Respiration 3 - Blood Flow and Gas Transfer Must Match
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What is the total expired volume? What is it denoted as?
Total expired volume is the total expired breath collected per minute. It is denoted as VE
What is the ideal ventilation:perfusion ratio?
At rest how long does a RBC spend in transit over an alveolus?
Venous blood arrives in the lung with an oxygen tension of ...?
How long does it take blood and alveolar air PO2 to equilibrate during transit time?
They equilibrate within 1/3 of transit time
What effect does disease of the alveoli have on oxygen uptake in the lungs?
Disease of the alveoli thickens the diffusional barrier and limits O2 uptake by slowing the equilibration time. In a diseased lung blood can leave the capillary circuit without having become equilibrated with alveolar air.
At low PO2 (e.g. high altitude) O2 diffusion will be faster/slower?
Slower, and ultimately gas tension will be lower
List different reasons why hypoxic hypoxia can occur
High altitude, the air conducting system in your lungs is blocked, breathing a mixture with high nitrogen/low oxygen
How does anaemic hypoxia differ from hypoxic hypoxia?
In anaemic hypoxia there is nothing wrong with the ability of the lung to achieve alveolar oxygen tension or the diffusing capacity of oxygen so blood will still have equilibrated with alveolar air but the oxygen content will not be as high. (Anaemic hypoxia = correct oxygen tension, lower oxygen content. Hypoxic hypoxia = low arterial oxygen tension).
Would increasing the ventilation rate/breathing pure oxygen help increase the oxygen tension in the blood?
The Hb curve is saturated at around 100mmHg, so if you go above this you may get a little more oxygen dissolving into the plasma but not much as the Hb is already saturated
Describe the ventilation perfusion mismatches that may be seen in the following areas of a large animal lung a) close to the heart, in the ventral lung field b) in the centre of the lung c) in the caudo-dorsal lung field
- a) Perfusion will be fine as this area of the lung is located close to the heart. However, secretions can accumulate in the ventral aspect of the lung and limit ventilation.
- b) Ideal gas transfer occurs here
- c) There is very good ventilation but poor perfusion (as the right side of the heart has difficulty pumping the blood to the dorsal lung field).
The outcome of a ventilation perfusion mismatch is always ...?
During mixing of blood in the lung, why can higher levels of oxygen in one area not compensate for lower levels of oxygen in another?
As the Hb curve does not allow for overloading of oxygen
What receptors will be activated during hypoxic hypoxia (low PO2)?
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