Respiratory Physiology Lecture 6 Part 28: Carbon Dioxide and Hydrogen Ion Transport

Question 1

How is CO₂ carried in the blood?

Answer 1

• Dissolved (5%)
• Bicarbonate (HCO3^- → 60-65%)
• Carbamino compounds (ex. Hb → 25-30%)

Question 2

CO₂ solubility in blood

Answer 2

Question 3

What forms of CO₂ transport occur in the blood?

Answer 3

• Bicarbonate
• Carbamino compounds

Question 4

How is CO₂ carried in bicarbonate?

Answer 4

reacts with water to form carbonic acid which then dissociates to hydrogen ions and bicarbonate

Question 5

What does the formation of bicarbonate occur in RBC and not plasma?

Answer 5

Reaction would be much slower in the plasma since the RBC has the enzyme carbonic anhydrase (CA) to catalyze the reaction in the RBC

Question 6

How does bicarbonate developed in the RBC move into the plasma?

Answer 6

• Cell membranes are typically impermeable to charged ions such as the bicarbonate and chloride but RBC can exchange bicarbonate for chloride using the anion exchange protein. So the rise in bicarbonate leads to bicarbonate export and chloride import.

Question 7

Why does Chloride come into the RBC when bicarbonate leaves?

Answer 7

Having chloride come into RBC maintains electrical neutrality of RBCs

Question 8

What do H⁺ atoms produced from carbonic acid dissociation do?

Answer 8

To maintain electrical neutrality and allow for HCO₃^- to exit the cells, H+ will increase in venous blood (And therefore ↓ pH)

Question 9

How does CO₂ form carboamino compounds?

Answer 9

Combination of CO₂ with amino group in blood proteins (Globins in Hb)

• no enzyme required

Question 10

Why does CO₂ attached to Hb?

Answer 10

DeoxyHb has much higher affinity for CO₂ compared to OxyHb

• CO₂ will help to unload O₂ from Hb in peripheral tissue

Question 11

Carbon dioxide movement in the peripheral tissue

Answer 11

CO₂ produced in the peripheral cells, exits cells, is dissolved in interstitial fluid, and diffuses to blood. Here CO₂:

• remains in plasma as dissolved CO₂ (P_CO2)
• enters RBC and remains dissolved as CO₂, is bound to DeoxyHB or reacts with water to produce HCO₃^- and H+ (HCO₃^- will then exit RBC; H+ will interact with Hb)

Question 12

Carbon dioxide movement at the level of the respiratory membrane

Answer 12

Dissolved CO₂ in blood diffuses into alveoli. Lower P_CO2 in plasma recalls dissolved C_O2 from RBC and changes equilibrium for CO₂/H₂O reactions (bicarbonate) and CO2/Hb reactions (carboamino). More deoxyHb will then be available to bind with O₂ again.

Question 13

What causes CO₂ to move from vessels to alveoli?

Answer 13

P_CO2 at the level of the respiratory membrane

Before diffusion P_CO2ALV << P_CO2BLOOD which causes the CO₂ to diffuse across the membrane

Question 14

Where is Hydrogen produced with gas exchange?

Answer 14

H+ is produced during HCO₃^- formation in RBC

Question 15

What happens to Hb once it is produced?

Answer 15

DeoxyHb has much higher affinity for H+ compared to OxyHb so a large proportion of H+ is bound to Hb and not dissolved in RBC or plasma

Question 16

What does Hb bound to H+ cause?

Answer 16

Favours the unloading of oxygen from Hb at level of peripheral tissues

Question 17

Why is it important the H+ bind to Hb?

Answer 17

Physiological pH (7.4) in blood is preserved and venous blood is only slightly more acidic (7.3) than arterial pH

• Otherwise too much H+ will dissolve and increase pH more substantially at level of the venous blood

Question 18

What is the key role of Hb binding with H+?

Answer 18

Hb has a key role in buffering the production of H+ in the peripheral tissues and capillaries

Question 19

Hb-H+ in the lungs

Answer 19

In the lungs, this equilibrium is reversed and H+ interacts with HCO₃^- and Hb is available for binding with O₂

• In the lungs the deoxyHb releases the H+ i which react with bicarbonate to form carbonic acid which dissociates to form water and carbon dioxide under influence of carbon anhydrous and so more deoxyHb is available to pick up O₂ again

Question 20

Conditions for the imbalance between CO₂ production and CO₂ elimination through ventilation

Answer 20

Respiratory acidosis, alkalosis

Question 21

Respiratory acidosis

Answer 21

Hypoventilation (CO2 production > CO2 elimination): not only PCO2 ↑ but also H+ concentration ↑ so lower pH

Question 22

Respiratory alkalosis → hyperventilation (CO2 production < CO2 elimination): not only PCO2 ↓ but also H+ concentration ↓

Answer 22

Hyperventilation (CO2 production < CO2 elimination): not only PCO2 ↓ but also H+ concentration ↓ so increase in pH

Question 23

Effects of exercise on metabolism

Answer 23

Metabolic acidosis/ alkalosis

Question 24

Metabolic acidosis

Answer 24

↑ in blood H+ concentration independent from changes in P_CO2

Question 25

Metabolic alkalosis

Answer 25

↓ in blood H+ concentration independent from changes in PCO2