The body maintains tight regulation of arterial blood pH between 7.35-7.45 through acid-base balance mechanisms. It uses buffer systems, and respiratory and renal systems to neutralize acids and bases. The major buffer systems are bicarbonate, phosphate, and proteins, which maintain pH by donating or accepting hydrogen ions. Deviations outside the normal pH range can impair membrane and protein function and are not survivable. The lungs and kidneys work to restore pH through removing carbon dioxide and hydrogen ions respectively.

1. Acid Base balanceAcid Base balance
Acid-base balance refers to the mechanisms the bodyAcid-base balance refers to the mechanisms the body
uses to keep its fluids close to neutral pH (that is,uses to keep its fluids close to neutral pH (that is,
neither basic nor acidic) so that the body can functionneither basic nor acidic) so that the body can function
normally.normally.
Arterial blood pH is normally closely regulated toArterial blood pH is normally closely regulated to
between 7.35 and 7.45.between 7.35 and 7.45.

2. acidsacids ？？
basesbases ？？
Any ionic or molecular substanceAny ionic or molecular substance
that can act as a proton donor.that can act as a proton donor.
Strong acidStrong acid ：： HCl, HHCl, H22SOSO44, H, H33POPO44..
Weak acidWeak acid ：： HH22COCO33, CH, CH33COOH.COOH.
Any ionic or molecular substanceAny ionic or molecular substance
that can act as a proton acceptor.that can act as a proton acceptor.
Strong alkaliStrong alkali ：： NaOH, KOH.NaOH, KOH.
Weak alkaliWeak alkali ：： NaHCONaHCO33, NH, NH33,,
CHCH33COONa.COONa.

3. pH
• pH is the negative log of hydrogen ion
concentration.
pH= -log[H+]
 If [H+
] is high, the solution
is acidic; pH < 7
 If [H+
] is low, the solution
is basic or alkaline ; pH > 7

4. pH of ECF is between 7.35 and 7.45pH of ECF is between 7.35 and 7.45.. Deviations, outsideDeviations, outside
this range affect membrane function, alter proteinthis range affect membrane function, alter protein
function, etc.function, etc.
- You cannot survive with a pH <6.8 or >7.7- You cannot survive with a pH <6.8 or >7.7
- Acidosis- below 7.35Acidosis- below 7.35
Alkalosis- above 7.45Alkalosis- above 7.45

5.  In normal individuals, pH is controlled by
two major and related processes
pH regulation and pH compensation.
 Regulation is a function of the buffer
systems of the body in combination with
the respiratory and renal systems,
 Compensation requires further
intervention of the respiratory and/or renal
systems to restore normalcy.

6. Maintenance of Acid-Base balance
• Acid base balance is regulated by three
main process,
• Buffer systems.
• Respiratory system.
• Renal function.

7. • Respiratory System:
• Removal of CO2
by lungs – stabilizes the
ECF, has direct effect on Carbonic Acid –
Bicarbonate Buffer System
• Renal System:
• Removal of H+
ions by kidneys
• Regulation By Buffers

8. Regulated by buffer system:
• BUFFER:
• Ability of an acid-base mixture to resist sudden
changes in pH is called its buffer.
• Three major chemical buffer systems in the body
are:
• Carbonic acid-bicarbonate buffer system
• Phosphate buffer system
• Protein buffer system

9. Buffer Systems in Body Fluids
Figure 27.7

10. 1) The Bicarbonate (HCO3
-
) Buffer
System
 The bicarbonate buffer system is an
important buffer system in the acid base homeostatis of
living organisms. As a buffer, it tends to maintain a
relatively constant plasma.
 Prevents changes in pH caused by organic acids and
fixed acids in ECF
 The CO2 is removed by the lungs.

11. The Bicarbonate (HCO3
-
) Buffer System (contd)
• Carbonic acid (H2CO3) is a weak acid and is therefore in
equilibrium with bicarbonate (HCO3
-
) in solution. When
significant amounts of both carbonic acid and
bicarbonate are present, a buffer is formed. This buffer
system can be written as:
CO2+H2O------>H2CO3------> HCO3+H
• Under normal circumstances there is much more
bicarbonate present than carbonic acid (the ratio is
approximately 20:1). As normal metabolism produces
more acids than bases, this is consistent with the body's
needs.

12. • The blood, with its high base concentration, is able to
neutralize the metabolic acids produced. Since relatively
small amounts of metabolic bases are produced, the
carbonic acid concentration in the blood can be lower.
• The optimal pH is the pKa for the acid in the system. In
this case the acid is carbonic acid.
• Ka=4.3 x 10-7
, pKa=6.4

13. • Bicarbonate buffer system
• H2CO3 -----> H+ + HCO3
-
• When pH is rising:
H2CO3 + H+ ---> HCO3
-
• When pH is falling:
H2CO3 H+ <---- HCO3
-
.

14. ADVANTAGES & DISADVANTAGE
• ADVANTAGE
• Bicarbonate buffer system is quite efficient as compared
to other buffer system since it is present in very high
concentration & it produce H2CO3 from which CO2 is
exhaled out.
• DISADVANTAGE:
• Bicarbonate is very weak buffer & hence pKa is very far
away from physiological pH.
• Cannot protect the ECF from pH changes
due to increased or depressed CO2 levels.

15. 2) The Phosphate Buffer System
• The phosphate buffer system (HPO4
2-
/H2PO4
-
) plays a role
in plasma and erythrocytes.
• H2PO4
-
+ H2O ↔ H3O+
+ HPO4
2-
• Any acid reacts with monohydrogen phosphate to form
dihydrogen phosphate
dihydrogen phosphate monohydrogen phosphate
H2PO4
-
+ H2O ← HPO4
2-
+ H3O+
• The base is neutralized by dihydrogen phosphate
dihydrogen phosphate monohydrogen phosphate
• H2PO4
-
+ OH-
→ HPO4
2-
+ H3O+

16. • Their action is nearly identical to bicarbonate buffer
• Mainly sodium salts of ;
• Dihydrogen phosphate (H2PO4) a weak acid
• Monohydrogen phosphate (HPO4) ,a weak base
• The normal ratio in plasma is 4:1 and this is kept
constant by the help of kidneys for which phosphate
buffer system is directly related to the kidneys.

17. . This dihydrogen phosphate is an efficient
buffer in intracellular metabolism.
• Phosphate buffer system:
• H2PO4
-
----> H+
+ HPO4
–
• When pH is rising: H2PO4
----->
H+
+ HPO4
--
;
• When pH is falling: H2PO4<------H+
+ HPO4

18. ADVANTAGE & DISADVANTAGE
 The phosphate buffer system has a pK of 6.8, which is
not far from the normal pH of 7.4 in the body fluids; this
allows the system to operate near its maximum buffering
power.
Ka=6.2 x 10-8
, pKa=7.2
DISADVANTAGE
 Provide only temporary solution to acid–base imbalance
 Do not eliminate H+
ions

19. 3) The Protein Buffer System
• The protein buffer system is part of body mechanism for
controlling blood H+ ion concentration both ECF & ICF
 More concentrated than either bicarbonate or phosphate
buffers
 Accounts for about three-quarters of all chemical
buffering ability of the body fluids,

20. AMINO ACIDS;
 The carboxyl groups release H+
when pH rises and
amino groups bind H+
when pH falls.
 In acidic media protein act as base , NH2 group takes up
H+ and formed NH3. Here, protein become positively
charged.
• In alkaline media , protein act as acid and acidic group
(COOH) dissociate in to COO- & H+. In this case protein
become negatively charged.
NH2-CH2-CH2… CH2-CH2-COOH
H+ H+

21. Protein Buffers
• Carboxyl group gives up H+.
• Amino Group accepts H+.

22. Protein Buffers
• Proteins contain – COO-
groups, which, like acetate ions
(CH3COO-
) can act as proton donors.
• Proteins also contain – NH3
+
groups, which, like
ammonium ions (NH4
+
), can accept protons.
• If acid comes into blood, hydronium ions can be
neutralized by the – COO-
groups
• - COO-
+ H3O+
→ - COOH + H2O
• If base is added, it can be neutralized by the – NH3
+
groups
• - NH3
+
+ OH-
→ - NH2 + H2O

23. Hemoglobin & Plasma protein
• Protein buffers in blood include haemoglobin
(150g/l) and plasma proteins (70g/l).
• Haemoglobin is quantitatively about 6 times
more important then the plasma proteins as it is
present in about twice the concentration and
contains about three times the number of
histidine residues per molecule.
• Hemoglobin buffer system H+
are buffered by
hemoglobin

24. Acid-Base Imbalances
• pH< 7.35 acidosis
• pH > 7.45 alkalosis
• The body response to acid-base
imbalance is called compensation

26. THANK YOU