Carbon Dioxide Transport + Role In pH Balance

Question 1

Why is a very low blood pH a cause of coma?

Answer 1

• phosphofructokinase is pH dependent > activity decreases with decreasing pH
• glucose utilisation in brain cells is impaired

Question 2

What are clinical consequences of decreases blood pH?

Answer 2

Drowsiness
Stupor - near unconsciousness
Coma

Question 3

What is the blood pH range?

Answer 3

7.35-7.45

Question 4

How can CO2 form H+ and bicarbonate ions?i

Answer 4

CO2 + H2O <-> H2CO3 <-> H+ + HCO3-

• reacts with water to form carbonic acid
• carbonic acid dissociates into H+ and HCO3-

Question 5

Ratio between CO2 and HCO3- in order to maintain normal body pH

Answer 5

CO2 : HCO3-
1 : 20

Question 6

Why must we have methods of transport of CO2 in blood?

Answer 6

• To prevent drop in pH
• 1:20 ratio of CO2:HCO3 needed to maintain normal body pH
• 1 CO2 only produces 1 HCO3-
• blood pH will become more acidic i due to excess H+ ions without alternate transport

Question 7

What are the methods of transport of CO2 in blood?

Answer 7

Carb amino compounds
As bicarbonate
Dissolved in plasma

Question 8

How do we form carbamino compounds?

Answer 8

CO2 binds to haemoglobin (to amine groups)

Question 9

Function of carbamino compounds

Answer 9

• stabilising pH
• stabilises T state of haemoglobin > promotes release of O2 into respiring tissues

Question 10

What happens to carbamino compounds at the lungs?

Answer 10

• CO2 given up by haemoglobin
• Hb becomes O2 rich
• CO2 expired
  Haldane effect

Question 11

How much CO2 is transported as bicarbonate ions in RBCs?

Answer 11

60%

Question 12

What enzyme converts CO2 to bicarbonate ions in RBCs?

Answer 12

Carbonic anhydrase

Question 13

How is excess HCO3- transported back into the blood?

Answer 13

Via chloride-bicarbonate exchanger
Act as a buffer to H+ in blood plasma.

Question 14

What is haemoglobin role in H+ buffering?

Answer 14

• less O2 bound to Hb > T state > more H+ ions bind
• more O2 bound to Hb > R state > less H+ ions bind

Question 15

How does bicarbonate buffer extra acid?

Answer 15

H+ + HCO3- > CO2 + H2O
- CO2 levels increase > removed by breathing
- More HCO3 must be produced to replenish buffers

Question 16

What is the role of the kidneys and the lungs in blood pH?

Answer 16

• lungs: how much CO2 is present > change rate/depth of breathing | faster response
• kidneys: how much HCO3- is present | slower response

Question 17

What is HCO3- conc. controlled by?

Answer 17

Kidneys

Question 18

How much CO2 is transported in plasma?

Answer 18

10%

Question 19

How much CO2 is transported as carbamino compounds?

Answer 19

30%

Question 20

Relationship between pCO2 and pH

Answer 20

inversely proportional
if pCO2 falls > pH rises
if pCO2rises > pH falls

Question 21

Why is the reaction of CO2 to carbonate ions faster in RCBs than plasma?

Answer 21

Carbonic anhydrase in RBCs
Enzyme increases speed of reaction

Question 22

How is the majority of CO2 transported?

Answer 22

As bicarbonate ions

Question 23

Define respiratory acidosis

Answer 23

Failure of ventilation leading to accumulation of CO2 causing a decrease in pH

Question 24

Define respiratory alkalosis

Answer 24

Hyperventilation causes low levels of CO2 resulting in an increase in pH

Question 25

Steps in interpreting arterial blood gas

Answer 25

• look at pH: normal/acidosis/alkalosis
• look at pCO2: respiratory
• look at HCO3-: metabolic
• look at HCO3- again: check for compensation
• look at pCO2 again: check for compensation

Question 26

What does the pCO2 result in a ABG tell you?

Answer 26

Where it’s respiratory or not
High pCO2 > acidifying effect
Low pCO2 > alkalising effect

Question 27

What does the bicarbonate result tell you in an ABG?

Answer 27

Where its metabolic or no t
Low HCO3- > acidosis
High HCO3- alkalosis

Question 28

Difference between hypoxia + hypoxemia

Answer 28

• hypoxaemia: decreased pO2 in blood
• hypoxia: decreased level of O2 in tissues