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Gaseous transport in the blood

Gaseous transport in the blood. By Dr.M.B.Bhat. Gaseous transport. O 2 consumption by body = 250ml/min CO 2 excretion by body = 200ml/min. Oxygen transport. Oxygen transport. 2 forms Physical form –Dissolved form in plasma as simple solution

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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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