Gas Transport - Oxygen

Question 1

What is the purpose of oxygen transport in the blood?

Answer 1

Oxygen is required for life and the production of ATP from glucose. Oxygen delivery must match utilisation!

Question 2

What is resting oxygen consumption?

Answer 2

~250ml/min

Question 3

How is oxygen transported in the blood stream?

Answer 3

Rapid reversible chemical reaction with haem compound in RBC.

Question 4

What is haem?

Answer 4

Porphyrin compound coordinated to single iron atom (Fe2+) - red colour when saturated with O2, purple when not

Question 5

What is haemoglobin?

Answer 5

Tetramer - 2 alpha + 2 beta global chains
Main adult form = haemoglobin A

Each coiled polypeptide chain has 1 haem and 1 globin component

Question 6

What configurations can Hb exist in?

Answer 6

2 main configurations - tense + relaxed

Question 7

Is the affinity for oxygen different in relaxed and tense Hb configuration?

Answer 7

Relaxed Hb = higher O2 affinity (open + receptive quaternary structure allows O2 to access haem groups)

Tense Hb = lower O2 affinity (quaternary structure doesn’t allow access to haem, binds with less avidity)

Question 8

How is the configuration of Hb affected?

Answer 8

Influenced by environment (pH, temp)
Binding of oxygen
Binding of other molecules

When pO2 = low, no O2 bound + Hb is tense, hard to bind 1st O2 molecule (requires threshold minimum pO2)
As Hb binds O2 to 1 chain, quaternary structure modifies and becomes relaxed
This makes next oxygen molecule binding easier + reflects cooperativity between oxygen binding sites.

Question 9

What is an Oxygen Hb dissociation curve?

Answer 9

Amount of O2 bound to Hb against partial pressure of O2

Question 10

What can an Oxygen Hb dissociation curve be used for?

Answer 10

Delineate how much oxygen will be bound/given up when blood is moved between areas of different partial pressure of O2

Question 11

What does the curve of an Oxygen Hb dissociation curve show?

Answer 11

Chemical binding becomes saturated above given pO2

Amount of O2 bound then depends on how much Hb available

Saturation is independent of Hb conc

Question 12

Describe the shape of the curve on an oxygen-Hb dissociation graph

Answer 12

Initially relationship between pO2 and binding = shallow
Binding changes Hb configuration which increases O2 avidity and facilitates further binding
Curve steepens rapidly as pO2 rises until saturation where it levels out

Sigmoid shape!

Question 13

What is alveolar pO2 approximately?

Answer 13

13.3kPa (almost fully saturated at ~95%)

Question 14

What is tissue pO2 approximately?

Answer 14

~6kPa at rest (Hb saturation ~65% as has given up 30% of oxygen at tissues)

Question 15

What is venous blood pO2 approx?

Answer 15

Resting state = 50% saturation (at tissue level Hb could possible release more O2 if metabolism increase)

OXYGEN RESERVE

Question 16

If tissue oxygen tension (tissue pO2) is lower, more O2 will be…

Answer 16

Given up by Hb as it diffuses down increased gradient more quickly + as more O2 loss Hb has lower affinity for O2

Question 17

What conditions result in more tense Hb?

What is this effect called?

Answer 17

Low pH
High temp
Increase CO2
Increase 2,3-DPG (levels of this increase in RBCs in response to hypoxia)

Cause shift of dissociation curve to right = H+ ion and CO2 binding stabilise Hb = decrease O2 affinity = favours oxygen offload into tissues

Bohr Effect

Question 18

What is the Haldane Effect?

Answer 18

Increasing oxygen binding to Hb in lungs reduces affinity for CO2 and H+ ions by modifying quaternary structure = results in ore CO2 offloaded into lungs

Question 19

What are the long-term physiological adaptations to chronic hypoxia?

Answer 19

Chronic hypoxia triggers various adaptive responses to attempt to increase O2 delivery to tissues
The physiological adaptations depend on cause but are:
- increase EPO producing causing increased RBC production
- increase tissue capillary density
- increase 2,3-DPG levels
- increased ventilation