Lung Alveolus Structure - Lung Alveoli Anatomy
Respiratory Membrane and Gas Exchange
In the lungs, gas exchange takes place in the alveolar sacs. Oxygen (O2) diffuses from the alveoli into the capillaries and RBCs. At the same time, carbon dioxide (CO2) in the capillaries diffuses into the alveoli.
- The bonding of O2 to hemoglobin in the RBCs causes their color to change from purple to red. See the GIF below
- During the exchange, the gases must rapidly cross the respiratory membrane that separates the alveolar and capillary lumens.
- The respiratory membrane is about 0.6 micrometers thick and consists of the alveolar squamous cell, the capillary endothelial cell, and two fused basement membranes (formed by the alveolar and capillary cells).