Topic 13: Respiratory System - CO2 Transport

Question 1

Which 3 ways is CO2 carried?

Answer 1

1) dissolved in plasma (8%)
2) Bound to hemoglobin = carbamino Hb (CO2 on globin) = 20%
3) As bicarbonate ions (HCO3-) = 72%

Question 2

What 2 ways is CO2 dissolved in plasma?

Answer 2

1) At the lungs (external resp)
2) At the tissues (internal resp)

Question 3

What are the pressures in the lungs when CO2 is carried? (3)

Answer 3

Alveolar PCO2 = 40 mHg
Resting arterial PCO2 = 45 mmHg
Venous PCO2 = 40 mmHg

Question 4

which direction does CO2 diffuse in the lungs in plasma?

Answer 4

capillary to alveolus

Question 5

What are the pressures at the tissue when CO2 is carried? (4)

Answer 5

Arterial PCO2 = 40 mmHg
ICF PCO2 => 45 mmHg
ISF PCO2 = 45 mmHg
Resting Venous PCO2 = 45 mmHg

Question 6

Which direction does CO2 diffuse at the tissues in plasma? (3)

Answer 6

cell to ISF to capillary

Question 7

How is CO2 carried when bound to Hb? (2)

Answer 7

• CO2 binds to deoxyHb better than to oxyHb
• therefore Hb binds CO2 readily at the tissues

Question 8

Which 2 ways is CO2 carried a bicarbonate ions? (2)

Answer 8

1) Inside RBC at tissues (increase CO2)
2) Inside RBC at lungs

Question 9

How is CO2 transported inside RBC at tissues? (3)

Answer 9

• HCO3- transported out of RBC in exchange for Cl- = chloride shift
• this allows more HCO3- to be made
• therefore venous blood RBC have more CL-

Question 10

bicarbonate ions inside RBC at tissue reactions

Answer 10

Question 11

What is the first reaction occuring inside RBC at the lungs? (3)

Answer 11

1) O2 + deoxyHb -> HbO2
- note that deoxyHb = HbH and/or HbCO2
- HbO2 binds CO2 + H+ poorly, so CO2 is released (Haldane effect) and H+ released

Question 12

What is the second reaction occurring inside RBC at lungs? (4)

Answer 12

H+ + HCO3- -> H2CO3 -> CO2 + H2O
- therefore decreases HCO3- IN RBC, then HCO3- moves into RBC (down gradient)
- exchanges for Cl- (reverse chloride effect)
- note that CO@ moves from rbc -> plasma -> alveolar air -> out