CO2 Transport in Blood

Question 1

What is the partial pressure of CO2 at complete equilibrium?

Answer 1

40mmHg

Question 2

What 3 places are respiratory membranes found?

Answer 2

Respiratory bronchioles
Alveolar ducts
Alveoli

Question 3

What 4 factors affect rate of Gas diffusion?

Answer 3

Thickness of membrane
Diffusion coefficient of gas through membrane
Surface area of membrane
∆P (gas) between 2 sides of membrane

Question 4

What is the diffusion coefficient?

Answer 4

Measure of how easily a gas diffuses through liquid or tissue

Question 5

What two things is the diffusion coefficient dependent on?

Answer 5

Solubility of gas
Size of gas molecule

Question 6

What happens to O2 and CO2 transport if membrane is damaged by disease?

Answer 6

O2 transport reduced substantially causing death before CO2 diffusion is reduced

Question 7

What is the total surface area of respiratory membranes?

Answer 7

70m^2

Question 8

What 2 diseases reduce surface area?

Answer 8

Emphysema
Lung cancer

Question 9

What is the effect of partial pressure difference?

Answer 9

When 1 side is greater than the other, the diffusion occurs from higher to lower

Question 10

What 2 factors affect difference in P (gas)?

Answer 10

Increasing ventilation increases differences
Inadequate ventilation reduces differences

Question 11

What 3 forms is CO2 transported in?

Answer 11

Dissolved CO2
with proteins as carbamino compounds (Hb)
HCO3-

Question 12

Why does the majority of H+ combine with Hb?

Answer 12

Reduced Hb is less acidic so better proton acceptor

Question 13

What does the shift of chloride ions into RBCs cause?

Answer 13

Buffering of hydrogen ions onto reduced hemoglobin increases intercellular osmolarity -> water enters cell leading to an increase in mean corpuscular volume

Question 14

What does blood carry more of?

Answer 14

Carries 24x more CO2 than O2

Question 15

What is 10% of excreted lung CO2 carried as?

Answer 15

In mixed venous blood in dissolved form from the tissues

Question 16

Where is carbonic anhydrases found?

Answer 16

Endothelium of pulmonary circulation

Question 17

What does CA catalyse?

Answer 17

CO2 + H20 -> H2CO3

Question 18

When is the dissociation of H2CO3 rapid?

Answer 18

Absence of the enzyme

Question 19

What is 60% of excreted lung CO2 carried as?

Answer 19

In mixed venous blood as HCO3-

Question 20

Describe the chloride shift.

Answer 20

HCO3- diffuses out of RBC
H+ trapped in RBC (membrane impermeable to H+)
Cl- ions driven into RBC by potential gradient to maintain neutrality
RBC swell

Question 21

What happens as blow flows through tissue?

Answer 21

Loses O2 (deoxyhemoglobin)
Gains CO2 (generates bicarbonate and H+)

Question 22

Describe the Haldane effect?

Answer 22

Deoxyhaemoglobin has a higher affinity for H+ than oxyhaemoglobin
H+ + HbO2 -> HbH+ + O2 = prevents H+ leaving cell and prevents pH dropping

Question 23

What 2 things does the amount of CO2 bound as carbamate to Hb or plasma proteins depend on?

Answer 23

O2 Sat of Hb
H+ conc

Question 24

What % is CO2 carried in carbamino form?

Answer 24

30%