Week Three - Gas Exchange Flashcards
What are the factors that affect the diffusion rate of a gas or a fluid?
The pressure difference The solubility of the gas in solution The cross sectional area of the fluid The distance the molecules must diffuse The molecule weight The temperature of the fluid
What is the distance between the blood and the air within the alveoli?
0.6nanometres
Why is the concentration gradient between the the capillaries and the alveolar smaller but yet they still travel across it?
Carbon dioxide has a high solubility.
What are the five layers that the gas has to dissolve through to get to the alveolar?
Red blood cell membrane Plasma Endothelial cell of capillary Tissue fluid Epithelial cell of alveolus
What are the values of the oxygen and carbon dioxide content in the alveolar gas?
PO2 is 13.3kPa
Pco2 is 5.3kPa
Why is it important for the blood/alveolar gases to equilibriate in 1/3 of the time that the blood is in contact with the alveolar?
Because during exercise the time will be shorter.
Why does co2 diffuse faster than o2?
Because whilst oxygen is smaller it is less soluble and therefore co2 moves twenty times faster.
On average what is the functional residual capacity of the the lunches and what is the alveolar ventilation volume per breath?
Frc is 2300ml and the new respiratory volume per breath is 350ml. Therefore the volume of new air in any breath is 1/7th
Why is it important that only 50% of air is exchanged when breathing normally in 17 seconds?
Guards Against sudden changes therefore respiratory system is more stable
What is the alveolar ventilation rate?
The amount of air that actually reaches the alveoli. Need to account for the wasted air in the dead spaces in order to calculate.
When would the ventilation perfusion value be less than one and when would it be more?
Clue V/Q
Less than one is because there is a problem with the ventilation so V is low eg mucous plug - no air inspired
More than one is because there is a problem with perfusion so Q is low eg PE - no perfusion
What is the serial dead space?
The anatomical dead space - the volume of the airways
How is the serial dead space measured?
Nitrogen wash out
What is the average value of the serial dead space?
0.15l
What is the distributive dead space?
Dead or damaged alveoli or alveoli with poor perfusion. Typically 0.02l
