When our teacher was talking about the gas exchange inside the alveoli, he mentioned the flow of air and the flow of blood was going in opposite directions so that there always would be a concentration difference.
Because of this the gas exchange between the alveolar space and capillary continues and reaches ~99%.
I could not understand how the air would always go in the same direction so I researched about the topic. All resources I found state that when the air enters the alveolus there is a pressure gradient for both oxygen and carbon dioxide between the capillary and the alveolar space.
But I found nothing mentioning the opposite direction of flow for air/blood.
So does that mean gas exchange for oxygen and carbon dioxide stop when diffusion equilibrium is reached?
(I'm not a native English speaker so I hope this question makes sense.)