Alveoli

Alveoli is the exact place where the gas exchange takes place. The structure consists of air space, surfactant, and alveoli fluid wrapped around the pulmonary arteriole and valve, transporting oxygenated and deoxygenated blood inside and out of alveoli. Alveoli are described as a round shaped-pocket of air. Due to the presence of surfactant serving as a structural support layer, the alveoli do not collapse.

A group of small spheres tight together where each one of them is labeled as alveoli. There is a zoom inside the alveoli, where only an empty air space and a small layer of surfactant are present.

Figure 1. Illustration of an alveoli.

Referred from:

Article

Structure of the respiratory system

Article

Intrapleural pressure