate/plasma concentration
The mass of substance (X) extracted from plasma / minute =
concentration of substance (X) in plasma (PX) X the volume of
plasma which is cleared from this substance / minute (CX).

6. Glucose clearance
 All the filtrated glucose is reabsorbed at plasma concentration
below 250mg/dl.
 Clearance of glucose is zero below 250mg/dl.
 Glucose appear in urine at about 250mg/minute.
• The reabsorption becomes saturated at plasma concentration
above 350mg/dl.
• This is maximum transport rate (TM) =375mg/min.

7. The point at which the glucose
appear in urine is threshold .
and transport maximum is called
splay.
The renal handling of the
glucose curve,
the Tm is approached gradually
along a curve,
rather than abruptly
with a sharp deflection
The curve is called as splay.
Transport maximum of glucose

8. Measurement of reabsorption
• Rate of reabsorption of a solute Ts
• Is the difference between the product of GFR and substance
in plasma and the rate of its excretion
• Ts=(GFR*Ps)-(Us*vol)
• Unit: mg/minute

9. Measurement of Secretion
The rate of secretion of a solutes Ts, is the difference between
the rate of excretion Us*V, and the rate of filtration, GFR*PS
Ts=(Us*V)-(GFR*Ps)m/minute.

10. According to substance selected; clearance may be used
for:
1- Measurement of glomerular filtration rate (GFR):
Clearance of inulin or creatinine.
2- Measurement of renal plasma flow (RPF):
Clearance of PAH.
3- Measurement of reabsorptive capacity of renal
tubules:
Transport maximum of glucose (TMG).
4- Measurement of secretory capacity of renal tubules:
Transport maximum of PAH (TMPAH).
5-

11. 5- Mode of handling of substance by the kidney:
Clearance ratio and fraction excretion.
6- Assessment of diluting capacity of the kidney:
Free water clearance.
7- Assessment of concentrating capacity of the kidney:
Free water reabsorption

12. Measurement of GFR
Substance used to measure GFR should apply
the following conditions:
1- Non-toxic.
2- Does not affect GFR or RPF.
3- Not metabolized by the body or the kidney.
4- Freely filtered: of small molecular weight
and not bound to plasma proteins
5- Neither reabsorbed nor secreted.
6- Accurately measured in plasma and urine.

13. Two substances were used:
1:Inulin (Exogenous):
Polymer of fructose.
Given by IV drip & not orally as it is digested in the intestine.
GFR = Cin = 125 ml./min.
Advantages:
Accurate hence it is used for experimental studies.
Disadvantages:
Exogenous (need a method of administration)

14. 2:Creatinine (endogenous):
End product of creatine metabolism in skeletal muscles.
- GFR = CCr = 140 ml./min.
Advantage: Endogenous.
Disadvantage:
Slightly secreted in PCT .Certain drugs affect the secretion .
Hence GFR measured by this method is 10% higher than GFR
measured by inulin clearance.
Clearance Ratio:

15. Measurement of renal blood flow:
Substance used to measure renal plasma flow should apply the
following conditions:
1- Non-toxic.
2- Does not affect GFR or RPF.
3- Its unbound fraction is freely filtered.
4- Completely secreted not reabsorbed.
5- Accurately measured in plasma and urine.
Substance used is Para amino hippuric acid (PAH):
RPF = CPAH =
Some plasma supplies the non-functioning kidney structures, which
include capsule, pelvis and perinephric fat.

16. • Plasma concentration of substance
Px*clearance of subx Cx=Ux*V
• GFR=Cx=Ux*V/Px
• Effective renal plasma flow=GFR
• Effective RBF=ERBF=Cx=EFPF/1-Hct
• Renal blood flow=RBF=ERBF/Extraction ratio
• Extraction ratio=Atrial x-Venous x/Atrial x

17. Def.:
Ratio between clearance of substance and clearance of
inulin.
Clearance ratio =
Significance:
Detect the mode of handling of the substance by the kidney.
Since inulin is neither reabsorbed nor secreted:
If CR = 1 the substance is neither reabsorbed nor secreted.
If CR > 1 the substance is partially reabsorbed.
If CR < 1 the substance is partially secreted.
If CR = 0 the substance is completely reabsorbed