Buffers in the body resist changes in pH and maintain it within a narrow range. The major buffer systems are bicarbonate, phosphate, and proteins. Bicarbonate buffers work by absorbing excess hydrogen ions in the blood and tissues. The kidneys and lungs work together to control bicarbonate and carbon dioxide levels to regulate pH. When an acid is added, buffers prevent a large change in pH by neutralizing the hydrogen ions.

1. BUFFERS IN THE BODY
1
PRESENTOR : Dr.Kumar
MODERATOR
:Dr.Prabhavathy

2. 2
Buffers
 resist changes in pH from the addition of acid or
base
 in the body absorb H3O+ or OH from foods and
cellular processes to maintain pH
 are important in the proper functioning of cells
and blood
 in blood maintain a pH close to 7.4; a change in
the pH of the blood affects the uptake of oxygen
and cellular processes

3. Buffers (continued)
When an acid or
base
is added
 to water, the pH
changes drastically
 to a buffer solution,
the pH does not
change very much;
pH is maintained
3

4. Components of a Buffer
4
The components of a buffer solution
 are acid–base conjugate pairs
 can be a weak acid and a salt of its conjugate
base
 typically have equal concentrations of the
weak acid and its salt
 can also be a weak base and a salt of its
conjugate acid

5. The Major Body Buffer Systems

6. Body Buffer system

7. -Hydrogen ion Homeostasis
-Control system
-Control CO2 (PCO2)
By lungs
-Control HCO3- By
Kidney and Erythrocytes

8. Body Buffer system
• Hydrogen Ion Homeostasis
About 50 to100 m mol of hydrogen ions are
released from cells into extracellular fluid each
day
• Hydrogen ion concentration [H+] is
maintained between about 35 and 45 nano
molL. (40nmol/L=pH 7.4)
• Control of hydrogen ion balance depends
on the secretion of H+ from the body, mainly
into the urine therefore Renal impairment
causes acidosis

9. -Aerobic metabolism of the carbon skeletons of
organic compounds converts from hydrogen,
carbon and oxygen to water and carbon dioxide
(CO2)
9
C C C C C C
H H H H H H
HHHHHH

10. CO2 is essential compound of extracellular buffering
system
-Control of CO2 depends on normal lung function.

11. Buffering
Is a process by which a strong acid (or base) is
replaced by a weaker one, with a consequent
reduction in the number of free hydrogen ions and
therefore the change in PH
HCl + NaHCO3 = H2CO3 + NaCl
Strong acid buffer weak acid neutral salt

12. PH is a measure of hydrogen ion
activity
Log 100 =log 102=2
Log 107=7
If [H+] is 10-7 (0.000 0001)
Then log [H+] =-7
The Henderson –hasselbalch equation
PH=PK+log [base] /[acid]

13.  The bicarbonate pair is an important biological
buffer example;
H2CO3 HCO3
- + H+
Acid base
 The base is bicarbonate (HCO3
-) and the carbonic
acid (H2CO3) .
 -It is not possible to measure the latter directly
 however it is in equilibrium with dissolved CO2 of
which the partial pressure (PCO2) can be estimated.

14. The conc. of H2CO3 is derived by multiplying this
measured value by the solubility co efficient (s) for
CO2 therefore
PH =PK-log [HCO3
-]/PCO2 XS (0.03 )

15. Hydrogen ion Homeostasis
PH is relatively tightly controlled in blood by the
following mechanisms
1-Hydrogen ions can be incorporated in water
H+ + HCO3
- H2CO3 CO2 + H2O

16.  This is normal mechanism during oxidative phos
phorylation. H+ is inactivated by combining with
the HCO3 only if the reaction is driven to the
right by the removal of CO2.
 By this would cause bicarbonate depletion
 H+ can be lost from the body only through the
kidney and the intestine .This mechanism is
coupled with the generation of bicarbonate ion
(HCO3
-)
 In the kidney this is the method which secretion
of excess H+ ensures regeneration of buffering
capacity

17. Control system
 CO2 and H+ are potentially toxic products of
aerobic and anaerobic metabolism
 most CO2 is lost through the lungs but some is
converted to bicarbonate
 Thus contributing important extracellular buffering
capacity
 Bicarbonate system is the most important buffer
in the body because has high capacity.

18. The control of CO2 (PCO2) by the
Respiratory center and lungs
The partial pressure of CO2 in plasma is normally
about 5.3 kpa (40 mmHg) and depend on the
balance between the rate of production by
metabolism and the loss through the pulmonary .

19.  the rate of respiration, and then therefore the rate of
CO2 elemination is controlled by chemoreceptor in
the respiratory centre in the medulla of the brain.
 The receptors respond to changes in the [CO2]or[H+]
of plasma or of the cerebrospinal fluid .
1. the PCO2 rises much above 40 mm of Hg
2. the PH falls, the rate of respiration increases .

20.  Normal lungs have a very large reserve capacity for CO2
elimination
 The normal respiratory centre and lungs can control CO2
conc. Within norrow limits by responding to changes in
the [H+] and therefore compensate for changes in acid-
base disturbances .
 diseases of the lungs, or abnormalities of respiratory
control, primarily affect the PCO2

21. The Control of Bicarbonate by
-The Kidneys and Erythrocytes
The renal tubular cells and erythrocytes
generate bicarbonate, the buffer base in the
bicarbonate system from CO2 under physiological
conditions.

22.  The erythrocyte mechanism makes fine adjustments
to the plasma bicarbonate conc. In response to
changes in PCO2 in lungs and tissues.
 The kidneys play the major role in maintaining the
circulating bicarbonate conc. And in elimination H+
from the body.

23. The carbonate dehydratase
system
 Bicarbonate is produced following the dissociation
of carbonic acid formed from CO2and H2O.
 This is catalyzed by carbonate dehydratase (CD)
present in high conc. in erythrocytes and renal
tubular cells.
CO2 + H2O H2CO3 H+ + HCO3
-
Carbonate
dehydratas
e

24.  In addition to content erythrocytes and
renal tubular cell to CD they also have means of
removing one of the products, H+ thus both
reactions continues to the right and HCO3- is
formed.
 one of the reactants, water, is freely available and
one of the products, H+ is removed.

25.  HCO3
- generation is therefore accelerated if the
conc.of
1. CO2 rises
2. HCO3
- falls.
3. H+ falls because it is either buffered by
erythrocytes or excreted from the body by
renal tubular cells.
 Therefore an increase of intracellular P CO2 or
decrease in intracellular [HCO3
-] in the
erythrocytes and renal tubular cells maintain the
extracellular bicarbonate conc. by accelerating
the production of HCO3
-.
 This minimizes changes in the ratio of [HCO3
-] to

26. In normal subject, at a plasma ;
1. PCO2 of 40mm of hg (a CO2 of about 1.2
mmolL)
2. Erythrocytes and renal tubular cells keep the
extracellular bicarbonate at about 25 mmolL
3. The extracellular ratio of [HCO3
-] to [CO2] (both
in mmolL) is just over 20:1.

27. Bicarbonate Generation by the
Erythrocytes
 Erythrocytes produce little CO2 as they lack aerobic
pathway
 Plasma CO2 diffuses along a concentration gradient
into erythrocytes, where carbonate dehydratase
catalyses its reaction with water to from carbonic
acid (H2CO3) which then dissociates
 Much of the H+ is buffered by hemoglobin and the

28. DIOXIDE
DIFFUSION
28 CO2
Red Blood Cell
Systemic Circulation
H2O
H+ HCO3
-
carbonic
anhydrase
Plasma
CO2 CO2
CO2 CO2 CO2 CO2
CO2
Click for Carbon
Dioxide diffusion
+ +
Tissues
H+
Cl-
Hb
H+ is buffered by
Hemoglobin

29. The kidneys
Two renal mechanism control [HCO3
-]in the
extracellular fluid:
Bicarbonate reclamation (reabsorption)
 The CO2 driving in renal tubular cells is derived
from filtered bicarbonate, after action of the
carbonate dehydratase.
 There is no correct to an acidosis but can
maintain a steady state.

30.  Normal urine is nearly HCO3
- free. An amount
equivalent to that filtered by the glomeruli is
returned to the body by the tubular cells.
 The luminal surface of renal tubular cells are
impermeable to HCO3
- .
 Thus, HCO3
- can only be returned to the body if
first converted to CO2 in the tubular Lumina, and
an equivalent amount of CO2 is converted to
HCO3
- with in tubular cells.

31.  The luminal surface of renal tubular cells are
impermeable to HCO3
- , Thus, HCO3
- can only be
returned to the body if first converted to CO2 in the
tubular Lumina, and an equivalent amount of CO2
is converted to HCO3
- with in tubular cells.

32. 32
Capillary Distal Tubule Cells
Tubular Urine
NH3
Na+ Cl-+
H2CO3HCO3
- +
NaCl
NaHCO3
Click Mouse to
Start Animation
NaHCO3
NH3Cl-
H+
NH4Cl
Click Mouse to See
Animation Again
Notice the
H+ - Na+
exchange to
maintain
electrical
neutrality

33. Bicarbonate generation
 A very important mechanism for correcting acidosis,
in which the levels of CO2 or [HCO3
-] affecting the
carbonate dehydratase reaction in tubular cells
reflect those in the extracellular fluid, there is a net
loss of H+

34. PHOSPHATE BUFFER SYSTEM
34
 1) Phosphate buffer system
Na2HPO4 + H+ NaH2PO4 + Na+
Most important in the intracellular system
Alternately switches Na+ with H+
H+ Na2HPO4+
NaH2PO4Click to
animate
Na++

35. PHOSPHATE BUFFER SYSTEM
35
Na2HPO4 + H+ NaH2PO4 + Na+
 Phosphates are more abundant within the
cell and are rivaled as a buffer in the ICF by
even more abundant protein
Na2HPO4
Na2HPO4
Na2HPO4

36. PHOSPHATE BUFFER SYSTEM
36
 Regulates pH within the cells and the urine
Phosphate concentrations are higher
intracellularly and within the kidney tubules
Too low of a
concentration in
extracellular fluid
to have much
importance as an
ECF buffer system HPO4
-2

37. PROTEIN BUFFER SYSTEM
37
 Behaves as a buffer in both plasma and cells
 Hemoglobin is by far the most important
protein buffer.
 Most important intracellular buffer (ICF)
 The most plentiful buffer of the body
 Proteins are excellent buffers because they contain
both acid and base groups that can give up or take up
H+
 Proteins are extremely abundant in the cell
 The more limited number of proteins in the plasma
reinforce the bicarbonate system in the ECF

38. 38
 Hemoglobin buffers H+ from metabolically
produced CO2 in the plasma only
 As hemoglobin releases O2 it gains a great
affinity for H+
Hb
O2
O2 O2
O2
H+

39. 39
 H+ generated at the tissue level from the
dissociation of H2CO3 produced by the
addition of CO2
 Bound H+ to Hb (Hemoglobin) does not
contribute to the acidity of blood
Hb
O2
O2 O2
O2

40. 40
 As H+Hb picks up O2 from the lungs the Hb
which has a higher affinity for O2 releases H+
and picks up O2
 Liberated H+ from H2O combines with HCO3
-
HCO3
- H2CO3 CO2 (exhaled)
Hb
O2
O2 O2
H+

41. 41
 Venous blood is only slightly more acidic than
arterial blood because of the tremendous
buffering capacity of Hb
 Even in spite of the large volume of H+
generating CO2 carried in venous blood

42. 42
 Proteins can act as a buffer for both acids and
bases
 Protein buffer system works instantaneously
making it the most powerful in the body
 75% of the body’s buffer capacity is controlled
by protein
 Bicarbonate and phosphate buffer systems
require several hours to be effective

43. PROTEIN BUFFER SYSTEM
43
 Proteins are very large, complex molecules
in comparison to the size and complexities of
acids or bases
 Proteins are surrounded by a multitude of
negative charges on the outside and
numerous positive charges in the crevices of
the molecule
-
-
-
- - - -
-
-
-
-
-
-
--------
-
---
-
-
-
-
- - - -
+
+
++
+
+
+
+
+
+
+
+
+
++ +
+
+
+
+
+
+
+ +
+

44. PROTEIN BUFFER SYSTEM
44
 H+ ions are attracted to and held from
chemical interaction by the negative charges
-
-
-
- - - -
-
-
-
-
-
-
--------
-
---
-
-
-
-
- - - -
+
+
++
+
+
+
+
+
+
+
+
+
++ +
+
+
+
+
+
+
+ +
+
H+
H+
H+
H+ H+ H+ H+ H+ H+ H+
H+
H+
H+
H+
H+H+H+H+H+H+H+

45. PROTEIN BUFFER SYSTEM
45
 OH- ions which are the basis of alkalosis are
attracted by the positive charges in the
crevices of the protein
-
-
-
- - - -
-
-
-
-
-
-
--------
-
---
-
-
-
-
- - - -
+
+
++
+
+
+
+
+
+
+
+
+
++ +
+
+
+
+
+
+
+ +
+
OH-
OH-
OH-
OH-
OH-
OH-
OH-
OH-
OH-OH-
OH-
OH-

46. PROTEIN BUFFER SYSTEM
46
-
-
-
- - - -
-
-
-
-
-
-
--------
-
---
-
-
-
-
- - - -
+
+
++
+
+
+
+
+
+
+
+
+
++ +
+
+
+
+
+
+
+ +
+
OH-
OH-
OH-
OH-
OH-
OH-
OH-
OH-
OH-OH-
OH-
OH-
H+
H+
H+
H+ H+ H+ H+ H+ H+ H+
H+
H+
H+
H+
H+H+H+H+H+H+H+