Oxygen and Carbon Dioxide Transport in the Blood – Flashcards

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question
In what 2 ways is oxygen transported in the blood?
answer
dissolved and bound to Hb
question
What percent of the total oxygen is dissolved in the blood?
answer
3%; for every mmHg of O2, the blood contains 0.003mL O2/100mL of blood
question
What form of oxygen is PaO2 a measure of?
answer
dissolved O2
question
What form of oxygen is PaO2 a measure of?
answer
dissolved O2
question
What is the importance of the dissolved O2?
answer
it drives the concentration gradient of O2 across the respiratory membrane
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What is a normal PaO2?
answer
100mmHg
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What is positive cooperativity?
answer
the binding of each successive molecule of O2 induces a conformational change in the Hb and making it easier for the next molecule to bind
question
Approximately how much of the RBCs is Hb?
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1/3; if a PCV = 45, the Hb = 15g/dL
question
What is the shape of the oxyhemoglobin dissociation curve?
answer
sigmoidal
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What is oxyhemoglobin?
answer
Hb bound to O2
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What is reduced Hb?
answer
unbound Hb
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At what PO2 is Hb 97% saturated? 75% saturated? 50% saturated?
answer
100mmHg; 40mmHg; 28mmHg
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Where is Hb normally 97% saturated?
answer
arterial blood
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Where is Hb normally 75% saturated?
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venous blood
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What will PO2 be if SpO2 is 85%?
answer
estimate! between 40 and 100 (75% and 97% SpO2) so probably about 70mmHg
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Approximately how much O2 can a normal gram of Hb carry?
answer
1.34mL
question
What is the Oxygen Concentration equation?
answer
CaO2 = (1.34 x Hb x (%sat/100)) + (0.003 x PO2) where:
CaO2 = concentration of oxygen in mL/dL
Hb = hemoglobin concentration in g/dL
PO2 = partial pressure of O2 in blood in mmHg
question
Which part of the oxygen concentration equation denotes the O2 bound to Hb? Which part denotes the dissolved O2?
answer
(1.34 x Hb x (%sat/100)); (0.003 x PO2)
question
What will anemia do to Hb concentration?
answer
decrease it
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What will polycythemia do to Hb concentration?
answer
increase it
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What does an SpO2 <95% denote?
answer
hypoxemia
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What 5 things causes a shift to the right of the O2 Hb dissociation curve?
answer
1) decrease in pH
2) increase in temp
3) increase in RBC 2,3 DPG
4) increase in H+
5) increase in CO2
question
What is the Bohr Effect?
answer
a decrease in Hbs affinity for O2; a shift to the right of the O2 Hb dissociation curve
question
What does the Bohr effect do to a patients P50 value?
answer
increases it
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How does the Bohr Effect effect tissue offloading?
answer
it increases it
question
What 5 things cause a shift to the left of the O2 Hb dissociation curve?
answer
1) increase in pH
2) decrease in temp
3) decrease in RBC 2,3 DPG
4) decrease in H+
5) decrease in CO2
question
What is 2,3 DPG?
answer
glycolysis intermediate
question
What does a left shift of the O2 Hb dissociation curve indicate? How does this effect tissue offloading?
answer
it indicates an increase in Hbs affinity for O2; this decreases offloading at the tissues
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What does a left shift do to a patients P50 value?
answer
decreases it
question
What is carboxyhemoglobin?
answer
carbon monoxide bound to hemoglobin
question
Why is CO so toxic?
answer
Hbs affinity for CO is 240x greater than its affinity for O2, therefore with a CO partial pressure of only 0.16mmHg 75% of Hb is bound to CO
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Which way does CO toxicity shift the O2 Hb dissociation curve?
answer
left which means that there isnt much offloading at the tissues
question
What is a non-invasive way to measure oxygenation? When is this method not recommended?
answer
pulse oximetry; it cant distinguish between oxyhemoglobin and carboxyhemoglobin, and therefore is not recommended for CO toxicity patients
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What are the 5 main causes of hypoxemia?
answer
1) decreased inspired O2 partial pressure
2) hypoventilation
3) V/Q mismatch
4) right to left shunts
5) diffusion impairment
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True or False: A left to right anatomic shunt will cause hypoxemia.
answer
False! A right to left shunt will!
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In what 3 ways is CO2 transported in the blood?
answer
1) dissolved (10%)
2) carbamino compounds (30%)
3) bicarbonate (60%)
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What is carbaminohemoglobin?
answer
CO2 bound to Hb
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Hb will more readily bind CO2 than O2. How is this helpful?
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the unloading of O2 at the tissues supports the binding of CO2 and the unloading of CO2 at the respiratory membrane (via diffusion gradient) supports the binding of O2
question
How is bicarbonate formed?
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CO2 + H2O ;-CA-; H2CO3 ;/*> H+ + HCO3-
*/ where CA = carbonic anhydrase
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Where is CA found?
answer
in the RBCs, not the plasma
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What is the chloride shift?
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When bicarb is made, the bicarb ion diffuses out of the cell, but H+ remains in the cell, so Cl- diffuses in to maintain electrical neutrality
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How does bicarbonate benefit the plasma?
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it acts as a buffer
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Why is it important that the bicarbonate equation is reversible?
answer
at the level of the respiratory membrane so CO2 can form and diffuse across the membrane into the alveoli
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What is bicarbonate a marker of?
answer
metabolic function in acid-base balance
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What is the Haldane effect?
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deoxygenation of the blood increases its ability to carry carbon dioxide and oxygenated blood has a reduced capacity for carbon dioxide; this doubles the amount of CO2 picked up at the tissues and doubles the CO2 released at the lungs
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What is respiratory acidosis and what is it a consequence of?
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blood pH ;7.4 and pCO2 ;40mmHg; hypoventilation
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What does hypoventilation do to the carbonic acid equation?
answer
pushes it towards the left producing more HCO3- and H+
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How does the body compensate for chronic respiratory acidosis?
answer
the kidneys preserve more HCO3- and excrete more H+
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In what 2 instances might you see respiratory acidosis?
answer
anesthesia and brain stem injuries
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What is respiratory alkalosis and what is it a consequence of?
answer
blood pH ;7.4 and pCO2 ;40mmHg; hyperventilation
question
How does the body compensate for chronic respiratory alkalosis?
answer
the kidneys preserve more H+ and excrete more HCO3-
question
What can respiratory alkalosis occur secondary to?
answer
pain or hypoxemia
question
Which of the following is the major transport form of CO2 in the blood?
a) Bicarbonate
b) CO2 is not transported in the lungs
c) Bound to Hb
d) dissolved
answer
a
question
Which of the following best describes the Bohr effect?
a) Deceased P50
b) Increased O2 offloading at the tissues
c) Left shift in the oxyhemoglobin dissociation curve
d) Increased Hb affinity for O2
answer
b
question
Which of the following is false regarding the consequences of exposure to carbon monoxide?
a) Left shift of the oxyHb dissociation curve
b) Decreased CaO2
c) Decreased Hb affinity for O2
d) Decreased offloading of O2 at the peripheral tissues
answer
c
question
Which of the following best describes a respiratory acidosis?
a) PCO2 = 40mmHg; pH = 7.4
b) PCO2 = 60mmHg; pH = 7.4
c) PCO2 = 60mmHg; pH = 7.3
d) PCO2 = 40mmHg; pH = 7.3
answer
c
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