Library · Physiology
Gas exchange
Make it clearer
Gas exchange is the passage of gases between the air inside the alveolus, one of the little sacs where the airway ends, and the blood in the pulmonary capillaries. For it to work, two things have to happen at the same time: air has to move into and out of the alveolus, which is called ventilation, and blood has to reach it, which is called perfusion.
That crossing happens mainly by diffusion, that is, on its own. The gases cross the surfactant that coats the alveolus, the epithelium that lines it, the basement membrane and the endothelium of the capillary, all within a thin septum. Air on one side, blood on the other, and one wall the gases cross.
The relationship between ventilation and perfusion is called the V/Q ratio, ventilation over perfusion. When it is abnormal, it can contribute to hypoxemia, which means having too little oxygen in the blood.
In brief
Gas exchange takes place between alveolar air and pulmonary capillary blood, and it requires an alveolus that is ventilated and perfused.
It happens mainly by diffusion: the gases cross the surfactant, the alveolar epithelium, the basement membrane and the capillary endothelium of the septum.
Air on one side, blood on the other, and one wall the gases cross.
Ventilation is the flow of air into and out of the alveolus, and perfusion the flow of blood to its capillaries; an abnormal V/Q ratio can contribute to hypoxemia.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Pulmonary Ventilation and Perfusion, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated