Gas transport (O2) Flashcards
How many ATP molecules does each glucose molecule produce in the presence of oxygen (aerobic)?
36-38
How many ATP molecules does each glucose molecule produce in the absence of oxygen (anaerobic)?
2
What is the oxygen cascade?
The oxygen cascade describes the transfer of oxygen from air to mitochondria. In each step of the cascade the PaO2 falls. It demonstrates that oxygen delivery to tissues relies on the passive transfer of gas down partial pressure gradients.
What is a typical resting oxygen consumption?
250ml/min
Describe the structure of heam
Haem is a porphyrin compound coordinated to a single iron ion. Iron is in its ferrous form (Fe2+).
Describe the structure of haemoglobin
A tetramer - 2 alpha and 2 beta globin polypeptide chains
Haemoglobin A - main adult form
Each coiled polypeptide chain has one haem group attached
Overall molecule has a complex quaternary structure
Structure influenced by various factors and its modification alters the oxygen affinity of the molecule – cooperative binding.
Compare the differences between relaxed and tense haemoglobin
Relaxed haemoglobin has a much higher oxygen affinity – an open and receptive conformation allows oxygen access to haem groups
Tense haemoglobin has a conformation that inhibits oxygen binding and thus binds oxygen ~500 times less strongly than in the relaxed state
These conformations are influenced by the environment (surrounds pO2), binding of oxygen and binding of other molecules
What is meant by cooperatively between the oxygen binding sites in haemoglobin?
As haemoglobin binds oxygen to one haem group, the conformation of the whole tetramer changes and becomes more open
This change in conformation makes binding the next oxygen molecule much easier – there is cooperativity between the oxygen binding sites
Binding becomes progressively easier as more oxygen molecules are bound
Describe why the dissociation curve of oxygen has its shape
Initially the curve of oxygen binding as pO2 increases is shallow
Binding changes conformation, increases oxygen affinity and facilitates further binding
The curve steepens rapidly as pO2 rises until saturation where it levels out
These changes in affinity with binding create a sigmoid dissociation curve
At what pO2 does the dissociation curve reach a plateau?
~8kPa and is ~90% saturated
What is the oxygen saturation (%) of haemoglobin below 1kPa?
Virtually unsaturated
At what pO2 is haemoglobin half saturated (50%)?
~3.5 kPa
What is alveolar pO2 and what does this mean?
Alveolar pO2 is 13.3.kPa and therefore haemoglobin is almost fully saturated at ~95%
*What is the typical oxygen concentration for fully saturated haemoglobin?
~200ml/L
So or calculations, you would multiply change in oxygen saturation x 200
Amount of oxygen delivered per litre of blood = (change in oxygen saturation as a decimal) x 200
What is the typical pO2 of tissues at rest?
~6kPa and haemoglobin is not ~65% saturated
What factors cause the dissociation curve to shift to the right?
Acidity, increased temperature, increased CO2 and increased 2,3-DPG cause a shift to the right and thus decrease oxygen affinity
Major shift occurs at tissues favouring oxygen being offloaded where it is needed
2,3 diphosphoglycerate (2,3-DPG) levels increase in red blood cells in response to hypoxia – stabilises tense state
What is the Bohr effect?
This refers to the fact that in acid conditions the oxygen dissociation curve shifts along the pO2 axis
This is due to hydrogen ion and carbon dioxide binding which both stabilise haemoglobin in the tense state
Result is that at any given pO2 haemoglobin binds less oxygen
Oxygen is thus released more easily in the tissues where the pH is more acidic and CO2 in higher concentration
What is the Haldane effect?
Conversely to the Bohr effect….
Increasing oxygen binding to haemoglobin (in lungs) reduces the affinity for carbon dioxide and hydrogen ions by modifying the haemoglobin conformation
This is effective at the level of the pulmonary capillaries and results in more CO2 being offloaded at the lungs
What are some adaptations to chronic hypoxia?
1) Increased erythropoietin (EPO) production
2) Increased tissue capillary density
3) Increased 2,3-DPG levels
4) Increased ventilation
