THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Each small tube ends in clusters of thin-walled air sacs, called alveoli. It is the alveoli that receive the oxygen and pass it on to the blood. The alveoli are surrounded by tiny blood vessels, called capillaries.

Detailed explanation-2: -The alveoli form clusters, called alveolar sacs, that resemble bunches of grapes. By the same analogy, the alveolar ducts leading to the sacs are like the stems of individual grapes, but, unlike grapes, the alveolar sacs are pocketlike structures made up of several individual alveoli.

Detailed explanation-3: -The alveolar membrane is the gas exchange surface, surrounded by a network of capillaries.