Blood gases

Question 1

How do partial pressures relate to the amount of gas transport?

Answer 1

The partial pressure is the concentration gradient for the gases to diffuse down

Question 2

How can gas be transported?

Answer 2

Gas is dissolved in solution

Gas can bind to carrier molecules (proteins) to be transported

Question 3

What are the determinants of how much gas is transported?

Answer 3

How much gas is contained in a litre of blood

How much blood is transported

Modulation of gas content in blood

Question 4

What is the equation for the amount of gas dissolved?

Answer 4

Amount dissolved = partial pressure x Solubility coefficient (alpha)

Amount of gas dissolved is proportional to its partial pressure

Question 5

What is the normal alveolar partial pressure of oxygen and carbon dioxide?

Answer 5

O2 = 13 kPa
CO2 = 5kPa

Question 6

For every litre of blood how much 02 is dissolved?

Answer 6

About 2.9 ml/L is dissolved from a PO2 of 13kPa

Alternatively we have a lot of CO2 (~ 25ml/L

Question 7

What are the gas carrier molecules?

Answer 7

Haemoglobin 4 Haem +globin chains)

Question 8

Why is haemoglobin packaged into RBCs?

Answer 8

Haemoglobin MW = 64.5KDa and therefore is small enough to be excreted through the glomerulus.
To prevent this it is packaged into RBCs to ensure that it is not excreted.

Question 9

What will the globin chains bind to?

Answer 9

alpha and beta chains will bind to CO2 and H+ ions

Question 10

What will the Haem groups bind to/carry?

Answer 10

Each moiety will bind to an O2 molecule

Question 11

What are the main roles of Haemoglobin?

Answer 11

Carries O2 (haem groups), CO2 (globin chains) and buffers pH

Question 12

If there is a higher concentration of O2 in the RBCs then what will happen to the O2?

Answer 12

More O2 in plasma will diffuse into the RBC and therefore this will shift eqm to produce more oxyhaemoglobin.

Question 13

What is the relationship between the alveolar, arterial pressure and Hb saturation?

Answer 13

Alveolar pressure sets the arterial pressure and therefore will be equal.
The O2 molecules in plasma will also diffuse into RBCs and equilibrate with cytoplasm.

Question 14

How do you calculate the % saturation of Hb?

Answer 14

O2 bound / O2 capacity x100

Question 15

What is the physiological significance of the haemoglobin saturation curve?

Answer 15

When one O2 molecule binds to Hb, it becomes easier for a second O2 molecule to bind to another site of Hb since there is a shape change in the protein structure.
This leads to a quick increase in saturation over a shorter PO2.
The curve then plateaus as the 4th O2 molecule binds

Question 16

What is the P50?

Answer 16

The partial pressure required for 50% saturation.

If P50 is further to the left then there is a higher affinity for O2.

Question 17

Why is it important for the alveolar gases to have a high P02?

Answer 17

This means that the % saturation of Hb is at 100% even when there are slight changes in PO2.
eg. even at a PO2 of 9, the %saturation is still around 100%

Question 18

What is the difference in sensitivity of Partial pressure changes in the lungs and tissues?

Answer 18

Lungs (loading) - low sensitivity of PO2 changes

Tissues - High sensitivity of PO2 changes

Question 19

What is the Bohr effect?

Answer 19

Hb affinity for O2 decreases (P50 increases) and the curve shifts to the right when there is increased:
CO2, H+, 2-3DPG, higher temperature.

Question 20

What is the significance of the bohr effect?

Answer 20

Enables us to have local matching of O2 delivery to tissue metabolic needs.

Question 21

What is 2-3-DPG?

Answer 21

Formed as a side reaction of glycolysis from anaerobic respiration in RBCs.

Question 22

What does 2-3-DPG bind to?

Answer 22

Binds to the Beta chains of Hb

Binds more favourably to deoxyHb than OxyHb

Question 23

Why is 2-3-DPG useful?

Answer 23

In cases such as chronic Hypoxia and blood alkalosis where Hb curve shifts to the left, then increasing 2-3-DPG counteracts the left shift (bringing it back right) to help maintain O2 delivery to tissues.

Question 24

What happens if we decrease 2-3-DPG levels?

Answer 24

Decreases O2 availability in transfused blood

Question 25

What is a haematocrit?

Answer 25

Measure of the red cell volume

Question 26

What is O2 capacity?

Answer 26

The capacity of Hb to bind to O2 (if 100% saturated)

Question 27

What is the normal amount of O2 bound to Haemoglobin?

Answer 27

195 - 200 ml/L

Question 28

What is the normal amount of O2 dissolved in the blood?

Answer 28

about 3 ml/L

Question 29

What is the relationship between O2 content and O2 consumption?

Answer 29

The rate at which oxygen is consumed by the periphery is equal to the difference between the oxygen content in arterial blood leaving the heart and in the mixed venous blood returning to the heart

VO2 = (CaO2 - CvO2 ) x CO

Question 30

What enzyme speeds up formation of H2CO3?

Answer 30

Carbonic anhydrase

Question 31

What is the main way CO2 is carried in the body?

Answer 31

65% as bicarbonate in the plasma

20% as bicarbonate in the RBCs

Question 32

What is the main store of CO2 in the body?

Answer 32

As Bicarbonate ions to enable the body cope with acid base balance.

Question 33

Why is Hb important regarding CO2?

Answer 33

For the CO2 flux in and out of the tissues and lungs

Question 34

What is the significance of the Haldane effect?

Answer 34

HCO3 + H+ions is made and then moved into the plasma.
DeoxyHb is a strong proton acceptor
Therefore will mop up H ions
Therefore CO2 will be bound to Hb but also form more HCO3

Question 35

What are the transport rates between the arterial and venous blood for O2 and CO2.

Answer 35

VCO2 = 200ml/min

VO2 = 250 ml/min

Question 36

What is the Haldane effect?

Answer 36

Since deoxyhaemoglobin has a higher affinity for CO2, when PO2 falls which leads to a rising CO2.
Therefore it makes it easier to transport CO2.

Question 37

What happens to the affinity Hb has for O2 in acidosis?

Answer 37

Affinity decreases.