An alveolus (plural: alveoli, from Latin alveolus, "little cavity")'s an anatomical structure that's the form of a hollow cavity. Found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates. Location The alveoli are found in the respiratory zone of the lungs, providing a total surface ar… (More on Alveoli)