Principles of Gas Exchange Flashcards
What is the partial pressure of a gas in a mixture of gases?
The pressure that it would exert if it was the only gas in the container
What is the universal gas equation?
PV = nRT
What is the pressure gradient between alveolus and blood?
The difference in partial pressure of the respective gases in the alveolus and blood
What is partial pressure?
The partial pressure of a gas in a mixture of gases is the pressure that it would exert if it was the only gas in the container
What is Dalton’s Law?
Partial pressure = total pressure x fractional concentration of gas
Why is the partial pressure of O2 lower than in room air?
- Inspired air is humidified in the upper airway
- In the alveoli, O2 is taken up while CO2 is added so CO2 dilutes air and partial pressure of O2 drops
- Body consumes more O2 molecules than it produces CO2 molecules
What factors determine the values of alveolar pO2 and pCO2?
- The pressure of outside air
- The partial pressures of inspired O2 and CO2
- The rates of total body O2 consumption and CO2 production
- The rates of alveolar ventilation and perfusion
What is the partial pressure of water vapour?
6.3 kPa
Where does gas exchange occur in the body?
In the lungs - O2 is picked up and CO2 is released at respiratory membrane
At the tissues - O2 is released and CO2 is picked up
What is external respiration?
Exchange of gases with the external environment and occurs in the alveoli of lungs
What is is internal respiration?
Exchange of gases with the internal environment and occurs in the tissues
How does the anatomy of the lung maximise diffusion?
- Respiratory membrane is highly permeable to gases
- Respiratory and blood capillary membranes are very thin
- Large SA throughout lung
What does external respiration occurs as a result of?
Partial pressure differences in O2 and CO2 between the alveoli and the blood in the pulmonary capillaries
Describe gas exchange during external respiration
- Pulmonary artery carries deoxygenated blood from the heart to the lungs
- This artery branches and becomes the capillary network composed of pulmonary capillaries
- These pulmonary capillaries create the respiratory membrane with the alveoli
- As blood is pumped through this network, gas exchange occurs
Small amount of O2 dissolves directly into plasma from alveoli, most picked up by RBCs and binds to Hb
What happens to O2 and CO2 during gas exchange of external respiration?
Small amount of O2 dissolves directly into plasma from alveoli, most picked up by RBCs and binds to Hb
CO2 released in opposite direction, from blood to alveoli.
What is the partial pressure of O2 in the alveolar air vs in the blood of the pulmonary capillaries?
What does this difference create?
Partial pressure of O2 in alveoli –> 13.8 kPa
Partial pressure of O2 in blood of capillary –> 5.3 kPa
A very strong pressure gradient, causing O2 to rapidly cross the respiratory membrane from the alveoli to the blood
What is the partial pressure of CO2 in the alveolar air vs blood in of the pulmonary capillaries?
Why does it not matter that the difference in partial pressures is smaller?
Alveoli –> 5.3 kPa
Capillary –> 6.0 kPa
The solubility of CO2 is much greater than that of O2. As a result, the relative concentrations of O2 and CO2 that diffuse across the respiratory membrane are similar
What does internal respiration occur as a result of?
Partial pressure gradient between blood and tissues
O2 diffuses out of blood and into tissues
CO2 diffuses out of tissues and into blood
Why is partial pressure of O2 in tissues low?
O2 is continuously used for cellular respiration
What is partial pressure of O2 in blood vs tissue?
What is result of this difference?
Blood –> 13.3 kPa
Tissues –> 5.3 kPa
Pressure gradient causes O2 to dissociate from Hb, diffuse out of blood, cross interstitial space and enter tissues
Why is partial pressure of CO2 higher in tissues than blood? What is result of this?
Cellular respiration continuously produces CO2 so partial pressure is higher in tissues than blood
CO2 diffuses out of tissues into blood and carried back to lungs (via Hb, dissolved in plasma or converted form)
What does a greater difference in partial pressure result in?
A more rapid movement of gas
What does alveolar air contain in comparison to atmospheric air (water vapour, CO2, O2)
- Greater amount of water vapour
- Greater amount of CO2
- Less O2
How many O2 molecules are consumed for every CO2 molecule produced?
About 1.25x
How does the partial pressure of a gas relate to its solubility?
Higher solubility = lower partial pressure (inversely proportional)
Lower solubility = higher partial pressure (hydrophobic molecules attempt to push out as much as possible)
If gas is more soluble, then more molecules are needed to achieve the same partial pressure
Is CO2 more or less soluble than O2? How does this affect its partial pressure?
Approx 24x more soluble in water than O2 –> achieves less partial pressure for given number of molecules in solution than O2
