O2 and CO2 Transfer Between Alveolus, Blood and Tissue Flashcards
What are the two ways oxygen can be carried in the blood?
Physical
Chemical
How is O2 carried physically in the blood?
plasma soluble (2%) 0.3ml O2/100ml blood
How is O2 carried chemically in the blood?
O2 bound to hemoglobin (98%)
How much O2 does Hb bind?
1.34ml
How much hemoglobin is there per 100ml blood?
15g
What is the O2 carrying capacity of Hb?
20mls O2/100ml
What is the total arterial content of O2?
20 + 0.3ml = 20.3 ml O2/100ml blood
What is the total venous O2 content?
O2 carrying capacity is 15mls/O2/100mls and plasma soluble 0.28mls
15.28ml O2/100ml blood
How are SaO2 calculated?
Oxyhemoglobin/O2 carrying capacity of Hb
What is the problem with SaO2?
it can remain the same even if the O2 content of the blood differs i.e. anemia or polycythemia
What is the P50 value on the oxygen dissociation curve?
the PO2 required for half maximal Hb saturation
What saturation does venous blood enter the alveolus?
75%
What does the arterial plateau phase ensure?
maximal HbO2 saturation even if alveolar PO2 is below normal
What does the steep phase of the curve favour?
offload of arterial oxygen to tissues
What happens when there is a left shift in P50 for the ODC?
increased Hb-O2 affinity and reduced offloading to tissue
Where might a left shift in the ODC be seen?
fetal Hb
What happens when there is a right shift in P50 for the ODC?
decreased Hb-O2 affinity and raised offloading to tissues
Where might a right shift in the ODC be seen?
high altitude
What may cause a right shit in the ODC?
stressors such as acidosis, fever and hypoxia
Describe the structure of hemoglobin
heterotetramer with 2a and 2b subunits
4 iron binding heme domains
O2 reversibly binds the Fe3+ ions in the centre of the heme ring
What alters the affinity of hemoglobin for O2?
CO2
2,3 BPG
interact with charged amino acids between the a and b subunits
What does hemoglobin require for each 2O2 released?
H+ ion
What interaction is pH and O2 sensitive?
amino terminus of a subunit binds b-carboxyl terminal histidine stabalising Hb structure
What happens to the interaction a physiological pH?
O2 binding to heme can release the protons to produce Oxy-Hb
What happens to the interaction in acidosis?
decreased pH favours the a-b subunit interaction and reduces the binding of O2 to heme
What are the two ways increased blood pCO2 releases O2 from Hb?
production of carbonic acid in red cell
Carbamate reaction at the N-terminal amino groups on the Hb a-subunit
What is the reaction produced for carbonic acid?
CO2 + H2O -> H2CO3 -> HCO3 + H
What is the reaction produced for carbamate reaction?
CO2 + R-NH2 -> R-NH-COO + H
What is the overall effect of increased blood pCO2?
acid stabilisation of a-b B subunits and a low affinity for O2
What are the other factors affecting O2 transport?
Carbon monoxide - far greater affinity than O2 - HbCO, causing left shift
Anemia - O2 carrying capacity is lowered - shift right
What PO2 does fetal development occur at?
30mmHg
What ODC does the fetus have compared with the mother?
left shifted ODC - so high affinity for O2
How does the fetus allow for O2 off-loading?
very low PO2 at tissues
What Hb subunit is expressed during fetal development and when does this change?
y subunit
replaced at birth by bHb
What are the physical forms of CO2 in the blood?
Soluble CO2 5%
Bicarbonate ion 90%
What is the chemical form of CO2 in the blood?
carbamino hemoglobin
What is the amount of CO2 exhaled?
4ml CO2/100ml blood
How is the plasma pH buffered by the red cell?
HCO3 moves out of the red cell to maintain CO2 gradient and plasma pH
What is the Haldane effect?
Where deoxygenation of blood improves carriage of CO2
What is the first stage in CO2 release from tissue and O2 release from the RBC?
CO2 dissolves into plasma and red cell along partial pressure gradient
What is the second stage in CO2 release from tissue and O2 release from the RBC?
low tissue O2 favours CO2 carriage by blood - HALDANE
What is the third stage in CO2 release from tissue and O2 release from the RBC?
Carbamate reaction reduces HbO2 affinity - BOHR
What is the fourth stage in CO2 release from tissue and O2 release from the RBC?
Carbonic anhydrase reaction generates carbonic acid which protonates. HCO3 leaves cel and maintains CO2 gradient
What is the final stage in CO2 release from tissue and O2 release from the RBC?
Increased H in RBC reduces HbO2 affinity - BOHR
What is the first stage in CO2 release from RBC and O2 release from the Alveolus?
O2 dissolves into plasma along partial pressure gradient
What is the second stage in CO2 release from RBC and O2 release from the Alveolus?
High affinity of Hb for O2 reverses carbamation and protonation raising availability of high affinity Hb - BOHR
What is the third stage in CO2 release from RBC and O2 release from the Alveolus?
CO2 diffuses into alveolus according to partial pressure gradient. High PO2 reduces CO2 affinity for Hb - HALDANE
What is the fourth stage in CO2 release from RBC and O2 release from the Alveolus?
Movement of CO2 out of RBC increases HCO3 uptake
What is the final stage in CO2 release from RBC and O2 release from the Alveolus?
Proton release from Hb and increased HCO3 drive reverse carbonic anhydrase reaction and maintain outward CO2 gradient and lower plasma bicarbonate
