Session 3: Oxygen in the Blood Flashcards
Why is haemoglobin needed for oxygen to be transported sufficiently and efficiently?
Because oxygen is not sufficiently soluble in body fluids. Binding to haemoglobin also allows the partial pressure gradient to remain low and towards the capillary system. This allows more oxygen to be perfused as well.
What is the arterial partial pressure of oxygen leaving the lungs?
13.3 kPa
Difference between haemoglobin and myoglobin.
Hb found in blood and a tetramer binding 4 O2
Mb found in muscle cells and a monomer binding 1 O2
Explain the Oxygen-Haemoglobin dissociation curve.
It is a sigmoid curve with arterial partial pressure of O2 found on its x-axis and the saturation of oxyhaemoglobin in percentage on its y-axis.
As the paO2 increases more and more haemoglobin will become saturated. At around 13.3 kPa all it will plateau as 100% saturation has been reached.
If we have a paO2 exceeding 13.3 kPa. What will happen to the O2 in the blood?
It will dissolve into the blood. In a healthy individual with healthy lungs an increased paO2 is not beneficial as all of the haemoglobin has been saturated.
Solubility of oxygen is low as well so increasing pO2 will not have a significant increase of oxygen content in the blood.
What is a shift of the dissociation curve of haemoglobin and oxygen?
Means oxygen will be either more or less released by haemoglobin.
What does a shift to the right mean of the dissociation curve?
What does a shift to the left mean?
It means that O2 will be more readily released from the haemoglobin.
It means that haemoglobin will have higher affinity to oxygen and so oxygen will not be as readily released.
Give factors that will affect the affinity of haemoglobin to oxygen.
Explain whether the factors will shift the curve to the right or left.
pH - decrease pH shifts the curve to the right
Temperature - higher temperature shifts the curve to the right
2-3 DPG - Increased amounts shifts the curve to the right
CO2 - increased amounts shifts the curve to the right
What is Bohr’s shift?
A shift of the haemoglobin oxygen dissociation curve based on solely pH.
How can adequacy of oxygenation be measured?
Oxygen saturation
Arterial blood gas analysis
Explain oxygen saturation briefly by pulse oximetry.
O2 saturation is estimated using a pulse oximeter.
A quick non-invasive technique and is useful for monitoring the patient’s oxygenation status.
It works on the principle that Oxy-Hb and desaturated Hb in capillary lood absorb light of different wavelengths. However this does not say how much Hb is present.
It also ignores the levels of oxygen in tissues and non-pulsatile venous blood and only detects the arterial pulsatile blood.
Explain arterial blood gas analysis briefly.
Requires an arterial blood sample.
Obtained by arterial puncture usually from the radial artery. This is not quick, and it is invasive.
Give normal Hb concentration.
2.2 mmol/l
If normal Hb concentration is 2.2 mmol/l, what is normal oxygen content of arterial blood?
Since each Hb molecule binds four O2 molecules the oxygen content of the blood will be 8.8 mmol/l
Explain carbon monoxide poisoning.
Reacts with Hb to form CO Hb. CO has a high affinity to it and binds irreversibly.
This renders that Hb useless as it increases affinity of unaffected subunits for O2. This means that the Hb will not give up O2 at tissues. This means that the amount of oxygen bound can be more or less the same in a healthy and not healthy person but the one with CO poisoning might die since the O2 is not being given to the tissue.
