S3 L2 Oxygen Transport Flashcards
Oxygen transport:
- How to work out the concentration of oxygen dissolved in the blood?
- What is cardiac output per minute
- Maximum cardiac output?
Max. CO: 20-25L/minute
Oxygen Binding
- Required properties of carrier
- Structure of haemoglobin
- Where does oxygen bind?
- Carrier reaction needs to be reversible
- Carrier must associate with oxygen at the lungs
- Oxygen must dissociate from carrier at tissues to
supply them - Many substances will bind oxygen but only some
are useful - above requirements - Our carriers - Respiratory pigments containing
haem group - in blood- haemoglobin - Oxygen combines reversibly with iron in haem
- Stays as molecular oxygen
What is an haemoglobin-oxygen dissociation curve?
- axis
- shape of graph
- what does it tell us?
• Graph showing how changes in partial pressure of oxygen change haemoglobin saturation - how much O2
• Saturation is expressed as the percentage of pigment that has bound oxygen against
100% saturation - independent of pigment concentration
• For example, if there were only one haemoglobin molecule in your body but it was carrying 4 oxygen molecules it would be 100% saturated
• Haemoglobin saturation itself therefore does not tell us how much haemglobin is in blood
What does it tell us:
– What percentage of Haemoglobin is carrying O2
– Relationship between the partial pressure of oxygen
and haemoglobin saturation
– How easy or difficult it is to saturate/desaturate
haemoglobin depending on part of curve
- Shows how much O2 will be bound or given up when moving from one partial pressure to another
- Work out difference in percentage saturations between two pO2 values
- Work out the effects of changed conditions on how easily haemaglobin binds or releases oxygen
- Infer the partial pressure and hence the dissolved levels of oxygen by looking at the saturation – NB: infer, not directly measure.
(Concentration dissolved oxygen = partial pressure x solubility
Basis for haemoglobin cooperativity
- What is this?
Look at MCBG notes
Haemoglobin states
- 2 types and explain
- Safe zone and danger zone on the Haemoglobin-saturation curve
- Low affinity for oxygen in T state (tense) – Difficult for oxygen to bind TENSE
- High affinity for oxygen in R state (relaxed) – Easier
for oxygen to bind RELAXED - When pPO2 is low Hb is tense
• So it is hard for the first O2 molecule to bind
• As each O2 binds the molecule becomes more relaxed and
binding of the next O2 molecule is easier + Cooperativity
Oxygen content on haemoglobin - how to calculate?
How does anaemia affect the oxygen ‘levels’ in the blood
Anaemia:
Have less hb but the hb is all saturated, so hb saturation’s can still be normal in anaemia, the oxygen content of the blood will be lower
Summary: Oxygen in Blood and Tissues
- Recap so far, read to check understanding
pic
Haemoglobin in the tissues
pic
Haemoglobin in venous blood
What is the range for partial pressure of oxygen in venous blood?
5.3-6kPa
How low can tissue pO2 get?
- must be high enough too…
- can’t fall below ____ in capillaries
- What adaptions can reduce the pO2 in tissue?
- Examples of when this happens?
pic
Oxyhaemoglobin % saturation
- What causes the left shift of this graph
- What causes the right shift of this graph
Also:
Temperature -
Higher temperature the curve shifts to the right – more oxygen released
Metabolically active tissues - have higher temperature
2,3 BPG -
2,3-DPG, Also called 2,3 -BPG
2,3- diphosphoglycerate
(or biphosphoglycerate)
2,3-DPG is an intermediate of RBC glycolysis normally rapidly consumed but in hypoxia RBC production of 2,3 DPG increases - facilitates O2 unloading in tissues. 2,3-DPG levels drop
in stored blood due
to refrigeration
Pathological shifting haemoglobin
- Carbon monoxide
- How does this affect the haemoglobin-oxygen curve
- Risk factors for CO
- Signs and symptoms of CO poisoning
• Fatal if HbCO is > 50%
• Children at increased risk
partly because they
breathe faster
• Does not decrease PaO2
Six:
• Headache
• Nausea
• Vomiting
• Slurred speech
• Confusion
• Initially may not have many respiratory symptoms
Hypoxemia or hypoxia
- What are they both?
- Examples of when hypoxia occurs? (conditions)
pic
Cyanosis
- What is this?
- 2 types of cyanosis
- Why can it be difficult to detect?
pic
Peripheral cyanosis
- What is this?
- Signs?
Central cyanosis:
- What is this?
- Signs
pic
Pulse oximetry vs Arterial Blood Gas Analysis:
- What does it measure
- Units
- How is it measured
- When would this method be appropriate to assess oxygenation
- Limitations of the method
Pulse oximetry to add:
- Only detects pulsatile arterial blood levels
- Can’t detect tissue oxygen levels or non-pulsatile venous blood
- Can’t give information about Hb levels
