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

pyruvate lactic acid

lactate + H+

NADH NAD+

LDH

LDH = lactate dehydrogenase

Lactate Pathway

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+

2 PEP 2 OXA 2 SUC

PEPCK

2 ADP 2 ATP 2 ADP 2 ATP

2 SUC-CoA

2 Me-MAL-CoA

2 propionyl-CoA

2 propionate

CoA2 ATP

2 ADP

CoA

CO2

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.

2 NADH 2 NAD+