Lecture 6 - Gas transport

Question 1

What are the two ways O2 is transported in the blood?

Answer 1

1. Dissolved in bood​

• For each mmHg only 0.03 ml of O2 is dissolved per litre of blood.
• Therefore 1 litre of blood at 100mmHg will have three 3ml of O2.

Dissolved O2 is not very effective for transport, need to use haemoglobin.

2. Combined with haemoglobin

• O2 binds reversibly to Hb to give oxyhaemoglobin
  
  • binding depends on PO2 (relates to dissociation curve)

Question 2

What is O2 saturation?

And what are the O2 saturations in arterial and venous blood?

Answer 2

O2 saturation is the percentage of available binding sites that have O2 attached.

The O2 saturation of arterial blood (SaO2) with a PO2 of 100mmHg is ~98mmHg.

O2 saturation of venous blood (SvO2) with a PO2 of 40mmHg is ~70%.

Question 3

What does 002550 4070 7090 100 100 mean?

Answer 3

25mmHg gives you 50% saturation

40mmHg gives you 70% saturation

70mmHg gives you 90% saturation

100mmHg gives 100% saturation

Question 4

The upper part of the sigmoidal curve is flat, what impact does this have?

And what siginificance does the steepness of the lower part of the curve have?

Answer 4

This means that changes in pO2 have a small impact on Hb saturation.

The steeper lower curve means that changes in pO2 will result in rapid O2 loading or offloading.

Question 5

What is O2 capacity?

And how do you calculate it

Answer 5

The maximal amonut of O2 that can be combined with Hb is the O2 capacity (when Hb is 100% saturated).

Normal blood is about 150g/L, and one gram of Hb can combine with 1.34 ml O2.

O2 capacity = 1.34 x 150 = 200 ml/litre of blood

Question 6

What is the O2 content?

Answer 6

It’s O2 capacity x saturation

so it’s maximal amount of O2 that can combine with Hb multiplied the proportion of available binding sites that have bound O2.

Question 7

Describe left and right shifts in the O2-Hb dissociation curve (Bohr effect)

Answer 7

Left for loading = in lower pH conditions (lower H+ and CO2), lower temp, you get a left shift, which helps with loading O2 more easily onto Hb.

So a left shift means more O2 loading for a given pO2 in the lungs.

A right shift facilitates release of O2. Right shit occurs in elevated H+ conc, PCO2, temp, 2,3-DPG. A shift is occurs more for exercising tissues, since it is acidic, hypercapnic, and hot, and it benefits from increased unloading of O2.

A right shift means more O2 unloading for a given pO2 in tissues

Question 8

What is 2,3 DPG?

Answer 8

It’s a by-product of glycolysis

2,3-DPG increases with intense exercise training, altitude and due to severe ung diseases or anemia

It helps deliver O2 to tissues (due to right shift of ODC which allows more O2 to be released from Hb for a particular PO2)

So 2,3-DPG assists in causing right shift, so helps with unloading O2 in exercising tissues

Question 9

What is cyanosis?

And what is central, and peripheral cyanosis?

When does it become detectable?

Answer 9

Cyanosis is caused by low O2 saturation/content.

It has a blue-purple colour, most obvious in the skin, nail beds and mucosal membranes, caused by lower SaO2 and is indicative of blood with a low CaO2.

Detectable when there is at least 50 g/l of deoxy-haemoglobin (also depends on skin pigmentation, illumination and adequate capillary perfusion)

Question 10

What are the two ways O2 is transported in the blood

Answer 10

It is either dissolved, or combined to haemoglobin

Question 11

How do you calculate the O2 content of arterial blood?

Answer 11

Question 12

What difference can be seen in the O2 saturation curve for anaemic patients?

Answer 12

Their saturation curve stays the same, but the O2 content gets reduced.

For most anaemic people it is asymptomatic, but when they exercise, causing an increase in A-a difference, they begin to experience symptoms.

Question 13

How does CO affect O2 transport and content?

How does it affect the saturation curve?

Answer 13

CO interferes with O2 transport by combining with Hb to form carboxyhaemoglobin COHb - this blocks O2 binding sites, so it is essentially like anaemia - there are less binding sites for O2.

CO has ~250 times the affinity of O2 for Hb.

Small amounts of CO can bind to a large proportion of Hb in the blood, making it unavailable for O2 carriage, thus reducing O2 content.

CO shifts the curve to the left, it makes it more difficult to unload O2 to tissues (requires a lower pO2 for O2 be released).

Question 14

What are the three forms that CO2 is transported as?

Answer 14

1. Dissolved in plasma (10%)
2. As bicarbonate (70%)
3. Combined with proteins (20%)

Question 15

What is the haldane affect?

Answer 15

Deoxygenated blood is more likely to bind CO2

This also means that when the blood returns to the lungs it is now less likely to bind CO2 since it’s more oxygenated, therefore it facilitates CO2 unloading

Question 16

How is CO2 converted to bicarbonate so it can be transported?

And how are carbamino compounds formed (20% of CO2 transport)

Answer 16

• Bicarbonate is formed in red blood cells by carbonic anhydrase
• Carbamino compounds are formed by the combination of CO2 with terminal amine groups on blood proteins, mostly Hb

Question 17

Summarise the haldane effect in one sentence

Answer 17

Deoxygenation of blood helps CO2 carriage

Question 18

Describe the affects of the haldane and bohr effects in:

The lung

And the tissues

Answer 18

Haldane and bohr effect in lungs

in the lungs haldane affect facilitates CO2 offloading since the Hb oxygenations increases.

Bohr effect facilitates O2 loading due to leftward shift in O2 sat curve due to reduced concentrations of CO2, BPG and lower temp.

Haldane and bohr effect in tissues

Haldane affect causes increased CO2 loading since Hb is more deoxygenated, which means its more likely to bind CO2.

Bohr effect facilitates O2 release due to the rightward shift caused by increased CO2 & BPG conc. and higher temp.