Physio Renal 6.

Medical college lectures: Ranal physiology 2nd year.

1. Acid – Base Balance.
Dr.Mohamad Shaikhani.Dr.Mohamad Shaikhani.

2. none of the most important renal functions, one of the most important renal functions,
regulating the acid – base balance of the body to regulating the acid – base balance of the body to
ensure neutral PH of the body (not acidic & not ensure neutral PH of the body (not acidic & not
alkaline) by regulating the hydrogen ion & alkaline) by regulating the hydrogen ion &
bicarbonate concen of the body, bicarbonate concen of the body,
nBlood 7.4,interstitium 7.35, intracellular 7 at which Blood 7.4,interstitium 7.35, intracellular 7 at which
level the metabolic functions of the body are level the metabolic functions of the body are
operating optimally.operating optimally.
nNormal Hydrogen ion concentration of the body Normal Hydrogen ion concentration of the body
(H+) = 10(-8) – 1.6 *10(-7) MEQ/L.(H+) = 10(-8) – 1.6 *10(-7) MEQ/L.
nPH = -LogH+ = 7.4.PH = -LogH+ = 7.4.
nIncreased PH= low H+ = Alkalosis. Increased PH= low H+ = Alkalosis.
Decreased PH =High H+ = Acidosis.Decreased PH =High H+ = Acidosis.
nAcid is a proton H+ Donor. Acid is a proton H+ Donor.
Alkaline is H+ Acceptor.Alkaline is H+ Acceptor.
nHcl is strong acid ,H2CO3 Weak acid , NaOH Hcl is strong acid ,H2CO3 Weak acid , NaOH
strong base & Na2HPO4 Weak base.strong base & Na2HPO4 Weak base.

3. Buffer systems of the Body:
nAre defense of the body against changes in the H+ ion Are defense of the body against changes in the H+ ion
concentration of the body. Their functions is to prevent concentration of the body. Their functions is to prevent
marked changes(increase or decrease) in the body PH when a marked changes(increase or decrease) in the body PH when a
strong base or strong acid is added to the circulation ,by strong base or strong acid is added to the circulation ,by
forming much weaker acid or base.forming much weaker acid or base.
nThey are of 3 types:They are of 3 types:
n1.Acid – base Buffer systems:1.Acid – base Buffer systems:
A. Bicarbonate buffer system A. Bicarbonate buffer system
B. Phosphate buffer system.B. Phosphate buffer system.
C. Protein buffer system.C. Protein buffer system.
n2. Respiratory regulation.2. Respiratory regulation.Acts within 1 – 12 minutes in acute Acts within 1 – 12 minutes in acute
situations & within 1 day in chronic situations.situations & within 1 day in chronic situations.
n3.Renal regulation:3.Renal regulation:The most powerful buffering system, it The most powerful buffering system, it
requires many hours to several days to act maximally.requires many hours to several days to act maximally.
PH = - Log H+ ……………………..(1).PH = - Log H+ ……………………..(1).

4. 1.Acid – base Buffer systems:
nIs a mixture of a weak acid & a weak base( carbonic acid H2CO3 – Is a mixture of a weak acid & a weak base( carbonic acid H2CO3 –
bicarbonate NaHCO3 mixture), it prevents marked change in the PH of the bicarbonate NaHCO3 mixture), it prevents marked change in the PH of the
body when strong acid or strong base is added to the circulation by forming body when strong acid or strong base is added to the circulation by forming
much weaker acid or base as:much weaker acid or base as:
HCL (Strong Acid) + NaHCO3 = H2CO3(Weaker acid) + Nacl ….(2).HCL (Strong Acid) + NaHCO3 = H2CO3(Weaker acid) + Nacl ….(2).
NaOH(Strong base) + H2CO3 = NaHCO3( Weaker base) +H2O…(3).NaOH(Strong base) + H2CO3 = NaHCO3( Weaker base) +H2O…(3).
H2CO3 = H + + HCO3- ………………………………………...(4).H2CO3 = H + + HCO3- ………………………………………...(4).
H+*HCO3-/H2CO3 = K …………………………………….….(5).H+*HCO3-/H2CO3 = K …………………………………….….(5).
H+*HCO3/CO2 = K …………………………………………(6).H+*HCO3/CO2 = K …………………………………………(6).
K = 1/400 K- K = 1/400 K-
H+ = K*CO2/HCO3 …………………………………………(7).H+ = K*CO2/HCO3 …………………………………………(7).
Log H+ = Log K + LogCO2/HCO3 ………………………………(8).Log H+ = Log K + LogCO2/HCO3 ………………………………(8).
-Log H+ = - Log K + LogHCO3/CO2 ………………………….(9).-Log H+ = - Log K + LogHCO3/CO2 ………………………….(9).
PH = PK + LogHCO3/CO2 …………………………………...(10).PH = PK + LogHCO3/CO2 …………………………………...(10).
PH of the solution = PH of the buffer +pHCO3/CO2…………(11).PH of the solution = PH of the buffer +pHCO3/CO2…………(11).
nPH = 6.1 +LogHCO3/CO2………..(12).PH = 6.1 +LogHCO3/CO2………..(12).
nEquation 12 is called Henderson – Hasselbach equation.Equation 12 is called Henderson – Hasselbach equation.
nPH = 6.1 + Log 1 (if HCO3 = CO2).PH = 6.1 + Log 1 (if HCO3 = CO2).
nPH = 6.1 + ZERO = 6.1PH = 6.1 + ZERO = 6.1
nHCO3 Changed by renal system & CO2 by respiratory system.HCO3 Changed by renal system & CO2 by respiratory system.

5. The Buffering power of the Bicarbonate
buffer system depends on:
n1.The ratio of bicarbonate to carbonic acid:1.The ratio of bicarbonate to carbonic acid:
It is greatest when the ratio is 1 i.e PH = PK ,But it is still active It is greatest when the ratio is 1 i.e PH = PK ,But it is still active
when the ratio is 8/1 or 1/8.when the ratio is 8/1 or 1/8.
n2.Contribution of the renal & respiratory systems:2.Contribution of the renal & respiratory systems:
Normally the ratio of NaHCO3/H2CO3 = 20/1 with blood PH of Normally the ratio of NaHCO3/H2CO3 = 20/1 with blood PH of
7.4 & PK of 6.1 ,so it is not maximally active ,but the 7.4 & PK of 6.1 ,so it is not maximally active ,but the
contribution of renal system by regeneration & retention of contribution of renal system by regeneration & retention of
NaHCO3 & the respiratory system by regulating NaHCO3 & the respiratory system by regulating
CO2(H2CO3) in blood makes this bicarbonate –carbonic acid CO2(H2CO3) in blood makes this bicarbonate –carbonic acid
buffer system a very powerful buffer system.buffer system a very powerful buffer system.

6. B. Phosphate buffer system.
nIs a mixture of Na2HPO4 & NaH2PO4 Is a mixture of Na2HPO4 & NaH2PO4
nHCL +Na2HPO4 = NaH2PO4 + NaCL ……………(13).HCL +Na2HPO4 = NaH2PO4 + NaCL ……………(13).
nNaOH + NaHPO4 = Na2HPO4 + H2O …………..(14).NaOH + NaHPO4 = Na2HPO4 + H2O …………..(14).
nThe PK of this buffer system is 6.8 very near the 7.4 (normal The PK of this buffer system is 6.8 very near the 7.4 (normal
blood PH) , so it is very effective buffer system, even more blood PH) , so it is very effective buffer system, even more
effective than bicarbonate BS ,But its concentration in the blood effective than bicarbonate BS ,But its concentration in the blood
is 1/12 of the bicarbonate BS concentration ,so as end result is is 1/12 of the bicarbonate BS concentration ,so as end result is
less effective than Bicarbonate BS ,less effective than Bicarbonate BS ,
nBut it is more effective buffering system in the renal tubules & But it is more effective buffering system in the renal tubules &
inside cells of the body for buffering the H+ ion secreted by the inside cells of the body for buffering the H+ ion secreted by the
kidneys & inside cells ,as its concentration in the renal tubules & kidneys & inside cells ,as its concentration in the renal tubules &
cells is high.cells is high.

7. C.Protein Buffer system:
nIs important in buffering inside cells as the Is important in buffering inside cells as the
concentration of protein inside cells is high. The concentration of protein inside cells is high. The
proteins are dissociated into amino acids which are proteins are dissociated into amino acids which are
acidic radicals giving H+ . acidic radicals giving H+ .
nBicarbonate BS diffuse slowly to inside cells ,so the Bicarbonate BS diffuse slowly to inside cells ,so the
protein BS inside cells corrects any acid – base protein BS inside cells corrects any acid – base
abnormalities until the Bicarbonate BS arrives & abnormalities until the Bicarbonate BS arrives &
corrects the final abnormalities after several hours.corrects the final abnormalities after several hours.

8. 2.Respiratory regulation of Acid – Base balance:
nRespiratory buffering power is ½ of all other Respiratory buffering power is ½ of all other
buffering systems. Alveolar ventilation causes buffering systems. Alveolar ventilation causes
reciprocal changes in the H+ ion concentration of the reciprocal changes in the H+ ion concentration of the
blood as H+ in the blood affects the respiratory blood as H+ in the blood affects the respiratory
center causing increase or decrease in the alveolar center causing increase or decrease in the alveolar
ventilation.ventilation.
CO2 = 1/Alveolar ventilation .CO2 = 1/Alveolar ventilation .
Alveolar ventilation can increase 15 times.Alveolar ventilation can increase 15 times.

9. Feed back control of H ion concentration of the blood by Feed back control of H ion concentration of the blood by
respiratory center:respiratory center:
nThe efficiency of respiratory system buffering power is The efficiency of respiratory system buffering power is
50 – 75% ,when the acid – base abnormality is outside 50 – 75% ,when the acid – base abnormality is outside
the respiratory system ,when PH shifts from normal of the respiratory system ,when PH shifts from normal of
7.4 to 7 or to 7.8 ,the respiratory system works in 1- 12 7.4 to 7 or to 7.8 ,the respiratory system works in 1- 12
minutes returning the PH to 7.2 – 7.3 ,but not to normal minutes returning the PH to 7.2 – 7.3 ,but not to normal
i.e 50 – 75% efficient.i.e 50 – 75% efficient.

10. .In Acidosis kidneys secrete excess H+ in urine , while in .In Acidosis kidneys secrete excess H+ in urine , while in
Alkalosis kidneys regenerate & reabsorb bicarbonate.Alkalosis kidneys regenerate & reabsorb bicarbonate.
.Renal Hydrogen H+ ion & bicarbonate secretion is .Renal Hydrogen H+ ion & bicarbonate secretion is
directly related to H+ & Bicarbonate concentration in directly related to H+ & Bicarbonate concentration in
blood & ECF i.e in acidosis there will be more H+ blood & ECF i.e in acidosis there will be more H+
secretion than Bicarbonate & vice versa in Alkalosis.secretion than Bicarbonate & vice versa in Alkalosis.
.Normally slightly more acid is secreted than bicarbonate.Normally slightly more acid is secreted than bicarbonate
.Kidneys are more powerful buffering system but they are .Kidneys are more powerful buffering system but they are
slow as chemical buffers act within seconds, respiratory slow as chemical buffers act within seconds, respiratory
system within minutes & kidneys within hours to days.system within minutes & kidneys within hours to days.
3.Renal control of H+ ion concentration & acid – base
balance:

11. Renal tubular secretion of H+ ion:
Proximal tubules. Distal tubule.
1.Occure in proximal tubule
segments.

2.Contributes to 95% of H+
secreted by kidneys.
3.Concentrates H+ *4.
4.It is secondary active secretion.
5.It occurs in all proximal
tubular cells.

1.Occure in distal tubule
segments & pelvis.

2.Contributes to 5% of H+
secreted by kidneys.
3.Concentrates H+ *900.
4.It is primary active secretion.
5.It occurs in only intercalated or
dark cells.

12. Renal tubTransport of Excess H+ ion in
the urine with urinary buffers:
.Urinary PH is 6(4.8 – 8),only 1% of H ion secreted in
urine is free while 99% is secreted with the urinary
buffering systems which include:
1.Amonia BS.
2.Phosphate BS.

13. 1.Amonia BS in the renal tubules:
Amonia is formed from Gultamin by the enzyme
glutaminase in the tubular cells ,the formed
ammonia diffuses into the lumen to bind the excess
H+ secreted into the tubular lumen to form NH4
which binds with CL coming from NaCL to form
NH4CL.

14. 2.Phosphate BS in the renal tubules:
It is an effective buffer system in the renal tubules as
its concentration there is high &its PK 6.8 near to the
normal blood PH of 7.4.

15. Causes of Acid – Base abnormalities:
Acidosis. Alkalosis.
Respiratory Metabolic Respiratory Metabolic
1.Hypoventilati
on causing
CO2
accumulation.
2.Respiratory
center damage.
3.Respiratory
obstruction.
4.Pneumonia.
1.Diabetes
Mellitus.
2.Renal failure.
3.Acid
ingestion.
4.Alcoholic
ketoacidosis.
5.Lactic
acidosis.
1.Hyperventilat
ion causing
CO2 wash as in
hysteria or
high altitude.
1.Diuretics.
2.Alkali
ingestion.
3.Pyeloric
obstruction.
4.Hyperaldoste
ronism.

16. Clinical features:
Acidosis:
CNS depression leading to drowsiness ,confusion & coma with
deep sighing respiration called kausmal’s breath.
Alkalosis:
On the other hand causes hyper excitability of the CNS
causing tetany ,carpopedal spasm ,numbness & convulsions.
Treatment:
Acidosis: Sodium Bicarbonate or lactate or gluconate IV
slowly.
Alkalosis: Oral NH4CL or lysine monoHCL.
PH measurements;By Glass electrode PH meter of plasma
with special care during pl