1 / 72

ACID BASE BUFFERS

ACID BASE BUFFERS. Dr Nithin Kumar U Assistant Professor Biochemistry, YMC. ACIDS. Acids are substances which are:- proton donors (Lowry-Bronsted Theory) electron acceptors (Lewis Concept) dissociate to give hydrogen ions ( Arrhenius concept ) HA H + + A -

karlae
Download Presentation

ACID BASE BUFFERS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ACID BASE BUFFERS Dr Nithin Kumar U Assistant Professor Biochemistry, YMC

  2. ACIDS Acids are substances which are:- • proton donors (Lowry-Bronsted Theory) • electron acceptors (Lewis Concept) • dissociate to give hydrogen ions (Arrhenius concept) • HA H++ A- • HCl H++ Cl-

  3. STRENGTH OF ACIDS Strong acids: • Dissociate/ ionize completely • HCl H++ Cl- Weak acids • Ionize incompletely • H2CO3 H++ HCO3-

  4. BASE Bases are substances which are:- • proton acceptors (Lowry-Bronsted Theory) • electron donors (Lewis Concept) • dissociate to give hydroxyl ions (Arrhenius concept) • NH3+H+ NH4 • NaOH Na++ OH-

  5. CONJUGATE ACID- BASE PAIR • HA H++ A- • HA ACID since it donates protons • A- BASE since it accepts the protons • HA and A- are called as conjugate acid – base pair

  6. CONJUGATE ACID- BASE PAIR

  7. DISSOCIATION CONSTANT • Dissociation is a reversible reaction • HA H++ A- • At equilibrium: (Undissociated/dissociated )is constant • Dissociation constant Ka= [H+]+ [A-] [HA]

  8. pH • pH = negative Logarithm of hydrogen ion concentration • pH= -log[H+] • pH= log{1/[H+]} • Higher the hydrogen ions concentration or acidity lower will be the pH value pH = - log [H+]

  9. pH • In pure water at 25o C, [H+] = 10–7 mol/L • Therefore, pH = negative log of 10–7 = 7

  10. pH Decreasing [H+] Increasing pH

  11. pH of some biologically important fluids

  12. pKa • The pH at which the acid is half ionized • Indicates the strength of the acid • strong acids – low pKa • weak acids – high pKa

  13. IMPORTANCE OF pH • pH affects the structure, properties and functions of biomolecules, proteins (enzymes) and nucleic acids • Small changes in pH can produce major disturbances in cell functions

  14. HENDERSON-HASSELBALCH EQUATION • Relates pH, pKa & concentrations of the acid , conjugate base of a buffer system • pH = pKa + log [base] [acid] • In solution weak acids dissociates • HA H++ A- • Dissociation constant: Ka= [H+]+ [A-] [HA]

  15. HENDERSON-HASSELBALCH EQUATION

  16. HENDERSON-HASSELBALCH EQUATION: Applications • To calculate any one of the four variables- pH, pK, [acid] or [salt], if other three are known • Assessment of acid-base status • Measurement of pH • Measurement of salt concentration • To understand and predict dissociation behavior of buffers and in preparation of buffers

  17. ACIDS GENERATED BY BODY METABOLISM Volatile acid • Carbonic acid (H2CO3) Carbonic anhydrase (in RBC) CO2+ H20 H2CO3 Non-Volatile acids • Lactic acid Sulphuric acid • Ketoacids Phosphoric acid • Role in H+ homeostasis/ acid-base balance in the body • Applied in separation, identification and quantitation of biomolecules in research and clinical laboratories

  18. ACID BASE BALANCE • Reference range of pH = 7.35 -7.45 • Acidosis = pH < 7.35 CNS depression, coma • Alkalosis = pH > 7.45 neuromuscular hyper excitability, tetany • Life is threatened when plasma pH goes beyond: 6.8 - 7.8

  19. ACID BASE BALANCE & DISORDERS

  20. REGULATION OF BLOOD pH • FIRST LINE DEFENCE - Bicarbonate Buffer Phosphate Buffer Protein Buffer Hb Buffer • 2nd LINE DEFENCE - RESPIRATORY MECHANISMS • 3rd LINE DEFENCE - RENAL MECHANISMS

  21. ACID BASE BALANCE Buffers: • First line of defense against change of pH. • Present in blood, ICF and urine/renal tubular fluid. • Act immediately when a change in pH occurs. • Effect is temporary- do not eliminate acids or bases from the body.

  22. ACID BASE BALANCE Respiratory system: • Lungs eliminate CO2 by expiration. • Takes few minutes for compenastion • compensation is not complete or permanent Renal system: • Permanent • Non-volatile acids are excreted by kidney takes hours to few days to fully compensate any acid-base imbalance

  23. BUFFERS • The solutions that resist changes in pH when acid or alkali is added to them • Mixture of weak acid with its salt with a strong base Ex: CH3COOH/CH3COONa • Mixture of weak base with its acidic salt Ex: Na2HPO4/NaH2PO4

  24. BUFFERS

  25. BUFFERS: MECHANISM OF ACTION • When acid is added – salt component will take up the H+ ions & forms the weak acid • Ex: Acetate Buffer CH3COOH/CH3COONa HCl + CH3COONa CH3COOH+NaCl

  26. BUFFERS: MECHANISM OF ACTION • Base is added – the acid component will react with it & forms the weak base & water. • Ex: Acetate Buffer CH3COOH/CH3COONa NaOH+ CH3COOH CH3COONa+H20

  27. MECHANISM OF BUFFERING • Buffer systems take up H+or release H +as conditions change Strong acid (H+) added Strong alkali (base) added

  28. BUFFERING CAPACITY • The amount of strong acid or strong alkali required to be added to buffer to bring about a unit change in pH It depends on: • pKa value • Ratio between the salt to acid concentration (molar concentration of the buffer ) • Buffering capacity is maximum when the pH of the buffer is equal to its pK value

  29. BUFFERS: EFFECTIVENESS • In a buffer, when [salt] = [acid] : pH = pK + log 1 pH = pK + 0 pH = pK • A buffer has maximum buffering capacity and is most efficient, when pH of the soln. = its pK value

  30. BUFFERS: EFFECTIVENESS A buffer is most effective when: • pH = pKa or [salt] = [acid] • ↓pKa ↑H+↑HCO3/H2CO3 ↑effectiveness of buffer

  31. BUFFERS: Example Buffer Acid Conjugate base/Salt pK • Phosphate Buffer H2PO4– HPO4– – 6.8 (HPO4– – + H2PO4–) • Bicarbonate Buffer Carbonic acid Bicarbonate 6.1 (HCO3–+ H2CO3) H2CO3 HCO3– • Protein Buffer H+-Protein Protein (Protein + H+-Protein)

  32. BUFFER SYSTEMS IN THE BODY

  33. BUFFERS: IMPORTANCE • Role in H+ homeostasis/ acid-base balance in the body • Applied in separation, identification and quantitation of biomolecules in research and clinical laboratories

  34. ACID BASE BALANCE

  35. BICARBONATE BUFFER • Counts for 65 % of buffering capacity in plasma • pKa : 6.1 • Components: Bicarbonate (NaHCO3) Carbonic acid (H2CO3) • represents a high alkali reserve- for buffering against acids • The ratio of NaHCO3to H2CO3phosphate is 20:1 • Plasma Bicarbonate levels: 22 – 26 mmol/Lit • Plasma levels of H2CO3 is 1.2 mmol/L

  36. BICARBONATE BUFFER: MECHANISM OF ACTION IN ACIDOSIS CO2 Exhaled H2O + CO2 H2CO3 H++ HCO3- CA Acids H+ HCO3Reabsorbed H2CO3/HCO3

  37. BICARBONATE BUFFER: MECHANISM OF ACTION IN ALKALOSIS HCO3 Excreted H2O+ HCO3 Bases OH+ H2CO3 Regained OH-+ H2CO3 H2CO3/HCO3 CO2 Retains

  38. PHOSPHATE BUFFER • Intracellular buffer • Effective at a wide pH range • More than one ionizable groups H3PO4H+ + H2PO4- (pKa = 1.96) H2PO4 H++ HPO4-- (pKa = 6.8) HPO4 H + + PO4 ---(pKa = 12.4)

  39. PHOSPHATE BUFFER: COMPOSITION • Sodium dihydrogen Phosphate (NaH2PO4) - acidic • Disodium Monohydrogen Phosphate (Na2HPO4)- basic • pKa= 6.8 • pH = pKa + log [base] / [acid] • The ratio of base to acid phosphate is 4:1

  40. PROTEIN BUFFER • Intracellular buffer • Ionizable side chains • Side chain with pKa nearer to the physiological pH – act as a buffer. • pKa of Imidazole group of the Histidine: 6.1

  41. HEMOGLOBIN BUFFER • Function: transport of O2 & CO2 • RBC need a buffer system to combat acid base derangements occurring during gas transports • Hb a buffer in RBC • Buffering action: imidazole group of histidine • Enzyme: Carbonic anhydrase

  42. HEMOGLOBIN BUFFER @ TISSUE CO2 TISSUES CO2 + H2O H2CO3 H+ + HCO3- TISSUES CA CO2 RBC O2 Cl- O2 Cl- Hb HCO3-

  43. Hb Hb O2 O2 H H Hb Hb HEMOGLOBIN BUFFER @ LUNG PHOSPHATE BUFFER: COMPOSITION O2 O2 H++ HCO3 H++ HCO3 CO2 CO2 CO2 CO2 RBC RBC H2CO3 H2CO3 CA CA CO2 + H2O CO2 + H2O

  44. RESPIRATORY MECHANISMS • 2nd Line of defense against acid base imbalance • pH is regulated by altering respiratory rate changing the CO2 levels • Normal pCO2 =35 - 45 mm Hg • Acidosis: hyperventilation • Alkalosis: hypoventilation

  45. RESPIRATORY MECHANISMS: ACIDOSIS Chemoreceptors Peripheral – Aorta, Carotid Arteries Central – Medulla Oblongata Acidosis: High H+ Stimulate the Respiratory Centre pH returns to Normal Increased Rate & Depth of Respiration ( hyperventilation) ↓ H + + HCO3 Expulsion of more CO2 ↓H2 CO3 ↓pCO2 of blood

  46. RESPIRATORY MECHANISMS: ALKALOSIS Chemoreceptors Peripheral – Aorta, Carotid Arteries Central – Medulla Oblongata Alkalosis: Low H+ Inhibits Respiratory Centre pH returns to Normal Decreased Rate & Depth of Respiration ( hypoventilation) ↑ H + + HCO3 Retention of more CO2 ↑H2 CO3 pCO2 increases

  47. RENAL MECHANISMS • Takes hours to days to act • Can eliminate large amounts of acid • Can also excrete base • Can conserve and produce bicarbonate ions • Most effective regulator of pH • If kidneys fail pH balance fails

  48. RENAL MECHANISMS • Excretion of H+ ions • Excretion of H as titrable acid • Reabsorption of Bicarbonate • Excretion of Ammonium ions

  49. RENAL MECHANISMS: EXCRETION OF H+ • Site: PCT • Increase the alkali reserve • Generation of HCO3 • Mediated by Na-H exchanger • Potassium competes with H+ for Na-H exchanger

  50. RENAL MECHANISMS: EXCRETION OF H+

More Related