This document discusses acid-base balance and buffers. It defines pH and describes strong and weak acids and bases. The key physiological buffers - bicarbonate, phosphate, hemoglobin and proteins/amino acids - are explained in terms of how they maintain blood pH during the addition of acids or bases. The document also covers acid-base imbalance disorders like acidosis and alkalosis, their causes and compensation mechanisms. Arterial blood gases are described as a way to diagnose acid-base disorders. An example case of metabolic acidosis in an infant with diarrhea is analyzed.

1. Buffersand Buffering
Dr. Ayat samy
Assistant lecturer of biochemistry, faculty of
veterinary medicine, Suez canal university

2. 2
 Concepts of pH , buffers
 Mechanism of buffering
 Physiological buffers
 Acid – Base Balance
 Acid – Base Imbalance
 Acid – Base Imbalance Cases
Contents of section

3. 3
 pH is a method of expressing the acidity or basicity of solution.
 pH is a measure of the concentration of hydrogen ions in a solution.
 pH is – log {H+}
Concept of pH

4. 4
Classification of substances acc. to pH
Acid Base
Amphoteric

5. 5
Acid
 Substance that give {H+} ions in solution or that donate proton.
Acids
Strong
acid
Weak
acid

6. 6
Strong acid
 It is an acid that virtually 100% ionized (completely release all of its hydrogen ) in
water.

7. 7
Examples
Strong acid
 Hydrochloric acid (HCl)
 Nitric acid (HNO3)
 Sulfuric acid (H2SO4)

8. 8
Weak acid
 It is an acid which doesn't ionize fully (does not completely release all of its
hydrogens) when dissolved in water.

9. 9
Examples
Weak acid
 Acetic acid (CH3COOH)
 Carbonic acid (H2CO3)

10. 10
Types of acidity
It is the concentration of
{H+} ions in a solution
or
Is the pH of the solution.
It is the concentration of {H+}
ions in a solution
+
{H+} available for ionization
although not ionized at the time.
 True acidity  Titratable acidity
(Total acidity)

11. 11
Base
 Substance that give {OH-} ions in solution or accept proton.
Bases
Strong
base
Weak
base

12. 12
Strong base
 It is a base that virtually 100% ionized (completely release all of its hydroxide
ions) in water.

13. 13
Examples
Strong base
 Sodium hydroxide (NaOH)
 Potassium hydroxide (KOH)

14. 14
Weak base
 It is a base that partially ionized (does not completely release all of its hydroxyl
group) in water.

15. 15
Examples
Weak base
 Ammonia (NH3)

16. 16
Amphoteric substance
Examples
 Substance that act as acids and bases.
 H2O
 Amino acids

17. 17
Importance of pH in our bodies

18. 18
Blood pH : 7.35 - 7.45 (any change is fetal)
Urine pH : 6.8 (slightly acidic)
Gastric juice pH : 1-2 (highly acidic)
Any change in pH leads to precipitate some types of salts
present normally in soluble form and urinary stones.
Increase of acidity leads to peptic ulcer
Decrease of acidity lead to hypoacidity.
Importance of pH in some body fluid in
our bodies

19. 19
Importance of pH in some body fluid in
our bodies
Semen pH : 7.2 – 8 (alkaline)
Any change leads to sterility
The activity of most chemical reactions occurs inside the body
is dependent on fluid pH.

20. 20
Buffers and Buffering

21. 21
Buffers
Are solutions which can resist sudden or large change in the pH when strong acid
or base are added .

22. 22
Composition of buffer:
solutions of weak acids and their conjugate bases.
solution of weak bases and their conjugate acids.
Buffers

23. 23
Composition of buffer:
solutions of weak acids and their conjugate bases.
solution of weak bases and their conjugate acids.
Buffers
In acid-base reactions, the acid is converted into its conjugate base and the
base is converted into its conjugate acid.

24. 24
Buffer pairs
The best buffer pairs are:
 Weak acids and salts of these weak acids with strong bases
 Weak bases and salts of these weak bases with strong acid

25. 25
Examples of bufferpairs
A- Acetic acid (CH3COOH) , sodium acetate (CH3COONa).
B- Carbonic acid (H2CO3 ) and sodium bicarbonate (NaHCO3).
C- Sodium dihydrogen phosphate (NaH2PO4 ) and Disodium hydrogen
phosphate (Na2HPO4 ).
D- Ammonium hydroxide (NH4OH ) and ammonium chloride (NH4Cl).
E- Proteins or amino acids.

26. 26
Buffering
The tendency of the solution to resist a change in pH following addition of
a strong acid or base .

27. 27
How do buffers “work”?

28. 28
Example of buffering by
acetate buffer pair (CH3COOH, CH3COONa)
HCl
(strong acid)
+ CH3COONa NaCl CH3COOH
( neutral salt) (weak acid)
+
If strong acid like hydrochloric acid (HCL) is added

29. 29
Example of buffering by
acetate buffer pair (CH3COOH, CH3COONa)
NaOH
(strong base)
+ CH3COOH CH3COONa
(salt)
+ H2O
(water)
If a strong base like sodium hydroxide NaOH is added

30. 30
Example of buffering by
ammonium bufferpair(NH4OH, NH4Cl)
HCl
(strong acid)
+ +
NH4OH NH4Cl
(salt)
H2O
(water)
If strong acid like hydrochloric acid (HCL) is added

31. 31
Example of buffering by
ammonium buffer pair (NH4OH, NH4Cl)
NaOH
(strong base)
+ +
NH4Cl NH4OH
(weak base)
NaCl
(salt)
If a strong base like sodium hydroxide NaOH is added

32. 32
Physiological buffers

33. 33
Physiological buffers
The buffer systems are “The life-saving devices'' of the body as:
 The pH of the blood must be kept within a very narrow range between 7.35 – 7.45
and this accomplished by the buffers of the blood.
 It can be stated in general that all reactions of living protoplasm take place in
buffer media.

34. 34
Physiologicalbuffers
Phosphate buffer
Hemoglobin
Proteins and amino acids
Bicarbonate buffer
Phosphate buffer
Hemoglobin
Proteins and amino acids

35. 35
1- Bicarbonate buffer (H2CO3 , NaHCO3 )
HCl + NaHCO3 H2CO3 + NaCl
If the acidity is raised , carbonic acid will dehydrate by carbonic anhydrase
enzyme to yield CO2 ,H2O which can escape through expiration.
If HCl is added to the media containing this buffer

36. H2CO3
Carbonic anhydrase
CO2 + H2O
H+ + HCO3
-
Increase Respiration rate
Co2 Decrease NaHCO3
Desrease NaHCO 3 leads to acidosis
N.B.:
If pH of the blood ever gets below 7 , this would be fetal
1- Bicarbonate buffer (H2CO3 , NaHCO3 )

37. 1- Bicarbonate buffer (H2CO3 , NaHCO3 )

38. 38
1- Bicarbonate buffer (H2CO3 , NaHCO3 )
NaOH + H2CO3 NaHCO3
+ H2O
Weak base
If a large amount NaHCO3 is formed, the excess bicarbonate is eliminated in urine.
If a strong base like sodium hydroxide NAOH is added
If a large amount of alkali is liberated in blood stream , the pH may raise to 7.4 – 7.5
and this condition is known as alkalosis (not common as acidosis).

39. 39
Alkali reserve
 The basic units of the blood that acting as buffers such as NaHCO3.
N.B.:
The ratio of bicarbonate to carbonic acid is normally 20:1

40. 40
Bicarbonate bufferis the most important buffer
1.Bicrbonate present in high concentration in the plasma
e.g. In human 25 mEq / liter at pH 7.4.
2.The carbonic anhydrase enzyme is present in RBCs and renal tubules
and allow the rapid inter conversion of carbonic acid to CO2 .

41. 41
Bicarbonate buffer is the most important buffer
3. The lungs regulate the partial pressure of CO2 in the blood on a minute by
minute basis.
4. The kidneys regulate urinary bicarbonate excretion and change the plasma
HCO3
- concentration slowly , over the course of hours .
5. Hemoglobin is positioned side by side with the carbonic anhydrase in
erythrocytes and favor the buffering action of bicarbonate .

42. 42
Physiologicalbuffers
Phosphate buffer
Hemoglobin
Proteins and amino acids
Bicarbonate buffer
Phosphate buffer
Hemoglobin
Proteins and amino acids

43. (The main buffer of urinary system)
HCl + Na2HPO4 NaH2PO4 + NaCl
A large amount of NaH2PO4 would contribute to an acidosis and the excess
of it will be eliminated in the urine.
Phosphate buffer (NaH2PO4 , Na2HPO4 )
If a strong acid like HCl is added to this system
`

44. 44
NaOH + NaH2PO4 Na2HPO4 + H2O
A large amount of Na2HPO4 would contribute to an alkalosis and the excess of it
will be eliminated in the urine.
2. Phosphate buffer(NaH2PO4 , Na2HPO4 )
If a strong base like NaOH is added to this system
`

45. 45
3. Hemoglobin buffer
HbO2 +
H+ HHb+
+ O2
Increased (H+ ) will drive the reaction to the right , conversely increased PO2 will
favours oxyhemoglobin formation.
 The histidine buffer of hemoglobin control the sudden additions of acid or
base.
 It is more powerful in the short run than the bicarbonate system

46. 46
4.Proteins andAmino acids
 Proteins act as one of the most important buffer systems in blood and tissues.
 Their buffering ability derives from the dissociable groups on their constituent
amino acids.

47. 47
Therefore , glycine can present in three forms depending on the pH:
1.Completely protonated (COOH-CH2-NH3
+) , Net charge is positive.
4.Proteins and Amino acids
2- Protonate amino group with unprotonate caroxyl group
(COO--CH2-NH3
+), the net charge is zero and this is isoelectric point of glycine.
3.Completely unprotonaed (H2N-CH2-Coo- ), net charge is negative.
From above, the amino acids and proteins can accept or donate a proton very easily when
an acid or base are added.

48. 48
N.B.:
Histidine (pKa = 6) is the only amino acid with significant buffering capacity in the
physiological pH range (6 – 8)
4. Proteins and Amino acids

49. Acid - Base balance

50. Acid - Base balance
Acid - base balance refers to the mechanisms the body uses to keep its fluid close to
normal pH so that the body can function normally.

51. Acid – Base Regulation
 Buffering agents
 Respiratory system
 Renal system
The body has three lines of defense to regulate the body's acid - base balance and
maintain the blood pH normal:

52. Acid-Base imbalance

53. Acid-Base imbalance
Alkalosis
Acidosis
Is defined as an arterial
pH below 7.35
is defined as an arterial
pH above 7.45

54. Acidosis/Alkalosis
Primary respiratory Primary metabolic
Disturbance in CO2 level Disturbance in bicarbonate level

55. Acidosis

56. Causes:
1. Acute pulmonary insufficiency
( e.g asthma , pneumonia , pulmonary embolism)
2. Chronic pulmonary insufficiency
( e.g chronic obstructive pulmonary disease)
It exists when there is acidosis with hypercapnia (pCO2>45mmHg)
Primary respiratory acidosis

57. Causes:
1. Diarrhea
2. Carbonic anhydrase inhibitors
3. Lactic acidosis
4. Keto-acidosis in diabetes or in alcoholism
5. Aspirin poisoning
It is characterized by a low serum level of bicarbonate (less than 22mEq / liter)
Primary metabolic acidosis

58. 1- Bicarbonate buffer (H2CO3 , NaHCO3 )

59. Alkalosis

60. Causes:
1. Hyperventilation due to severe anxiety, in patients on respirators
2. Fever
3. In high altitudes
It occurs when there is alkalosis with hypocapnia (pCO2 < 35mmHg)
Primary respiratory alkalosis

61. Causes:
1. Loss of gastric HCl without loss of pancreatic HCO3
e.g. vomiting
2. The administration of some diuretics
It occurs when a high serum bicarbonate level (>29 mEq / liter)
Primary metabolic alkalosis

62. The two organs in the body serve as a compensatory function to maintain
acid base balance:
In case of metabolic acidosis or alkalosis
In case of respiratory acidosis or alkalosis
By retention or elimination of CO2
By retention or elimination of HCO3
-
Acidosis and alkalosis compensation

64. Acidosis and alkalosis compensation
Complete
compensated
If pH brought back
within normal level
Partial
compensated
If pH range is still
outside normal level
Uncompensated
If the body does not try to
restore pH to normal level

65. How are acid base disorders diagnosed?

66. 1) Partial pressure of oxygen (PaO2)
2) Partial pressure of carbon dioxide (PaCO2)
3) pH
4) Bicarbonate (HCO3)
5) Oxygen content (O2CT) and oxygen saturation (O2Sat) values
Arterial Blood Gases
ABG measures:
An arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon
dioxide in the blood from an artery. This test is used to check how well your lungs are able to
move oxygen into the blood and remove carbon dioxide from the blood.

67. Arterial Blood Gases
Normal reference ranges:
pH: 7.35-7.45
HCO3
-: 22-29 mEq /L (mmol/L)
mmHg
35-45
:
pCO2

68. What is your assessment?
Acid - base imbalance cases

69. Baby was rushed to the emergency room following her mother’s complaint that the
infant has been difficult to feed and has had diarrhea for the past 3 days , the infant's
respiratory rate is elevated .
The physician orders ABGs (Arterial blood gases) , the results show:
pH 7.37 , pCO2 27 mmHg and HCO3
- 19 mEq/L
 what is your assessment with explain ?
Acid – base imbalance cases

70. Steps of interpretation
1. Identify if it is acidosis/alkalosis
2. Identify if it is respiratory/metabolic
3. Identify if it is compensated (full/partial) / uncompensated

71. Steps of interpretation
Baby was rushed to the emergency room following her mother’s complaint that the infant
has been difficult to feed and has had diarrhea for the past 3 days , the infant's respiratory
rate is elevated .
1. Case history
2. ABGs results
pH 7.37 (normal) acidic side
pCO2 27 mmHg (less than normal)
HCO3
- 19 mEq/L (less than normal)

72. Answer of case with explanation
A. Fully compensated Primary metabolic acidosis
Explanation:
This due to case history of diarrhea for long period leads to loss of bicarbonate and
decrease than normal level .
The body compensation occurs by increase respiratory rate and loss of CO2 and body
success to return pH to normal .
Acid – base imbalance cases

73. ACID - BASE BALANCE