What is the primary site for an exchange of gases in the lungs?

Concept: An alveolus is made up of a simple squamous epithelial layer and an extracellular matrix surrounded by capillaries. The epithelial lining is a component of the alveolar membrane, also known as the respiratory membrane, which permits gaseous exchange.

The primary site for the exchange of gases in our body is alveoli. 

There are 300 million of alveoli in both lungs. 

These have thin walls consisting of squamous epithelium with a network of blood capillaries.