Gas Transport Flashcards
What are the 2 main gases involved in gas transport?
Oxygen and carbon dioxide
What are the 2 ways oxygen can be carried around the body?
- dissolved in plasma
- carriage by haemoglobin
What are the main characteristics of O2 dissolved in plasma?
- proprtional to partial pressure
- O2 is poorly soluble
How much oxygen does blood with a PO2 of 100mmHg contain?
0.3ml O2 /100ml blood
What is the most inefficient way to deliver oxygen around the body?
Oxygen dissolved in the plasma
What are the tissue requirements of oxygen for the body at rest?
250ml O2/min
What is meant by the terms haem and globin?
Haem = iron containing compound
Globin = protein of 4 polypeptide chains
What does oxygen and haemoglobin form?
easily reversible combination of oxyhaemoglobin
HbO2
How many binding sites does each haemoglobin have?
4
What does positive co-operative binding mean?
once the first O2 is bound, the next three bind easier
What does affinity of Hb for O2 change with?
increases with the extent of Hb saturation
What is the shape of the oxygen-haemoglobin dissociation curve?
sigmoidal
Describe the 5 main aspects of gas transport that relate to this curve
- In the lungs PO2 is high, so Hb is fully saturated
- At tissue level PO2 has fallen by more than half but the Hb is still saturated at 75% (PO2 doesn’t alter saturation)
- Flat upper plateau means that even when PO2 falls saturation is not greatly altered
- Steep lower part means that tissues can extract lots of O2 for a small drop in PO2
- 25% is normally unloaded at tissues, leaving a large reserve without needing to increase respiratory rate or cardiac output
How do an increase in:
- temperature
- H+
- CO2
- 2,3-bisphosphoglycerate
affect the oxygen-haemoglobin saturation curve?
Shift the curve to the right
How do an increase in:
- temperature
- H+
- CO2
- 2,3-bisphosphoglycerate
affect Hb’s affinity for O2?
All modify the 3D structure of Hb, decreasing affinity for oxygen hence the shift to the right
e.g. warmed muscles are better at releasing O2
How does CO2 affect Hb’s affinity for oxygen?
Increasing CO2 leads to an increase in H+ which weakens the Hb-O2 intertaction causing the Bohr-Effect to occur