2. Acid Base Balance in the body
Maintenance of pH in body fluids
Specially the blood
Normal Blood pH is
Metabolism constantly produce acids
Pose a threat to blood pH

3. Types of acids in the body
Volatile acid
Can leave solution and enter the atmosphere (e.g. carbonic acid)
Fixed acids
Acids that do not leave solution (e.g. sulfuric and phosphoric acids)
Organic acids
Participants in or by-products of aerobic metabolism

4. Common Acids produced in the body
Carbonic Acid
Lactic Acid
Phosphoric Acid
Sulphuric Acid
Aceto Acetic acid
Beta hydroxy butyric acid
Pyruvic Acid
Oxalic Acid

5. Medicine used in daily life
Are mostly in acid forms. for examples
Aspirin
Ponston
Antibiotics HCl
Anti acid medicine

6. These produce a change in pH
Immediate correction of pH is required.
If not done , poses threat to life
Change on either side of not greater than 0.2 pH unit is desirable and tolerable
Slight fall than 6.8 as seen in DKA may cause death
Slight rise than 7.8, may also cause death
Correction is done by body buffers.

7. Learning objectives Buffer, conjugate acids & bases.
Buffering actions & buffering capacity.
Factors which determine buffering capacity.
pKa values of some important physiological buffers and their role.

8. Buffers Buffers are important in biochemical processes,
whether in plasma or in the cytosol of cells.
Buffers assure biological reactions occur under conditions of optimal pH.
They do this by controlling the hydrogen ion concentration of solutions.

9. Importance of Buffers
Control of pH is an essential property of biological systems
pH of Human blood plasma is maintained between 7.35 – 7.45 within 0.2 pH. unit.
Values outside not compatible with life
Most enzyme catalyzing various intracellular and intercellular reaction, do so at some definite pH / within a very narrow range.

10. Importance of Buffers
Metabolic reactions constantly produce acids / bases but not in balanced amount.
Which causes a pH shift, not suitable for optimum activity.
This shift needs proper compensation.
This is accomplished in Biochemical system mainly by Buffers.

11. What is buffer?
A buffer solution is one that on the addition of an acid or alkali resists a change in pH.
Buffer solution consists of a mixture of weak Bronsted Acid and a salt of its conjugate base, e.g.
CH3COOH and CH3COONa or
NH4OH and NH4Cl

12. Principle Behind Buffer Action
Buffers are composed of weak acids and their salts.
A salt is the acid minus its proton.
Weak acids and their salts have two properties that are important for buffering action.
First, weak acids are a reserve of the protons that neutralize OH- and prevent the solution from becoming alkaline.

13. Principle Behind Buffer Action
Salts of weak acids are strong bases and prevent the solution from becoming acidic.
Both components are needed and both are interchangeable through the loss (or gain) of a single proton.

14. How Buffer solution controls change in pH
When alkali is added to a buffer solution, the un-dissociated Bronsted acid present in mixture ionizes and produces H+ ions. These H+ ions reacts with OH- of added alkali to form H2O CH3COOH + OH-  CH3COO- + H2O CH3COOH  CH3COO- + H+

15. A buffer’s power lies in its reserves.
A buffer is at optimal strength when there is an equal amount of HA and A- in solution.
This will only occur when the pH of the solution equals the pKa of the acid’s group.
Adding OH- causes the buffer to respond by calling on the reserve pool of HA. A- is formed at the expense of HA.

16. Buffer’s Power
This continues until all the excess OH- is neutralized. At the end the salt pool has increased (and the acid pool has decreased) by the same number of moles of base that were added.

17. OH- Neutralized OH- Reserve acid Reserve salt 11 moles 11 molesHA
Reserve acid
11 moles
Reserve salt
11 moles A-
OH-
Neutralized A-
OH- A- A- A- A-
6 moles moles

18. How Buffer solution controls change in pH (Contd.)
Addition of alkali facilitates further dissociation of the available CH3COOH to furnish additional proton, which counters the effect and thus no change in pH.

19. When acid is added to an acetate buffer.
H+ + CH3COO-  CH3COOH
Proton added (i.e. HCl) combines exceedingly rapidly with the CH3COO- ion present in buffer mixture (as Potassium Acetate) and net change in pH is very negligible.
This change in pH would have been very large if conjugate base were absent.

20. Buffer action or capacity of a buffer depend upon two factors
Molar concentration of buffer component have direct relationship with buffer capacity.
Buffer conc. is defined as the sum of the conc. of the weak acid and its conjugate base.
0.1M acetate buffer 0.05M of CH3COOH and 0.05 M of CH3COONa in one litre of H2O.
It could also contain M of CH3COOH and 0.035M of CH3COONa.

21. Ratio of the conc. of conjugate base to the conc. of the weak acid.
Buffer action or capacity of a buffer depend upon two factors. (Contd.)
Ratio of the conc. of conjugate base to the conc. of the weak acid.
Greater the conc. of weak acid, more the buffer will be effective to alkali addition and vice versa.

22. Buffer selection
Selection of a buffer to be effective at the desired pH
value, depends on pKa value of the conjugate acid
(weak acid), therefore
For a buffer to be effective at pH 5.0, we should select a weak acid having pKa value of 5.0 or close to 5.0
Buffer should be prepared with molar conc. of component high but compatible with other feature of the system.

23. Buffer selection
Too high conc. of salt frequently inhibits the activity of enzyme or other Physiological systems.
Solubility of the buffer components may also limit the conc. that can be employed.

24. pKa for some buffers commonly used in Biochemistry.
S.No
Compound
pKa 1
Pyrophosphoric Acid
0.9 2
Histidine
1.8 3
E.D.T.A
2.0 4
Citric Acid
3.1 5
Acetic Acid
4.7 6
Carbonic Acid
6.1 7
Triethanolamine
7.8 8
Tris HMAE
8.0 9
Diethanolamine
8.9 10
Ethanolamine
9.5

25. Important Physiological buffers
Many biological compounds have the ability to ionize
These include organic acids, amino acids, proteins, nucleotide etc.
pH of more biological fluid is near 7.0 and dissociation of most of these compounds is complete there.

26. Important Physiological buffers
pH control in animals is a complex phenomenon.
Buffers and active pH controlling elements are present in circulating blood. These are :
CO2 and HCO3,
NaH2PO4 and Na2HPO4
oxygenated and non oxy. forms of Hb.,
Plasma proteins.

27. Buffer Systems in Body Fluids
Figure 27.7

28. H2CO3  CO2 + H2O  H2CO3  H+ + HCO3-
It is the main buffer system of plasma and is responsible for removal of CO2 produced in the tissues during metabolism.

29. The Carbonic Acid-Bicarbonate Buffer System
Figure 27.9a, b

30. HPO4-2 / H2PO4- It is important buffer system of ICF. The pKa is 7
HPO4-2 / H2PO4- It is important buffer system of ICF. The pKa is 7.21, very near to physiological pH, very effective buffering capacity.

31. HHbO2  H+ + HbO2
HHb  H+ + Hb-
Main buffer system in RBCs, H+ ions liberated by H2CO3 are taken up by Hb in RBCs and change in pH is prevented.

32. Amino Acid Buffers
Figure 27.8