Transport of Oxygen Flashcards
What are the two forms that oxygen takes in the blood?
Dissolved and conjugated to Hb
In solution, which form of oxygen contributes to the partial pressure to drive diffusion?
Dissolved
What percent of oxygen is conjugated in the blood?
99.7%
Why do you need the 0.3% of dissolved oxygen in the blood?
Starts the diffusion
The conjugated form serves as a buffer
What are the two components of each heme group?
Porphyrin ring
Fe 2+
What is methemoglobin? Does it bind oxygen?
Fe 3+
No
What are the drugs/conditions that oxidize Fe 2+ to Fe 3+?
Nitrates and sulfonamides
deficiency of methemoglobin reductase
How is fetal Hb different from adult? What is the effect of this?
Has two gamma chains instead of two beta chains
Allows to take oxygen from mother HbA
What is HbS? Where is this found? What is HbS’s affinity for oxygen compared to HbA?
Sickle cell Hb
Replaces the Beta Hb in adults
Lower affinity
What happens in individuals in HbS? (2)
Intravascular hemolysis
Lower Ability to bind oxygen
What is the O2 binding capacity? What are the variables that this depends on?
The maximum O2 volume that can combine with Hb
Depends in [Hb] and binding property of Hb
What is the oxygen content? Formula?
Actual amount of O2 per volume of blood
O2 content = O2 binding capacity*[SaO2] +dissolved O2
What is the equation for oxygen delivery to tissues?
O2 delivery = Cardiac Output × O2 content = Cardiac Output × [Dissolved O2 + HbO2]
Oxygen delivery depends on what?
Cardiac Output and oxygen content
What is the shape of the oxygen dissociated Hb curve? (relates PO2 to Hb saturation %).
What is the significance of this?
Sigmoid
This allows for large changes in mmHg of PO2 before it affects oxygen saturation
How steep is the slope of the upper portion of the oxygen dissociation curve? What does this mean?
Very shallow
Means that a relatively constant Hb saturation is ensured despite wide
variations in PO2.
How steep is the slop around the middle portion of the oxygen saturation curve (~40 mmHg)? What is the significance of this?
Very steep
Allows for rapid uptake of oxygen by tissues
Under normal conditions, about how much oxygen is transported from the lugs to the tissues by each 100ml of blood flow?
5 ml
Increases in p50 value of the Hb dissociation curve translates to stronger or weaker bonding?
Weaker
Oxygen released more easily
How does increases in temperature shift the oxygen dissociation curve? (p50 value)?
Rightward (increases p50)
How do decreases in temperature shift the oxygen dissociation curve? (p50 value)?
Leftward (lowers p50)
How does lower pH shift the oxygen dissociation curve?
Rightward (lower p50)
How is the Bohr effect reflected in the Hb saturation curve?
Shifts entire curve right with increases in CO2 or lower pH
What is the function of 2,3 BPG?
Decreases Hb affinity for Oxygen to facilitate oxygen delivery
When is 2,3 BPG produced? (3)
Chronic hypoxia
Anemia
High altitude
Why can HbF bind oxygen better than HbA?
Lower affinity to 2,3 BPG
What is the toxic effect of CO?
Binds Hb much, much more tightly than oxygen (250x)
How does CO binding change the curve of the Hb sat curve? (i.e. what happens to the amount of O2 content at each level of PO2?
Lowers max (lowers the oxygen content at every level of PO2)
Why are there no signs of hypoxemia in CO poisoning?
Because the blood is still red
What happens to the affinity of Hb to oxygen when one CO molecule binds? What is the effect on the tissues to this?
Increases affinity (less is delivered to the tissue)
Why is there no reaction mechanism to CO binding in the body?
PaO2 is normal
What percent of CO2 is held as carbonic acid?
70%
What percent of CO2 is dissolved in the blood?
7%
What percent of CO2 is held as carbamino-Hb?
23%
What is the Haldane effect?
A higher PO2 will lower the CO2 bound to Hb
i.e. downward shift in the CO2 dissociation curve
Where in the body is the Haldane effect most prominent? Why?
In the lungs d/t high pO2
This allows the blood to load more Co2 in the tissues, and unload more CO in the lungs
True or false: methemoglobin is found normally in the blood
True–in very small amounts
The equation for oxygen content of the blood is:
O2 content = O2 binding capacity × SaO2 + Dissolved O2.
How does anemia affect this?
Lowers O2 binding capacity because there is less Hb to bind to
The equation for oxygen delivery to the tissues is:
O2 delivery = Cardiac Output × O2 content = Cardiac Output × [Dissolved O2 + HbO2]
How does 3rd degree heart failure affect this?
Lowers Cardiac output
The equation for oxygen delivery to the tissues is:
O2 delivery = Cardiac Output × O2 content = Cardiac Output × [Dissolved O2 + HbO2]
How does anemia affect this?
Lowers O2 Hb
The equation for oxygen delivery to the tissues is:
O2 delivery = Cardiac Output × O2 content = Cardiac Output × [Dissolved O2 + HbO2]
How does CKD affect this?
Contributes to anemia, thus lowering Hb content
What would happen if the tissue Po2 rose above the 40 mm Hg level?
The amount of oxygen needed by the tissues would not be released from the
hemoglobin.
During heavy exercise, extra amounts
of O2 (as much as 20 times normal) must be delivered from the hemoglobin to the tissues. But
this can be achieved with little further decrease in tissue PO. Why? (2)
because of (1) the steep slope of the
dissociation curve: a very small fall in Po2 causes large amounts of extra oxygen to be released
from the hemoglobin and (2) the increase in tissue blood flow caused by the decreased PO2.
What is the acid Bohr effect?
An
increase in plasma pH (alkalosis) causes a
left shift in the O2-Hb dissociation curve (and vice versa)
What is the CO2 Bohr effect?
Binding of CO2 to
Hb reduces the pH and the affinity of Hb
for O2.
What happens to [2,3 BPG] in stored blood? When could this be an issue?
Decreases
May be an issue in pts who are transfused a large amount of blood
How does the curve relating PO2 to [O2] of HbCO compare to that of anemia?
Same max, steeper curve
Where is CO2 bound in Hb?
The N terminus
CO2 binding to Hb favors the T or the R state?
T state
What are the three responses to high altitude?
- Increase erythropoietin
- Increase 2,3 BPG
- Increase renal excretion of HCO3
What are the three factors that can shift the oxygen-Hb dissociation curve to the right?
BAT ACE
BPG Altitude Temp Acid CO2 Exercise
What is the molecular basis for the sigmoidal shape of the Hb-oxygen dissociation curve?
Cooperative binding effect of oxygen
