Gaseous Diffusion and Transport 2 Flashcards
What is a normal resting O2 consumption?
250ml/min.
What is the O2 saturation and O2 content of the blood entering the pulmonary capillaries via the pulmonary arteries?
It is 75% saturated.
It contains around 150ml/litre of O2.
What is the O2 saturation and O2 content of the blood exiting the pulmonary capillaries via the pulmonary veins?
It is 95-100% saturated.
It contains around 200ml/litre of O2.
What is stored blood low in which reduces its oxygen carrying capacity?
It is lower than normal blood in 2, 3 DPG, which will mean the blood has an increased oxygen affinity (left oxygen-dissociation curve shift) which means it will be impaired with respect to oxygen carrying/offloading.
Roughly what amount of oxygen do the tissues extract at rest?
5ml/dL
NB: units in dL, NOT L!!
What effect on the oxygen-dissociation curve will anaemia have?
In anaemia there is a reduced content of functional Hb and therefore a reduction in O2 carrying capacity. This will be seen as the same sigmoid shape on the oxygen-dissociation graph but shifted downwards, so the maximal O2 content is reduced.
What will an anaemic patient’s arterial and venous PO2 roughly be?
What does this indicate for further gas exchange above the baseline requirements?
Their PaO2 (arterial) will start at 12.5kPa the same as a healthy patients, but by the time the blood reaches the pulmonary circulation and the standard 5ml/dL of oxygen has been removed by the tissues their PO2 will have dropped lower than a healthy persons.
A healthy persons drops to around 5.3kPa.
An anaemia patients drops to around 3.6kPa.
This is because in a patient with anaemia 5ml/dL makes up a larger percentage of their oxygen content at 12.5kPa (10ml/dL as opposed to 20ml/dL), therefore the reduction in PO2 when this 5ml/dL is taken is greater.
The implication of this is that they have a decreased PO2 remanining after baseline deductions (5ml/dL) to meet any extra demands such as exercise.
Up to how many times greater is Hb’s affinity for CO over O2?
X240!
What is the name of the compound formed when Hb binds with CO?
What colour is the compound?
Carboxyhaemoglobin.
Dark cherry-red.
What does the formation of carboxyhaemoglobin during CO poisoning do to the shape of the oxygen-dissociation curve?
1) It moves it down, as the total amount of O2 the blood can carry is reduced due to CO competing for the same binding sites as O2.
2) It also moves it to the left (dangerously), meaning the O2 which managed to bind to Hb has an increased affinity for it and is not easily released, resulting in decrease unloading of O2 to the tissues.
What is the composition of:
1) adult Hb
2) regal Hb
1) adult Hb
= X2 alpha chains
= X2 beta chains
2) foetal Hb
= X2 alpha chains
= X2 gamma chains
What are the X3 forms in which CO2 is carried in the blood, including percentages?
1) as bicarbonate (HCO3-) in both the plasma and RBC’s = 60%
2) as carbamino compounds such as HbCO2 = 30%
3) dissolved as CO2 in the plasma = 10%
The reaction of CO2 to bicarb for transport is faster in either the plasma or the RBC’s.
In which is it fastest and why?
What does CO2 combine with to form bicarbonate?
It is faster in the RBC’s as they contain an enzyme responsible for speeding up this process, carbonic anhydrase.
CO2 + H2O —> H2CO3 —> HCO3- + H+
What do the hydrogen ions created in the bicarbonate reaction bind to?
Hb.
What happens to the majority of the bicarbonate produced inside the RBC to aid CO2 transport?
What is the name of this process?
It diffuses out of the RBC’s and into the plasma via an anti porter paired with chloride ions (which enter the RBC’s).
It is called the chloride shift.
