Resp S4 - Gases In The Blood

Question 0

What causes the oxygen dissociation curve to shift to the left?

Answer 0

Increased pH
Decreased BPG
Decreased temperature

Question 1

What causes the oxygen dissociation curve to shift to the right?

Answer 1

Decreased pH
Increased BPG
Increased temperature

Question 2

How may diffusion be measured?

Answer 2

The carbon monoxide transfer factor (TLCO)

Question 3

Describe the TLCO test

Answer 3

Aka CO transfer factor
The subject takes a single vital capacity breath of a gas mixture containing air, 14% helium and 0.1% CO
The first 750ml exhaled is discarded and the next litre is collected
The amount of CO transferred from alveoli to blood is an estimate of the diffusion capacity of the lung

Question 4

In the TLCO test, what is the purpose of the 14% helium?

Answer 4

To allow for correction of the diluting effects of the residual volume

Question 5

In the TLCO test, what is the purpose of the 0.1% CO?

Answer 5

Haem has a very high affinity for CO
Almost all the CO entering the blood binds to Hb
So plasma CO is taken to be nought

Question 6

Why is plasma [CO2] so much higher (~3* [O]2) than might be expected of a waste product?

Answer 6

CO2 is also used as part of pH control

Question 7

How is CO2 transported in the blood?

Answer 7

80% as HCO3-
11% as carbamino compounds
8% as dissolved CO2

Question 8

How is CO2 converted to HCO3-?

Answer 8

CO2 + H2O H+ + HCO3-

This is a highly reversible reaction

Question 9

How is plasma [HCO3] so much higher than [CO2] if they’re in equilibrium?

Answer 9

In RBCs, the H+ produced from the reaction binds to haemoglobin, whilst the HCO3 leaves the cell by a transmembrane Cl antiporter.
This pulls the reaction forward, meaning there’s a higher plasma [HCO3] than [CO2].
The kidney has a huge regulatory role in control of HCO3 production and excretion

Question 10

So how is blood pH controlled?

Answer 10

A balance between the rate of breathing in the lungs and processes in the kidney

Question 11

What’s the CO2 difference between arterial and venous blood?

Answer 11

In venous blood there is more CO2 as a result of extra acids found in the tissues
There is also more HCO3 as the buffering reaction occurs with the result of stabilising pH

Question 12

What happens in the lungs in terms of pH and carbon?

Answer 12

Haemoglobin releases the H+ bound to it to pick up more oxygen
The H+ then reacts with HCO3 to form CO2, which is then breathed out
The pH therefore remains stable throughout