Exam #3: Transport of Oxygen & Carbon Dioxide Flashcards
What is the difference between dissolved oxygen & conjugated oxygen?
Dissolved= Only dissolved gas generates partial pressure
(0.3%)
Conjugated= conjugated to Hb
(99.7% –reserve to draw from/ buffer)
Describe the structure of HbA.
2x alpha chains
2x Beta chains
4x Heme groups that can bind 1 O2
Thus HbA can bind 4 O2 molecules
Describe the structure of heme.
A prophyrin ring
Fe++ reversible binds O2
What is methemoglobin?
Fe+++ instead of Fe++ heme
DOES NOT bind O2
What causes an increase in methemoglobin?
1) Oxidation of Fe++ to Fe+++ by nitrites & sulfonamides
2) Deficiency is methemoglobin reductase
Describe the structure and function of Fetal Hb.
2x Beta chains are replaced by gamma chains
Higher affinity for O2 than HbA facilitates oxygen movement to the fetus
What is Hemoglobin S?
- Cause of sickle cell disease
- Abnormal beta subunits
- Forms sickle- shaped rods in RBCs that occlude small blood vessels
- Lower affinity for oxygen
What is the oxygen binding capacity?
The maximum oxygen volume that can combine with Hb, which is dependent on
- Hb concentration
- binding properties
What is the oxygen content? What is the equation for oxygen content?
Actual amount of O2 per volume of blood
O2 binding capacity x SaO2 + Dissolved O2
How is oxygen content altered in anemia?
Decreased Hb decreases oxygen content
What factors determine oxygen delivery to the tissues?
Cardiac ouput
Oxygen Content
= CO x Oxygen content
Draw the oxygen dissociation curve.
Hb saturation % vs. partial pressure of oxygen
What are the important features of the oxygen dissociation curve?
- Little change in Hb saturation at high partial pressures of oxygen (arterial) vs. large changes at low partial pressure (venous, 40 mmHg)
- Under normal conditions 5 mL of oxygen delivered
- Hb sets upper limit on the tissue partial pressure of oxygen
- Hb automatically delivers O2 to tissues at a tight PO2 range
What is the P50 value?
PO2 at which Hb is 50% saturated
What happens when the P50 is larger?
Shift the oxygen dissociation to the right
- Weaker binding
- Hb releases O2 eaeier
What happens when the P50 is smaller?
Shift the oxygen dissociation to the left
- Tighter binding
- Hb release O2 harder
How does an increase in temperature shift the oxygen dissociation curve?
Shift to the right
Easy delivery of oxygen
How does hypothermia change the oxygen dissociation curve?
Left shift
Preserve oxygen
How does a decreased in pH shift the oxygen dissociation curve? Give some examples. What is this called?
Right shift
- Acidosis
- DKA
- CKD
“Acid Bohr effect”
How does an increase in pH shift the oxygen dissociation curve?
Left shift
What is the Co2 Bohr effect? How does high CO2 affect the oxygen dissociation curve?
Binding of CO2 to Hb reduces the affinity of Hb for O2 (right shift in curve)
- High Co2 in tissue
- Makes Hb let go of O2 in the tissue
What is 2,3-diphosphoglycerate (2,3-BPG)? How does it affect the oxygen dissociation curve & when is it increased?
End product of RBC metabolism that is increased in:
- Hypoxia
- High altitude
- Anemia
Increased= right shift
How is the 2,3-BPG concentration altered in stored blood? What is the impact?
Decreased 2,3-BPG in stored blood products means that there is an increase in O2 affinity; this can lead to decreased tissue perfusion in blood replacement therapy
Describe the toxic effects of CO.
CO binds Hb with 250x affinity
- PaO2 is roughly normal= no feedback that content is low
- No physical sign of hypoxemia aside from bright cherry red skin
