CO2 transport Flashcards
What are the three forms in which Co2 is transported from tissues to lungs?
HCO3- (95%)
Carbaminohemoglobin - HbCO2 (5%)
Dissolved CO2 (5%)
How does CO2 arrive at the lung as HbCO2? Does it favor binding in taut or relaxed form Hb?
CO2 binds to Hb at the N-terminus of globin (not heme). Binds to taut form - O2 unloaded, at the tissues.
How does CO2 arrive at the lungs as HCO3-?
1) CO2 diffuses to intravascular space (has greater solubility in blood than O2) and then RBCs.
2) Carbonic anhydrase converts CO2+H2O –> H2CO3 –> H+ + HCO3-.
3) HCO3- is exchanged for Cl- (chloride shift) and is transported in the plasma, H+ is picked up by hemoglobin.
What is the relation between H+ and hemoglobin near the tissues? What is the Bohr effect?
H+ associates with Hb near the tissues (created by CO2 release).
- It shifts oxygen dissocation curve right, favoring unloading of O2.
Bohr effect is oxygen dissociation from Hb caused by increased H+ from tissue metabolism.
How is CO2 released into the lungs?
- Upon blood arrival to lung, oxygenation of Hb promotes dissociation of H+ from Hb.
- Chloride shift reverses, bringing bicarb into RBCs
- With increased H+, it soaks up bicarb and forms CO2, which diffuses out of RBCs and into the alveolus for expiration. This is called the Haldane effect.
What is the effect of high altitude on PaCO2?
Drop in PO2 (atm) - Drop in PaO2 - Incr in ventilation, results in decreased PaCO2 (blowing off more CO2). This leads to chronic incr in ventilation.
What is the effect of high altitude on EPO?
Increases, causing increased hematocrit and Hb.
What is the effect of high altitude on 2,3BPG?
Increases - binds to Hb so that O2 can release more oxygen.
What is the effect of high altitude on cellular changes?
Mitochondria increase.
What is the effect of high altitude on the kidneys?
Increases renal excretion of bicarb to compensate for respiratory alkalosis.
How does high altitude affect pulmonary vasculature?
Causes vasoconstriction due to chronic hypoxia.
How does high altitude affect cardiac tissue?
Causes RVH due to pulmonary vasoconstriction.
How does exercise affect CO2 production and O2 consumption?
Increases both.
How does exercise change ventilation rate?
Increases to meet increased O2 demand.
How does exercise change V/Q ratio?
Becomes more uniform as apical capillaries dilate, decreasing wasted apical ventilation.
