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CO2 Transport
~5 ml CO2/ 100 ml systemic venous blood
~20% of CO2 carried as carbamino-Hb(HbCO2)
HN
H
N
H
COOH
Hb HbCO2
~80% of CO2 carried insolution in plasma as HCO3
-
fastSLOW!
CO2 + H2O H2CO3 HCO3- + H+
Blood is in tissue capillaries for only 5 seconds!
C.A.
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- exchangerWhen 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
•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 reconvertingNADH to NAD+
Under anaerobic conditions:
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
lactic acid pyruvate
½O2 H2O
Additional O2 required aftercessation of exercise to
“repay the O2 debt”
Alternative Anaerobic Pathways
1) Succinate/propionate pathway
Glucose
PEPpyruvate
acetyl-CoA
citrate
-KG
suc-CoA
suc
fum
mal
oxa
TCA
PK
oxa
mal
fum
suc
PEPCK
PEPCK = phosphoenolpyruvate carboxykinase
(= pyruvate kinase)
H+