RENAL CLEARANCE AND RENAL BLOOD FLOW

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RENAL CLEARANCE AND RENAL
BLOOD FLOW
Dr.Mohammed Sharique Ahmed Quadri Al Maarefa
Colege
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Objective

• Describe the concept of renal plasma clearance
• Use the formula for measuring renal clearance
• Use clearance principles for inulin, creatinine
  etc. for determination of GFR
• Use PAH clearance for measuring renal blood flow
• Outlines the factors affecting the renal blood
  flow .

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Plasma clearance

• Definition
• Volume of plasma completely cleared of a
  particular substance by kidneys per minute
• (not the amount of the substance removed)
• Varies for different substances, depending on how
  the kidneys handle each substance
• Unit- ml/min

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• EQUATION FOR RENAL CLEARANCE
• Cx (U)x X V
• (P)x
• Where -
• Cx Clearance(ml/min)
• (U)x Urine concentration of the
• substance(mg/ml)
• V Urine flow rate (ml/min)
• (P)x Plasma conc of the substance(mg/ml)

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• If substance is filtered , not reabsorbed or
  secreted , its plasma clearance rate equals GFR

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• Clearance of Various Substances
• Albumin 0 normally albumin is not filtered
  across the membrane
• Glucose 0 normally filtered glucose is
  completely reabsorbed back into the blood stream
• Inulin is equal to the GFR.(Glomerular Marker)
  Inulin is a Fructose polymer freely filtered
  across the membrane and neither reabsorbed nor
  secreted.
• PAH Para Amino Hippuric Acid( other organic
  acids).Has highest clearance since it is both
  filtered and secreted.

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• Clinically it is not convenient to use inline
  clearance to maintain a constant plasma
  concentration it must be infused continuously
  throughout measurement
• Creatinine clearance is used as a rough estimate
  of GFR

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• CLEARANCE RATIO
• Clearance of any substance (x) compared with
  clearance of Inulin C x (
  glomerular marker)
• C inulin
• C x 1 (filtered neither reabsorbed nor
  secreted)
• C inulin
• C x lt 1 (substance is not
  filtered/filtered reabsorbed)
• C inulin
• C x gt 1 (substance is filtered as well as
  secreted )
• C inulin

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Sample problem

• In a 24hr period, 1.44 L of urine is collected
  from a man receiving an infusion of inulin.
• In his urine, the inulin is 150mg/ml, and Na
  is 200 mEq/L.
• In his plasma, the inulin is 1mg/mL, and the
  Na is 140mEq/L
• What is the clearance ratio for Na, and what is
  the significance of its value?

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Renal plasma flow can be estimated from the
clearance of Para-amminohippuric acid

• (Ficks Principle) The amount of a substance
  entering the organ is equal to the amount of
  substance leaving it( assuming that substance is
  neither synthesisized nor degraded by the organ
  ).
• by measuring the amount of a given substance
  taken up per unit of time and dividing this value
  by the arteriovenous difference for the substance
  across the kidney.
• Since the kidney filters plasma, the renal plasma
  flow equals the amount of a substance excreted
  per unit of time divided by the renal
  arteriovenous difference as long as the amount in
  the red cells is unaltered during passage through
  the kidney.
• Any excreted substance can be used if its
  concentration in arterial and renal venous plasma
  can be measured and if it is not metabolized,
  stored, or produced by the kidney and does not
  itself affect blood flow.

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• PAH CLEARANCE
• PAH acid is an organic acid which is almost 90
  cleared in 1 circulation through the kidneys
  since it is both filtered and secreted by the
  tubules.
• neither metabolized nor synthesized by the
  kidneys.
• PAH does not alter the RPF.
• No other organ extracts PAH
• Hence clearance of PAH gives the effective Renal
  Plasma Flow (EPRF)

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Use of PAH Clearance to Estimate Renal Plasma Flow
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To Calculate Actual RPF , One Must Correct for
Incomplete Extraction of PAH( extraction ratio)
APAH 1.0
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• Renal Clearance gives an indication of the
  functioning of the kidneys.

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Name Equation Units
Clearance Ux V Px mL/min
GFR U inulin x V P inulin mL/min
Clearance Ratio C x C inulin None
Effective Renal Plasma Flow U (PAH) x V P (PAH) mL/min
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• REGULATION OF RENAL BLOOD FLOW
• RBF (Q)
• is directly proportional to the pressure gradient
  (?P) between the renal artery and the renal vein
• Is inversely proportional to the resistance(R) of
  the renal vasculature
• (Q) ? P
• R
• The major mechanism of changing Renal blood flow
  is by changing Afferent or Efferent Arteriolar
  resistance.

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• 1) SYMPATHETIC NERVES AND CIRCULATING
  CATACHOLAMINES
• Both afferent and efferent arterioles are
  innervated by sympathetic nerves that act via a1
  receptors to cause vasoconstriction.
• However ,since far more a1 receptors are present
  on Afferent arterioles, increased sympathetic
  stimulation will cause a decrease in both RBF
  GFR.

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• 2) ANGIOTENSIN II
• This is a potent vasoconstrictor. However
  Efferent arteriole is more sensitive to
  Angiotensin II. Hence low levels of Angiotensin
  II causes increase in GFR while high levels of
  Angiotensin II will decrease GFR. RBF is
  decreased.
• 3) PROSTAGLANDINS
• PGE 2, PGI 2 are produced locally in the
  kidneys cause vasodilation of both afferent
  efferent arterioles.
• This effect is protective for renal blood flow ,
  it modulates the vasoconstriction produce by
  sympathetic angiotensin-II
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• 4)DOPAMINE
• At low levels Dopamine dilates Cerebral,
  Cardiac, Splanchnic Renal arterioles and
  constricts Skeletal Muscle and Cutaneous
  arterioles. Hence low dose Dopamine can be used
  in the treatment of hemorrhage .

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• AUTOREGULATION OF RENAL BLOOD FLOW
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• Myogenic theory
• 2. Tubuloglomerular feedback by Juxta Glomerular
  Apparatus (JGA)

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References

• Human physiology by Lauralee Sherwood, seventh
  edition
• Text book of physiology by Linda .s
  contanzo,third edition
• Text book physiology by Guyton Hall,11th edition