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Gaseous transport in the blood

This informative text explores the gaseous transport in blood, focusing on oxygen transport forms, hemoglobin, and the oxygen dissociation curve. Learn about oxygenation, hemoglobin structure, and factors affecting oxygen affinity.

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Gaseous transport in the blood

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  1. Gaseous transport in the blood By Dr.M.B.Bhat.

  2. Gaseous transport • O2 consumption by body = 250ml/min • CO2 excretion by body = 200ml/min

  3. Oxygen transport

  4. Oxygen transport • 2 forms • Physical form –Dissolved form in plasma as simple solution • Chemical form –Combination with Hemoglobin

  5. Physical form (or) Dissolved form in plasma • Account for about 1 to 2 % of O2 transport • Solubility coefficient of O2 = 0.003 ml/dl/mm Hg • O2 content in arterial blood (PO2100mm Hg) = 0.3ml/dl (15 ml in whole blood of 5Liter) • O2 content in venous blood (PO2 40 mm Hg) =0.12 ml /dl (6 ml in whole blood)

  6. Significance of dissolved form • Dissolved form determine PO2 in the blood; which in turn determine O2 combining capacity of Hb. • When O2 carrying capacity of Hb is affected; as in the case of CO poisoning, with Hyperbaric O2 treatment, this form content is increased and provide necessary O2 for tissue

  7. Chemical form (oxy-hemoglobin) • Normal Hb level = 15gm/dl • With full saturation (100%) O2 carrying capacity of Hb = 1.34 ml/ gm of Hb • O2 carrying capacity of 100ml blood = • 1.34 x 15 = 20.1ml/dl (with 100% Hb sat.) • Arterial blood (PO2 of 97mm Hg) with 97.5% Hb saturation (due physiological shunt) = 19.8 ml/dl

  8. Hemoglobin (Hb) • Molecular weight = 68,000 • Consists of 4 Heme moieties (with a ferrous ion in each) & conjugate with 4 polypeptide chains • Each ferrous ion combine with a molecule of Oxygen • Each Hb molecule carry 4 molecule of O2 (Hb4O8) • Combination of O2 with Hb is oxygenation (not oxidation) • This oxygenation & de oxygenation are so rapid require <0.01sec

  9. O2 dissociation curve • Method of determination: • 5 ml of blood placed in 250 ml of tonometer • Fill the tonometer with known concentration of O2. • Shake for 20 minutes in water bath at 37.5oc • After that measure % of Hb saturation in the blood • The result of saturation is plotted against that ofPO2.

  10. Oxygenation of Hb • Combination of O2 with Hb depend on PO2. • The relationship between PO2 & Hb saturation is not linear but “sigmoid shape”. • The curve obtained by plotting the Hb saturations against their various PO2 is – Oxygen dissociation curve • (Or Oxy-Hb dissociation curve • Or Hb dissociation curve)

  11. O2 dissociation curve • Sigmoid in shape • Having three phases– • Phase 1 -- Slow ascend (between 0 to 10 mm Hg of PO2.) • Phase 2 --Steep ascend (between 10 to 50 mm Hg) & • Phase 3 -- Plateau (between 70 to 100 mm Hg of PO2.)

  12. 3 important points in O2 dissociation curve are -- Arterial point -- PO2 of 100 mm Hg & Hb saturation of 97,5% Venous point --PO2 of 40 mm Hg & Hb saturation of 75% P50 --PO2 of 28 mm Hg & Hb saturation of 50% P50 – is the partial pressure at which 50% Hb saturation occur When P50 – increases O2 affinity decreases

  13. Basis or Reason for sigmoid shape • Heme to Heme interaction • Configuration change of Hb

  14. Heme to Heme interaction • O2 combine with Hb in step by step involving each Heme moiety with Ferrous iron one after another • Oxy-form increases O2 affinity for Hb by 300 times • In each stage, the kinetic velocity of formation of oxy-Hb proportionately increases by 300 times in every step • Hb4 +O2 Hb4 O2 K1 (Equilibrium constant) • Hb4 +O2 Hb4 O4 K2 • Hb4 +O2 Hb4 O6 K3 • Hb4 +O2 Hb4 O8 K4 • K1 >K2 > K3>K4 (by 300 times in every step) • So, initial slow combination become steep & when reaches saturation becomes plateau

  15. Effect of configuration change of Hb • The configuration of Hb changes due to oxygenation & deoxygenation • In deoxygenated state –Hb is in tight form (& expel O2) –Hence called “T” Hb • In oxygenated state – Hb is relaxed form (accommodate more O2) –called “R” Hb • T-form is formed due to salt bridges connecting opposite charged amino acids of the polypeptide chains (with exposure of Histidine amino acids) • These salt bridges are broken by O2. • More & more entry of O2 brake more & more salt bridges & consequently more & more relaxed and accommodate more & more O2 till saturation occurs

  16. Advantages of sigmoid shape curve • Plateau phase –Helps to tide over atmospheric pressure variations in different environmental conditions • Steep phase –Helps to deliver more O2 in case of body’s requirement

  17. Factors shifting O2 dissociation curve to right (less O2 affinity) In the blood level -- • Increase in temperature • Increase in H+ ion concentration ( pH) • Increase in CO2 • Increase in 2,3-DPG level

  18. Bohr’s effect • Decrease O2 affinity due to decrease in pH of blood is called Bohr’s effect • Normally decrease in pH of blood occur due to increase in CO2 content of blood – Hence, increase in blood CO2 shifts the O2 dissociation curve to right can also be called Bohr’s effect.

  19. Significance of Bohr’s effect • Takes place at tissue level • Helps in unloading & O2 delivery to tissue • Most of Hb unsaturation (O2 delivery) to tissue occur due to decrease in PO2. • Extra 1 to 2% of unsaturation of Hb (and resulting O2 delivery) is due to increase in PCO2

  20. 2,3-Diphosphoglycerate (2,3-DPG) • Metabolic byproduct of glycolysis via Embden Meyerhof pathway in RBC itself • It is a highly charged anion • Bind with β-chain of Deoxy-Hb • HbO2 + 2,3-DPG  Hb-2,3-DPG + O2 • Increase in concentration of 2,3-DPG causing more & more O2 liberation • Thereby decrease oxygen affinity with Hb

  21. Factors decrease 2,3-DPG level • Acidosis (inhibit glycolysis) • Fetal Hb (γ-chain of fetal Hb has poor binding capacity for 2,3,DPG) • Stored blood (due decrease in metabolism)

  22. Factors increase 2,3-DPG level • Hormones –Thyroid hormone, GH & androgen • Exercise –increase metabolism • High altitude –(secondary due to alkalosis with half life of 6 hours) • Anemia • Diseases causing chronic hypoxia

  23. Factors shift O2 dissociation curve to left (increased affinity) • Decrease in temperature • Decrease in H+ ion concentration ( pH) • Decrease in CO2 level • Fetal Hb • CO poisoning

  24. Conclusion • Speed of combination of Hb with O2 takes place with half saturation of 0.07second • Hb saturation with O2 complete in 0.3sec. • RBC travel through pulmonary capillariesin about 0.75second • Reverse reaction of HbO2 Hb + O2 also rapid with half saturation of 0.004sec in solution & 0.038 second in RBC

  25. CO2 Transport • Arterial blood – • CO2 content (concentration) – 50 ml/dl • CO2 tension -- PCO2 of 40 mm Hg • Venous blood– • CO2 content (concentration) – 54 ml/dl • CO2 tension -- PCO2 of 45 mm Hg • A-V CO2 difference = 4ml/dl

  26. CO2 present in the blood in 3 forms Simple solution -- 7% Bicarbonate form (HCO3) – 70% Carbamino-compound -- 23% (Carbamino-Hemoglobin)

  27. Simple solution (Dissolved form in plasma) • Accounts for about 7% of CO2 transport • Solubility of CO2 is 20 times of O2 • CO2 in arterial blood -- with PCO2 of 40 mm Hg –2.4 ml/dl • CO2 in venous blood -- with PCO2 of 45 mm Hg –2.7 ml/dl

  28. Chloride shift (Hamburger phenomena)

  29. Tti

  30. Account for 70% of CO2 transport Formation of HCO3 is very slow in plasma & Rapid in RBC due to presence of Carbonic anhydrase (CA) 2/3rd of HCO3 formed in RBC enter into plasma by chloride shift (occurs rapidly & completed within one second) Accumulation of HCO3 & Chloride ions in RBC increases the osmolality of RBC leads to endosmosis of water Henceii venous blood RBC is slightly bulged & Hct of venous blood is slightly higher (about 3%) than arterial blood.

  31. Carbamino Hemoglobin

  32. Carbamino-Hemoglobin (Carbamino compound) • In general CO2 combine with proteins in the blood are called carbamino compound • CO2 combine with protein of Hb alone called carbamino hemoglobin • Accounts for 15 to 25% of total CO2 transport • CO2 combine with amino groups –as buffering mechanism • Hb is an effective buffer in pH range of 7 to 7.6 • Hb as protein has 6 times more buffering capacity than plasma proteins

  33. Haldane’s effect • Binding of O2 with Hb reduces CO2 affinity for Hb is called Haldane’s effect • Takes place at lung level • O2 tension at alveoli cause oxygenation of Hb and thereby decrease CO2 affinity for Hb & • Cause release of CO2 from blood into alveoli • Haldane’s effect account for 50% of CO2 release from the blood into alveoli • Out of 4ml/dl expelled – • 2ml due to P CO2 difference between blood & alveoli • Another 2ml is due to Haldane’s effect

  34. CO2-Dissociation curve

  35. Conclusion of CO2 transport • In Arterial blood with pH 7.4 – • Out of total 50ml of CO2/dl – • Dissolved form accounts for –3ml (7%) • Carbamino compound –13ml (25%) • Bicarbonate form –34ml (68%) • In the venous blood with 54ml of CO2 & pH 7.36 -- Out of 4ml of CO2/dl added into blood from tissue -- • Dissolved form –0.4ml (10%) • Carbamino compound –0.8ml (20%) • Bicarbonate form –2.8ml (70%)

  36. In the lungs about 4 ml of CO2 from each 100 ml of blood discharged into the alveoli This amounts to 200 ml of CO2 /minute expelled from the body This amount of CO2 is equivalent in 24 hours to over 12,500 meq. Of H+ ions.

  37. END

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