Exam #3: Transport of Oxygen & Carbon Dioxide

Question 1

What is the difference between dissolved oxygen & conjugated oxygen?

Answer 1

Dissolved= Only dissolved gas generates partial pressure
(0.3%)

Conjugated= conjugated to Hb
(99.7% –reserve to draw from/ buffer)

Question 2

Describe the structure of HbA.

Answer 2

2x alpha chains
2x Beta chains
4x Heme groups that can bind 1 O2

Thus HbA can bind 4 O2 molecules

Question 3

Describe the structure of heme.

Answer 3

A prophyrin ring

Fe++ reversible binds O2

Question 4

What is methemoglobin?

Answer 4

Fe+++ instead of Fe++ heme

DOES NOT bind O2

Question 5

What causes an increase in methemoglobin?

Answer 5

1) Oxidation of Fe++ to Fe+++ by nitrites & sulfonamides

2) Deficiency is methemoglobin reductase

Question 6

Describe the structure and function of Fetal Hb.

Answer 6

2x Beta chains are replaced by gamma chains

Higher affinity for O2 than HbA facilitates oxygen movement to the fetus

Question 7

What is Hemoglobin S?

Answer 7

• Cause of sickle cell disease
• Abnormal beta subunits
• Forms sickle- shaped rods in RBCs that occlude small blood vessels
• Lower affinity for oxygen

Question 8

What is the oxygen binding capacity?

Answer 8

The maximum oxygen volume that can combine with Hb, which is dependent on

• Hb concentration
• binding properties

Question 9

What is the oxygen content? What is the equation for oxygen content?

Answer 9

Actual amount of O2 per volume of blood

O2 binding capacity x SaO2 + Dissolved O2

Question 10

How is oxygen content altered in anemia?

Answer 10

Decreased Hb decreases oxygen content

Question 11

What factors determine oxygen delivery to the tissues?

Answer 11

Cardiac ouput
Oxygen Content

= CO x Oxygen content

Question 12

Draw the oxygen dissociation curve.

Answer 12

Hb saturation % vs. partial pressure of oxygen

Question 13

What are the important features of the oxygen dissociation curve?

Answer 13

• 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

Question 14

What is the P50 value?

Answer 14

PO2 at which Hb is 50% saturated

Question 15

What happens when the P50 is larger?

Answer 15

Shift the oxygen dissociation to the right

• Weaker binding
• Hb releases O2 eaeier

Question 16

What happens when the P50 is smaller?

Answer 16

Shift the oxygen dissociation to the left

• Tighter binding
• Hb release O2 harder

Question 17

How does an increase in temperature shift the oxygen dissociation curve?

Answer 17

Shift to the right

Easy delivery of oxygen

Question 18

How does hypothermia change the oxygen dissociation curve?

Answer 18

Left shift

Preserve oxygen

Question 19

How does a decreased in pH shift the oxygen dissociation curve? Give some examples. What is this called?

Answer 19

Right shift

• Acidosis
• DKA
• CKD

“Acid Bohr effect”

Question 20

How does an increase in pH shift the oxygen dissociation curve?

Answer 20

Left shift

Question 21

What is the Co2 Bohr effect? How does high CO2 affect the oxygen dissociation curve?

Answer 21

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

Question 22

What is 2,3-diphosphoglycerate (2,3-BPG)? How does it affect the oxygen dissociation curve & when is it increased?

Answer 22

End product of RBC metabolism that is increased in:

• Hypoxia
• High altitude
• Anemia

Increased= right shift

Question 23

How is the 2,3-BPG concentration altered in stored blood? What is the impact?

Answer 23

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

Question 24

Describe the toxic effects of CO.

Answer 24

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

Question 25

What are the symptoms of CO intoxication?

Answer 25

Altered reaction time
Blurred vision
Unconsciousness

Question 26

List the three forms of CO2 in the blood and their relative concentrations.

Answer 26

1) 7% is dissolved CO2
2) 23% is conjugated to Hb
3) 70% is HCO3-

Thus, HCO3- (bicarbonate) is the main form of CO2 in the blood

Question 27

What reaction is catalyzed by carbonic anhydrase?

Answer 27

Carbon dioxide and water to bicarbonate and protons

Question 28

Draw the CO2 binding curve.

Answer 28

N/A

Question 29

What is the Haldane effect?

Answer 29

Effect of oxygen on the CO2 equilibrium

• Higher PO2 will shift the CO2 equilibrium to the right
• Allows the blood to load more CO2 in the tissue and unload more at the lungs