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CO2 Transport ~5 ml CO2/ 100 ml systemic venous blood ~20% of CO2 carried as carbamino-Hb (HbCO2) H N Hb H H N HbCO2 COOH ~80% of CO2 carried in solution in plasma as HCO3C.A. CO2 + H2O HCO3- + H+ H2CO3 SLOW! fast Blood is in tissue capillaries for only 5 seconds! C.A. = Carbonic anhydrase •found in virtually all phyla •in human, in RBC 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. Central Regulation of Ventilation • Examine neural control of breathing • Respiratory centers in the brain • Peripheral input to respirator centers 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 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+ Trout - Environmental Hypoxia PO2 (mm Hg) Breathing rate (min-1) Ventilation vol. (ml•min-1) • VO2 (ml O2•kg-1•h-1) Blood lactate (mg•100ml-1) Aerated Hypoxic 155 30 85 120 500 3500 100 100 12.77 34.86 Lactate Pathway NADH NAD+ pyruvate lactic acid LDH lactate + H+ LDH = lactate dehydrogenase ½O2 lactic acid H2O pyruvate Additional O2 required after cessation of exercise to “repay the O2 debt” Alternative Anaerobic Pathways 1) Succinate/propionate pathway Glucose PEPCK PEP PK (= pyruvate kinase) pyruvate oxa acetyl-CoA mal oxa citrate H+ fum suc mal TCA suc-CoA fum suc PEPCK = phosphoenolpyruvate carboxykinase a-KG 2 NADH PEPCK 2 PEP 2 ADP 2 NAD+ 2 OXA 2 ATP 2 SUC 2 ADP 2 ATP CoA 2 ATP 2 ADP 2 SUC-CoA Advantages: • +4 ATP to SUC • +4 ATP to propionate • useful - fatty acids • less acidic than l.a. 2 ADP 2 Me-MAL-CoA 2 ATP CO2 2 propionyl-CoA 2 ADP 2 ATP CoA 2 propionate