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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