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Blood Buffers

Blood Buffers. Objectives. Definition of acid, base and buffer Maintenance of H+ Buffer Systems for regulation of H+ The Henderson –Hassel Balch Equation Aci d- Base disorders : Acidosis and Alkalosis. Back to Basics:.

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Blood Buffers

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  1. Blood Buffers

  2. Objectives • Definition of acid, base and buffer • Maintenance of H+ • Buffer Systems for regulation of H+ • The Henderson –Hassel Balch Equation • Acid- Base disorders : Acidosis and Alkalosis

  3. Back to Basics: • An acid is a substance that increases H+ concentration, thus reducing pH. • A base is a proton acceptor ., bases decrease H+ concentrations and raise the pH.

  4. Acids are produced continuously during normal metabolism, although the blood concentration of free hydrogen ion ( H+) vary between narrow limits. • The acids handled by the body daily are about 20,000 mmol of volatile and 40- 80 mmol of non-volatile acids.

  5. Relatively constant H+ concentrations are important physiologically, as small changes in pH affect enzyme activity and thus metabolism. • The immediate defense against changing H+ concentrations is provided buffers, while excretion is regulated by adaptive responses in the lungs and kidney.

  6. The changes in ECF (H+) conc. or (pH) are regulated by : • Buffers: v. rapid temporarily traps acids or bases • Respiratory response: rapid gets rid of or retains CO2 • Renal response: slow excretes of fixed acids & retains or excretes HCO3-

  7. Acid Production in the Body

  8. Volatile Acids: • CO2: The product of oxidation of substrate for utilization, mainly CHO and fat, is carbon dioxide. • Although CO2 is not an acid, it dissolves in H2O to form H2CO3 ,so accumulation of CO2 may lower body pH . • As CO2 is excreted through lungs it can be viewed as being volatile acid

  9. CO2 H+ + HCO3- ↔ H2CO3 ↔ CO2 + H2O Removed by lungs

  10. Non Volatile Acids: • These are of 2 types: organic and inorganic

  11. Organic acids : • mainly lactic acid and ketone bodies. • Lactate is produced continuously from the anaerobic metabolism of glucose, particularly in erythrocytes( no mitochondria) and skeletal muscle (strenuous exercising) • These are converted to glucose in the liver

  12. Ketone bodies are formed of fatty acids metabolism in the liver • As organic acids are almost fully metabolized , under normal circumstances they contribute little to net acid excretion

  13. InorganicAcids: • They are two main sources, sulphur-containing amino acids and phosphorus –containing organic compounds.

  14. Oxidation of sulphyhydryl groups in cysteine and methionine results in the synthesis of sulphuric acid • while hydrolysis of phosphesters produces phosphoric acid. • Inorganic acidic anion must be excreted from the body by kidney

  15. Buffers • Buffers are solutions of weak acids or bases which contain both dissociated and undissociated forms.

  16. Buffers • Buffers limit the change of pH that would be caused by addition of strong acid or base • Buffers act effectively at pH = pK ( also its concentration determine its efficiency

  17. The conc. of H+ in blood is usually of ECF expressed as the negative logarithm10 (pH) = - log H • The pH of the ECF is 7.35-7.45 • It is molar concentration is 35-45 nmol/L

  18. Buffers in Blood and Intracellular Fluid • The main extracelluler buffers: • Carbonic – bicarbonate system • Hb (hemoglobin) • The main intracellular buffers • Proteins (Ptn) • Phosphate buffer system

  19. Buffer → H Buffer (base) (acid) H+ + HCO3-→ H2CO3 → CO2 + H2O H+ + HPO24 → H2 PO-4 H+ + Hb- → H.Hb H+ + Prot- → H.Prot

  20. Hemoglobin: • Plays an important role more than other proteins as a buffer due to : • Relatively high concentration • Relatively rich histidine (pk=7.0) • Role in transport of blood gases

  21. CO2 + H2O +HbO2 ECF Tissues CO2 O2 Erythrocyte CO2 Carbonic anhydrase HCO3- HCO3- +H+ Cl - Cl - O2 + HHb

  22. Carbonic Acid-Bicarbonate system: • High concentration • Ratio rapidly corrected by respiration • Components easily measured.

  23. All the blood buffers are in equilibrium and changes in (H+) that affects one system produce corresponding changes in the others. • H2CO3/ HCO3- proved the most appropriate to be used to investigate the acid –base status

  24. Back to Basics: • K: The relative strength of weak acids are expressed quantitatively as dissociationconstants, that express the tendency to ionize. • pK= is the pH at which equal quantities of acid and its conjugate base exit.

  25. Back to Basics: • HA↔ H+ + A- • K =[ H+][A- ] [HA]

  26. [ H+]= K [HA] [A-]

  27. Take the log of both sides: • Log [ H+]= logK [HA] [A-] Multiply through by -1 • -Log [ H+]= - log K -log [HA] [A-]

  28. pH = pK + log [A-] [HA]

  29. The Henderson- Hasselbalch eq. • pH = pK + log [A-] • [HA] • Note: we can replace H2CO3 for 0.03 xPCO2 • Where 0.03 is the solubility coefficient of CO2 and PCO2 is the partial pressure of CO2( since H2CO3 is in equilibrium with the dissolved co2

  30. IF A- = HA • pH = pK + log 1 • 1

  31. pH = pK + 0 so pK is the pH at which 50% of the acid is dissociated or it is a pH at which equal amounts of the acid and its conjugate base exist.

  32. For Carbonic Acid-Bicarbonate system: • 7.4 = 6.1 + log [HCO3-] • [H2CO3]

  33. For Carbonic Acid-Bicarbonate system: • 7.4 -6.1 = log [HCO3-] [H2CO3] 1.3 = log [HCO3-] [H2CO3]

  34. For Carbonic Acid-Bicarbonate system: [HCO3-] = 20/1 [H2CO3]

  35. Collection and transport of specimens: • Arterial blood specimens are the most appropriate. • Arterialized capillary blood could also be used. • It is essential for the capillary blood to flow freely with novasoconstrictionor sluggish blood • Patients must be relaxed • Blood is collected into containers that contain sufficient heparin as an anticoagulant • Specimens transferred to lab immediately better chilled on ice to avoid glycolysis

  36. Disturbance of the Acid-Base Status • Acidosis : pH < 7.4 HCO3- < 20/1 H2CO3- • ↓ HCO3- = metabolic • ↑ H2CO3- = respiratory • Alkalosis: • pH > 7.4 HCO3- > 20/1 H2CO3- • ↑ HCO3- = metabolic • ↓ H2CO3- = respiratory

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