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CO 2 Transport ~5 ml CO 2 / 100 ml systemic venous blood ~20% of CO 2 carried as carbamino-Hb

H. H. N. N. CO 2 Transport ~5 ml CO 2 / 100 ml systemic venous blood ~20% of CO 2 carried as carbamino-Hb (HbCO 2 ). H. COOH. Hb. HbCO 2. C.A. CO 2 + H 2 O. H 2 CO 3. HCO 3 - + H +. C.A. = Carbonic anhydrase found in virtually all phyla in human, in RBC.

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CO 2 Transport ~5 ml CO 2 / 100 ml systemic venous blood ~20% of CO 2 carried as carbamino-Hb

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  1. H H N N CO2 Transport ~5 ml CO2/ 100 ml systemic venous blood ~20% of CO2 carried as carbamino-Hb (HbCO2) H COOH Hb HbCO2

  2. C.A. CO2 + H2O H2CO3 HCO3- + H+ • C.A. = Carbonic anhydrase • found in virtually all phyla • in human, in RBC ~80% of CO2 carried in solution in plasma as HCO3- fast SLOW! Blood is in tissue capillaries for only 5 seconds!

  3. Choride shift - must maintain same number of positive and negative charges in cell. HCO3- / Cl- exchanger When HCO3- moves out, Cl- moves in. Reverse chloride shift - HCO3- / Cl- exchanger moves Cl- out of RBC and HCO3-in.

  4. Central Regulation of Ventilation • Examine neural control of breathing • Respiratory centers in the brain • Peripheral input to respirator centers

  5. Peripheral Input to Respiratory Centers • Pulmonary stretch receptors • Excited by inflation of the lungs • Protect against overinflation; not too important in regular breathing • Chemoreceptors • Located in aortic and carotid bodies, medulla • Sample pO2 and pCO2 in blood

  6. Under anaerobic conditions: • No O2 available as final e- acceptor • Reducing equivalents build up • TCA cycle no longer functional • Can’t use fats or proteins for energy • Can’t transfer reducing equivalents • across mitochondrial membrane • Reduced NADH builds up in cytoplasm • Lack of NAD+ limits glycolysis Need alternative pathway for reconverting NADH to NAD+

  7. Trout - Environmental Hypoxia Aerated Hypoxic PO2 (mm Hg) 155 30 Breathing rate (min-1) 85 120 Ventilation vol. (ml•min-1) 500 3500 • VO2 (ml O2•kg-1•h-1) 100 100 Blood lactate (mg•100ml-1) 12.77 34.86

  8. Lactate Pathway NADH NAD+ pyruvate lactic acid LDH lactate + H+ LDH = lactate dehydrogenase

  9. ½O2 H2O lactic acid pyruvate Additional O2 required after cessation of exercise to “repay the O2 debt”

  10. PEPCK oxa mal H+ fum suc PEPCK = phosphoenolpyruvate carboxykinase Alternative Anaerobic Pathways 1) Succinate/propionate pathway Glucose PK (= pyruvate kinase) PEP pyruvate acetyl-CoA oxa citrate a-KG mal TCA suc-CoA fum suc

  11. CoA 2 ATP 2 ADP 2 SUC-CoA 2 Me-MAL-CoA 2 ADP 2 ATP CO2 2 propionyl-CoA 2 ADP 2 ATP CoA 2 propionate 2 NADH 2 NAD+ PEPCK 2 PEP 2 OXA 2 SUC 2 ADP 2 ATP 2 ADP 2 ATP Advantages: • +4 ATP to SUC • +4 ATP to propionate • useful - fatty acids • less acidic than l.a.

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