Lecture 35 - Respiratory System: Gas Transport and Exchange Flashcards
What is partial pressure (P)?
Pressure exerted by a single gas within a mixture of gas
T/F? The partial pressures of oxygen, carbon dioxide, and water are similar at the alveoli and outside air
False - The partial pressures of oxygen, carbon dioxide, and water are different at the alveoli than in the outside air
What can contribute to the difference in partial pressures in the alveoli vs. the outside air?
Alveolar air has mixed newly inhaled air with the used air that could not be fully exhaled because of anatomical dead space
Explain Henry’s Law in terms of dissolved gas and partial pressure
The amount of dissolved gas in a solution is proportional to partial pressure of that gas in the air
What is being diffused in external respiration and across what?
It involves diffusion of gases between blood and air across the alveolar and capillary walls
What are the PO2 and PCO2 levels in external respiration?
Blood arriving at pulmonary capillaries is deoxygenated (low PO2) and relatively high in PCO2
Describe the O2 and CO2 exchange between the pulmonary capillary and alveolus in external respiration
The thin wall created by alveolar type I cells and pulmonary endothelial cells allow for O2 to diffuse into blood, and CO2 to diffuse into the alveolar cavity
What is being diffused in internal respiration and across what?
It involved diffusion of gases between blood and ISF across capillary walls
What are the PO2 and PCO2 levels in internal respiration?
Blood arriving at systemic capillaries is oxygenated (high PO2) and relatively low in PCO2
Describe the O2 and CO2 exchange between the systemic capillary and peripheral tissue in internal respiration
Oxygen diffuses down its concentration gradient into tissue, while the pressure gradient favours the uptake of CO2 in blood
What are the 3 factors that rate of diffusion is affected by?
- Pressure gradient
- Surface area
- Thickness of the barrier
Explain Fick’s Law in terms of how it enhances rate of diffusion
Diffusion of a gas at a given temperature is enhanced by a large surface area, and a steep partial pressure gradient. It’s reduced by a thick barrier
At a resting state, is blood gas composition at equilibrium before it exits the capillary bed? Why?
Yes - by the time blood reaches the venules, blood PO2 and PCO2 have both been able to equilibrate with the surrounding tissue (alveolar or peripheral tissue). If pressure gradients change (ex. due to exercise), this may not be the case anymore)
How can respiratory reflexes increase the rate of gas exchange at the alveoli regarding pressure gradients?
By refreshing the pressure gradients - increasing respiratory rate will increase the exchange of air between the outside and the alveoli, refreshing the partial pressure gradients
Therefore, rate of diffusion is the greatest when the difference in partial pressure is greatest
How can respiratory reflexes increase the rate of gas exchange at the alveoli regarding surface area?
Increasing functional alveolar surface area - increasing tidal volume will further inflate the alveoli, increasing surface area for diffusion (and potentially slightly decreasing barrier thickness)
