buffers physiological buffers bicarbonate/carbonic acid buffer system protein buffer system phosphate buffer system

1. PHYSIOLOGICAL
BUFFERS
Mary Theresa
MSc. Microbiology

2. Acid
According to Bronsted-Lowry concept,
• Acid- substance that gives off protons- proton (H+) donor
• Base- substance that accepts protons- proton acceptor.
• An acid dissociates to form proton and base.
• A strong acid has a weak base while a weak acid has a strong
base.

3. Alkalies
• Strong base that dissolves in water.
• pH > 7.0
• Dissociates to form metallic ion and OH- ions.
• Eg: Metallic hydroxides such as NaOH and KOH.

4. BUFFERS
• Solutions that resist change in pH on the addition of small
amounts of acids or bases by binding or releasing H+ ions.
• A buffer consist either of a weak acid and its conjugate base.

5. PHYSIOLOGICAL BUFFERS
• Buffers whose pKs are near the normal blood pH.
• WHY DOES THE BODY HAVE BUFFER SYSTEM?
• In blood maintain a pH close to 7.35-7.45; a change in the pH
blood affects the uptake of oxygen and cellular processes.
• Cellular metabolism- yields acids.
• Production of basic compounds- negligible except for a small
quantity of bicarbonates.
• Important in proper functioning of cells and blood.

7. BICARBONATE/CARBONIC ACID BUFFER SYSTEM
• Most important & predominant extracellular buffer system in
the body.
• pK=6.1
• Carbonic anhydrase/ carbonate dehydratase.
• Carbonic acid- weak acid.
• Bicarbonate ions- conjugate base.

8. Physiological mechanism
CO2; by- product of cellular respiration
dissolves in blood
taken by RBC cells

9. hydrated to carbonic acid by carbonic anhydrase
Dissociates into bicarbonate ions and hydrogen ions
Bicarbonate ions transported to lungs by binding with Hb

10. Dehydrated to CO2
Released during exhalation

11. • What happens to H+ ions?
• Bicarbonate to carbonic acid ratio= 20:1
• Alkali reserve- responsible for the effective buffering of H+ ions,
generated in the body.
• Homeostasis – pH sensors in medulla oblongata and kidneys.
• Respiratory compensation
• Le Chatlier’s principle
• Renal compensation

13. Medical conditions associated with blood pH
ACIDOSIS
• Blood pH goes DOWN (becomes acidic)
• [H+] increases; pH decreases (pH <7.35)
• Renal compensation
• Two types:
Metabolic Acidosis- due to decrease in bicarbonate- faster respiration
Respiratory Acidosis- due to increase in carbonic acid- slower respiration
• [CO2] increases
• Equilibrium shifts to RIGHT

14. Major clinical causes of acidosis
Metabolic acidosis
Diabetes mellitus (ketoacidosis)
Renal failure
Lactic acidosis
Severe diarrhea
Renal tubular acidosis
Respiratory acidosis
Severe asthma
Pneumonia
Cardiac arrest
Chest deformities

15. ALKALOSIS
• Blood pH goes UP (becomes alkaline)
• [H+] decreases; pH increases (pH>7.45)
• Two types:
Respiratory Alkalosis- due to decrease in carbonic acid- faster respiration
Metabolic Alkalosis- due to increase in bicarbonate- slower respiration
• [CO2] decreases
• Equilibrium shifts to LEFT

16. Major clinical causes of alkalosis
Metabolic alkalosis
Severe vomiting
Hypokalemia
Respiratory alkalosis
Hyperventilation
Anemia

17. PROTEIN BUFFER SYSTEM
• Mainly an intracellular buffer system.
• More concentrated than either bicarbonate or phosphate buffers.
• Behaves as a buffer in both plasma and cells.
• Plasma proteins- 2% of the total buffering capacity of the plasma.
• Excellent buffers- contain both acid and base groups that can give
up or take up hydrogen ions.
• The ability of proteins to serve as buffers depend on their amino
acid composition.

18. • The imidazole group of histidine- most effective contributor of
protein buffers.
• Haemoglobin- most important protein buffer.
• Haemoglobin- transport oxygen from lungs to tissues and carbon
dioxide back.
• At the tissue level, Hb binds to H+ ions and helps to transport CO2 as
bicarbonate ions with a minimum change in pH- Isohydric
transport.
• In lungs, Hb combines with O2, H+ ions are removed and combines
with bicarbonate ions to form carbonic acid, which dissociates to
release CO2.

19. PHOSPHATE BUFFER SYSTEM
• Intracellular buffer system.
• Less importance in plasma- low concentration (3mg/100ml).
H2PO4
-(aq) H+(aq) + HPO4
2-(aq)
• dihydrogen phosphate ions(H2PO4
-) and monohydrogen phosphate ions
(HPO4
2-)- constitute major components.
• H2PO4
- proton donor (acid) and HPO4
2- proton acceptor (base).
• As in the bicarbonate system, reactions that proceed to the right release H+
ions and pH goes down, and those to the left pH increase.
• Phosphates are major anions in intracellular fluid & minor anions in
extracellular fluid.

20. • Monohydrogen phosphate is formed when dihydrogen phosphate
(weak acid) combines with a strong base, such as OH- ions.
• Dihydrogen phosphate is produced in the presence of excess H+
ions in kidney tubules that then combines with monohydrogen
phosphate.

21. • Ratio of base to acid=4:1
• In the extracellular environment- sodium hydrogen phosphate
(Na2HPO4) and sodium dihydrogen phosphate (NaH2PO4) act as
the important buffer constituents.
• But, inside the cell- potassium hydrogen phosphate (K2HPO4)
and potassium dihydrogen phosphate (KH2PO4) predominate.

22. REFERENCES
• CHEMISTRY FOR THE SCIENCE- the essential concepts.3rd
edition. Jonathan Crowe & Tony Bradshaw;2010. Oxford
university press: 606-640.
• BUFFER SYSTEMS by Sriloy Mohanty.
• ACID-BASE BALANCE by Jayprakash.
• PHYSIOLOGY BIOCHEMISTRY by K Vijayakumaran Nair.
• BIOCHEMISTRY by U.Satyanarayana and U.Chakrapani.