Physiological buffers new

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 b ase 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.

6. 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.

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

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

9. Dehydrated to CO 2 Released during exhalation

10. 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

11. 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 [CO 2 ] increases Equilibrium shifts to RIGHT

12. 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

13. 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 [CO 2 ] decreases Equilibrium shifts to LEFT

14. Major clinical c auses of alkalosis Metabolic alkalosis Severe vomiting Hypokalemia Respiratory alkalosis Hyperventilation Anemia

15. 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.

16. 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 CO 2 as bicarbonate ions with a minimum change in pH- Isohydric transport. In lungs, Hb combines with O 2 , H + ions are removed and combines with bicarbonate ions to form carbonic acid, which dissociates to release CO 2 .

17. PHOSPHATE BUFFER SYSTEM Intracellular buffer system. Less importance in plasma- low concentration (3mg/100ml). H 2 PO 4 - (aq) H + (aq) + HPO 4 2- (aq) dihydrogen phosphate ions(H 2 PO 4 - ) and monohydrogen phosphate ions (HPO 4 2- )- constitute major components. H 2 PO 4 - proton donor (acid) and HPO 4 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.

18. 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.

19. Ratio of base to acid=4:1 In the extracellular environment- sodium hydrogen phosphate (Na 2 HPO 4 ) and sodium dihydrogen phosphate (NaH 2 PO 4 ) act as the important buffer constituents. But, inside the cell- potassium hydrogen phosphate (K 2 HPO 4 ) and potassium dihydrogen phosphate (KH 2 PO 4 ) predominate.

20. 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 .