Flashcards in O2 and CO2 Transfer Between Alveolus, Blood and Tissue Deck (49)
What are the two ways oxygen can be carried in the blood?
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?
How much hemoglobin is there per 100ml blood?
What is the O2 carrying capacity of Hb?
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?
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?
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?
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?
interact with charged amino acids between the a and b subunits
What does hemoglobin require for each 2O2 released?
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