4. Blood Gas Carriage

Question 1

What is the plasma content of dissolved oxygen at partial pressure 13.3kPa and at a temperature of 37C?

Answer 1

0.13mmol/L.

Question 2

How much oxygen do we need per minute at rest?

Answer 2

12mmol.

Question 3

How many litres of blood would be needed for the 12mmol demand at rest if oxygen was only dissolved in the blood?

Answer 3

92 litres.

Question 4

What is the typical ppO2 in the lungs?

Answer 4

13.3kPa.

Question 5

What is the typical ppO2 in the tissues?

Answer 5

5kPa.

Question 6

What is the shape of an oxygen-haemoglobin dissociation curve?

Answer 6

Sigmoidal curve.

Question 7

What is the structure of haemoglobin?

Answer 7

A tetrameric protein with 2 alpha and 2 beta subunits.

Question 8

How many molecules of oxygen can haemoglobin bind to?

Answer 8

Four molecules.

Question 9

What are the two states of haemoglobin?

Answer 9

Low affinity T state, and high affinity R state.

Question 10

What happens to Hb state when O2 binds?

Answer 10

More R state which promotes more O2 binding.

Question 11

What decreases affinity of Hb for O2?

Answer 11

H+, increasing temperature and CO2.

Question 12

What is the Bohr effect?

Answer 12

Where there is low pH, in metabolically active tissue for example, more oxygen is required so the oxygen dissociation curve shifts right and O2 is more readily given off.

Question 13

How can the amount of oxygen given to a tissue be calculated?

Answer 13

If venous pO2 is know, the dissociation curve can calculate it.

Question 14

What affects the rate of gas exchange?

Answer 14

Area available for the exchange, resistance to diffusion, gradient of partial pressure.

Question 15

How can transfer factor be calculated?

Answer 15

With carbon monoxide.

Question 16

How does CO2 react in the blood?

Answer 16

It dissolves in water, or reacts with water, and binds directly to proteins.

Question 17

How does solubility in water differ between CO2 and O2?

Answer 17

CO2 is more soluble in water than O2.

Question 18

How does CO2 react with water in blood?

Answer 18

It forms H+ and HCO3-. This is a reversibly reaction.

Question 19

What does CO2 form when it binds directly to proteins?

Answer 19

Carbamino compounds.

Question 20

What is the Henderson-Hasselbach equation?

Answer 20

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

Question 21

What is the slow reaction of CO2 in plasma?

Answer 21

With water to create HCO3-.

Question 22

Why is the reaction of CO2 and water slow in the plasma?

Answer 22

Little carbonic anhydrase to catalyse it.

Question 23

How does CO2 react with water in red blood cells?

Answer 23

Rapidly to form H+ and HCO3-.

Question 24

What does the amount of HCO3- made by CO2 in RBCs depend on?

Answer 24

The buffering effects of Hb.

Question 25

How does Hb act as a buffer for H+?

Answer 25

H+ binds to it so Hb acts as a buffer mopping up H+ ions. This drives the reaction of CO2 with water to make more H+ and HCO3-.

Question 26

Why are more carbamino compounds formed in the venous blood?

Answer 26

The pCO2 is higher.

Question 27

What is the normal arterial blood concentration of CO2?

Answer 27

21.5mmol/litre.

Question 28

What is the normal venous blood concentration of CO2?

Answer 28

23.5mmol/litre.

Question 29

How does CO2 travel?

Answer 29

As HCO3-, as carbamino compounds, as dissolved CO2.