1. Renal Physiology 5Renal Physiology 5
Dr. Bikesh Pandey

2. Regulation Of ReabsorptionRegulation Of Reabsorption

3. Reabsorption RateReabsorption Rate
• It is the rate at which Filtrates
are reabsorbed per unit time.
• More than 99 per cent of the
filtrate are normally
reabsorbed.
• It is normally 124 ml/min.

4. Reabsorption Rate (Fluid Dynamic)Reabsorption Rate (Fluid Dynamic)
Pc = Capillary hydrostatic pressure
Pif = Interstitial hydrostatic pressure
Πc = Capillary osmotic Pressure
Πif = Interstitial osmotic pressure
Kf = 12.4

5. Glomerulotubular BalanceGlomerulotubular Balance
• It is an intrinsic ability of the tubules to increase
their reabsorption rate in response to increased
tubular load.
• Mainly observed in PCT.
• Due to changes in physical forces in the tubule
and surrounding renal interstitium.

6. Glomerulotubular BalanceGlomerulotubular Balance

7. Decreased Reabsorption
to Blood From Interstitium
causes Increased “Back Leak”

8. NatriuresisNatriuresis
• It is the process of excretion of sodium in the urine.
• If “Back – leak” of Sodium increases, more sodium is
excreted in urine.
• And, if, this condition is due to increase in Hydrostatic
pressure of interstitium; we call it “Pressure
Natriuresis”
• Hydrostatic pressure of interstitium can rise due to
over-accumulation of fluid as a consequence of
decreased “Bulk Flow”

9. Pressure-DiuresisPressure-Diuresis
• Hydrostatic pressure of interstitium can
rise due to over-accumulation of fluid as a
consequence of decreased “Bulk Flow”.
• Which increases “Back-Leak” and
subsequently causes the water to be more
in tubule; causing more urine excretion
(Diuresis).

10. Hormonal Control of ReabsorptionHormonal Control of Reabsorption
• Hormones provide specificity of tubular
reabsorption for different electrolytes and
water.

11. HormonesHormones EffectEffect
Aldosterone • Increases Na+ Reabsorption
• Increases K+ Secretion
Angiotensin II •Increases Na+ Reabsorption
• Increases Water Reabsorption
ADH • Increases Water Reabsorption
ANP •Decreases Na+ Reabsorption.
•Decreases Water Reabsorption.
PTH •Increases Calcium Reabsorption.
SNS •Increases Sodium Reabsorption.

12. AldosteroneAldosterone
• Secreted by the zona
glomerulosa cells of
the adrenal cortex.
• The primary site of
aldosterone action is
on the principal cells of
the cortical collecting
tubule.

13. AldosteroneAldosterone
MechanismMechanism
• It stimulates Sodium-potassium
ATPase pump on the
basolateral side of the cortical
collecting tubule membrane.
• Aldosterone also increases the
sodium permeability of the
luminal side of the membrane.

14. Adrenal Gland DiseaseAdrenal Gland Disease
• Addison’s diseaseAddison’s disease ::
– Absence of aldosterone
– Causes marked loss of sodium (Hyponatremia)
– Causes accumulation of potassium (Hyperkalemia)
• Conn’s syndromeConn’s syndrome ::
– Excess aldosterone
– Causes Sodium retention (Hypernatremia)
– Causes Potassium depletion (Hypokalemia)

15. Angiotensin IIAngiotensin II
• It is the most powerful sodium-retaining
hormone in human body.
• It also increases Water Reabsorption.
• Produced by RAAS.
• Stimulated when a person has low arterial
pressure.

16. Angiotensin IIAngiotensin II
MechanismMechanism
1. Stimulates aldosterone.
2. Constricts efferent arterioles.
– Efferent arteriolar constriction reduces peritubular capillary hydrostatic
pressure, which increases net tubular reabsorption.
– Efferent arteriolar constriction, increases the time for plasma to stay in
glomerulus , raises filtration fraction, & increases osmotic pressure in
the peritubular capillaries; this increases the reabsorption of sodium
and water.
3. Stimulates Na+/K+ pump on basolateral membrane.
4. Stimulates Na+/H+ exchange in the luminal membrane.

17. ADHADH
• Anti Diuretic Hormone (AKA
Vasopressin).
• Produced by Hypothalamus.
• Increases the water permeability of the
distal tubule, collecting tubule, and
collecting duct.

18. ADHADH
MechanismMechanism
• ADH binds to V2 receptors in the late distal tubules,
collecting tubules, and collecting ducts, increasing the
formation of cyclic AMP and activating protein kinases.
• This, in turn, stimulates the movement of an
intracellular protein, called aquaporin-2 (AQP- 2), to
the luminal side of the cell membranes.
• The molecules of AQP-2 cluster together and fuse
with the cell membrane to form water channels that
permit rapid diffusion of water through the cells.

19. ADHADH
MechanismMechanism
• There are other aquaporins,AQP-3 and AQP-4,
in the basolateral side of the cell membrane
that provide a path for water to rapidly exit the
cells, although these are not believed to be
regulated by ADH.
• When the concentration of ADH decreases, the
molecules of AQP-2 are shuttled back to the
cell cytoplasm, thereby removing the water
channels from the luminal membrane and
reducing water permeability.

20. Atrial Natriuretic PeptideAtrial Natriuretic Peptide
• Produced by Atrium of heart
• Stimulated by “stretch in cardiac atria”
• It can be said that “ANP has opposite
function of the aldosterone”
• Decreases Sodium and Water Reabsorption.

21. Atrial Natriuretic PeptideAtrial Natriuretic Peptide
MechanismMechanism
• Increased plasma volume stretches
cardiac atria which secretes ANP.
• Increased levels of ANP,
– Inhibit the reabsorption of sodium and water
by the renal tubules,especially in the
collecting ducts.
– Increases urinary excretion.

22. Parathyroid HormoneParathyroid Hormone
• Increases Calcium Reabsorption.
• Decreases phosphate reabsorption
• Stimulation of magnesium reabsorption

23. Sympathetic Nervous SystemSympathetic Nervous System
• Activation Increases Sodium Reabsorption.
• Constricts renal arterioles, thereby reducing
GFR.
• Increases sodium reabsorption in the PCT, the
thick ascending limb of the loop of Henle, and
perhaps in more distal parts of the renal tubule.
• It also stimulates RAAS which adds to the
overall effect to increase tubular reabsorption.

24. HormonesHormones EffectEffect
Aldosterone • Increases Na+ Reabsorption
• Increases K+ Secretion
Angiotensin II •Increases Na+ Reabsorption
• Increases Water Reabsorption
ADH • Increases Water Reabsorption
ANP •Decreases Na+ Reabsorption.
•Decreases Water Reabsorption.
PTH •Increases Calcium Reabsorption.
SNS •Increases Sodium Reabsorption.

25. Renal ClearanceRenal Clearance

26. Renal ClearanceRenal Clearance
• If the plasma passing through the kidneys
contains 1 milligram of a substance in each
milliliter and if 1 milligram of this substance is
also excreted into the urine each minute.
• Then 1 ml/min of the plasma is “cleared” of the
substance.
• Which is regarded as Renal clearance.

27. Renal ClearanceRenal Clearance
• Renal clearance of a substance is the
volume of plasma that is cleared of the
substance by the kidneys per unit time.
• It is the measurement of the renal
excretion ability.

28. Renal Clearance calculationRenal Clearance calculation

29. Estimating Kidney conditionEstimating Kidney condition
Substances used for Estimating Kidney
condition
• Inulin
• Creatinine
• PAH

30. InulinInulin
• Inulin Clearance Can Be Used to Estimate GFR
(eGFR)
• Inulin is :
– Freely filtered
– Neither reabsorbed
– Nor secreted
• Whatever, inulin is filtered, all of it is excreted in
the urine.

31. InulinInulin

32. CreatinineCreatinine
• Creatinine Clearance Can Be Used to
Estimate GFR.

33. CreatinineCreatinine
• Effect of reducing
(GRF) by 50 per cent
on serum creatinine
concentration

34. CreatinineCreatinine
• It is not practical to measure urine
creatinine level to estimate GFR, so many
scientist has given many ways to calculate
GFR by being based upon only blood
creatinine.
• Widely accepted is :

35. CreatinineCreatinine
• Approximate relationship
between GFR and
plasma creatinine
concentration.
• Decreasing GFR by 50
per cent will increase
plasma creatinine to
twice normal if creatinine
production by the body
remains constant.

36. PAHPAH
• PAH Clearance Can Be Used to Estimate Renal Plasma
Flow.
• Theoretically, if a substance is completely cleared from
the plasma, the clearance rate of that substance is equal
to the total renal plasma flow.
• In other words, the amount of the substance delivered to
the kidneys in the blood (renal plasma flow X Ps) would
be equal to the amount excreted in the urine (Us X V).
Thus, renal plasma flow (RPF) could be calculated as

37. PAHPAH

38. The - EndThe - End