Blood Gas Carriage

Question 1

Is oxygen soluble in water?

Answer 1

Not very

Question 2

How much dissolved oxygen does plasma contain at a partial pressure of 13.3kPa and a temperature of 37^oC?

Answer 2

0.13mmol/L

Question 3

How much oxygen do we need at rest?

Answer 3

12mmol per minute

Question 4

What volume of plasma would be required to meet the bodys oxygen requirements if the only source was dissolved oxygen?

Answer 4

92L

Question 5

What is the typical ppO₂ in the lungs?

Answer 5

13.3kPa

Question 6

What is the typical ppO₂ in the tissues?

Answer 6

~5kPa

Question 7

Draw an oxygen haemoglobin dissociation curve

Answer 7

Question 8

What does haemoglobin do?

With respect to oxygen binding

Answer 8

Reversibly binds to oxygen over a very narrow range of ppO₂

Question 9

Describe the structure of haemoglobin

Answer 9

Tetrameric protein, made up of 2 α and 2 ß subunits, with 4 haem groups

Question 10

What is the result of haemoglobin having 4 Haem groups?

Answer 10

It can bind to four molecules of oxygen

Question 11

What factors can decrease the affinity of Hb for O₂?

Answer 11

• H⁺
• Increasing temperature
• Increased CO₂

Question 12

What happens at sites of low pH and increased CO₂?

Answer 12

More oxygen is required and will be released

Question 13

What tissue may experience low pH and increased CO₂?

Answer 13

Muscle tissue during exercise

Question 14

What is the effect of low pH and increased CO₂ on haemoglobin dissociation called?

Answer 14

The Bohr effect

Question 15

What happens to the oxygen dissociation curve as a result of the Bohr effect?

Answer 15

It shifts to the right

Question 16

Draw a graph illustrating the effect of changing conditions on the oxygen dissociation curve

Answer 16

Question 17

What happens if the pO₂ in the capillaries falls?

Answer 17

pH falls and temperature falls, so Hb will give up more oxygen

Question 18

What is the result of a pO₂ fall in the capillaries on the saturation of Hb leaving the capillaries?

Answer 18

It is greatly reduced

Question 19

What can be used to calculated the percentage of oxygen that has been given up in a tissue if venous pO₂ is known?

Answer 19

A dissociation curve

Question 20

What happens to blood flowing through alveolar capillaries?

Answer 20

It picks up oxygen and looses carbon dioxide by diffusion of those gases across the alveolar wall

Question 21

What is the rate at which gases exchange determined by?

Answer 21

• Area available for exchange
• Resistance to diffusion
• Gradient of partial pressure

Question 22

What can be used to calculate the transfer factor of the lungs?

Answer 22

Carbon Monoxide

Question 23

What reactions can carbon dioxide undertake in the blood?

Answer 23

• Dissolves in water
• Reacts in water
• Binds directly to proteins

Question 24

How does the solubility of carbon dioxide compare to that of oxygen?

Answer 24

It is more soluble

Question 25

What does carbon dioxide form when it reacts with water?

Answer 25

H⁺ and HCO₃^-

Question 26

Is the reaction of carbon dioxide and water reversible?

Answer 26

Yes, depending on the concentration of reactants

Question 27

What is formed when carbon dioxide binds directly to proteins in the blood?

Answer 27

Carbamino compounds

Question 28

What is the Henderson-Hasselbach equation?

Answer 28

pH = 6.1 + Log( [HCO₃^-] / (pCO₂ x 0.23) )

Question 29

What happens to carbon dioxide in plasma?

Answer 29

It dissolves in plasma and undergoes a slow reaction with water, creating HCO₃^-

Question 30

Why does carbon dioxide undergo a slow reaction with water in plasma?

Answer 30

Because there is little carbonic anhydrase

Question 31

What happens to carbon dioxide in RBCs?

Answer 31

It reacts with water rapidly to form H⁺ and HCO₃^-

Question 32

Why does carbon dioxide react with water rapidly in RBCs?

Answer 32

Because carbonic anhydrase is present

Question 33

What happens to the H⁺ ions formed in carbon dioxides reaction with water in RBCs?

Answer 33

They bind to Hb

Question 34

What is the result of H⁺ ions binding to Hb?

Answer 34

It draws the reaction towards HCO₃^-

Question 35

What does the amount of HCO₃^- produced by carbon dioxide reacting with water in RBCs depend on?

Answer 35

Primarily, the buffering effects of Hb

Question 36

Why can Hb be said to act as a buffer?

Answer 36

H⁺ ions bind to Hb, so it acts as a buffer by ‘mopping up’ the ions

Question 37

What does the buffering action of Hb drive?

Answer 37

The reaction of carbon dioxide and water, and therefore the production of H⁺ and HCO₃^-

Question 38

What do carbamino compounds do?

Answer 38

Bind directly to proteins

Question 39

What does the binding of carbamino compounds to proteins contribute to?

Answer 39

Carbon dioxide transport

NOT acid base balance

Question 40

Are more carbamino compounds formed in arterial or venous blood?

Answer 40

Slightly more in venous blood

Question 41

Why are there slightly more carbamino compounds formed in venous blood?

Answer 41

Because pCO₂ is higher

Question 42

What is the normal carbon dioxide content of arterial blood?

Answer 42

21.5 mmol/L

Question 43

What is the normal carbon dioxide content of venous blood?

Answer 43

23.5 mmol/L

Question 44

How much carbon dioxide is transported from the tissues to the lungs?

Answer 44

2mmol/L

Question 45

How is the amount of carbon dioxide transported from the tissues to the lungs calculated?

Answer 45

Venous blood carbon dioxide - Arterial blood carbon dioxide

Question 46

In what forms does carbon dioxide travel from the tissues to the lungs?

Answer 46

• 80% travels as HCO₃^-
• 11% travels as carbamino compounds
• 8% travels as dissolved CO₂

Question 47

What does the amount of CO₂ that travels from the tissues to the lungs as HCO₃^- depend on?

Answer 47

How much O₂ has been lost, allowing it to bind to H^{<span>+</span>}