alveolus

Alveolus, plural alveoli, is a term used in anatomy to denote a small cavity or pit within a tissue or organ. The word derives from Latin and is applied in several distinct structures that share the basic idea of a hollow space.

In the respiratory system, the pulmonary alveolus (alveolus of the lung) is one of countless tiny air sacs at the ends of the respiratory tree. They are sites of gas exchange, with very thin walls formed by type I pneumocytes and surfactant-producing type II pneumocytes, and they are enveloped by a dense network of capillaries. The alveolar membrane allows oxygen to diffuse into the blood and carbon dioxide to diffuse out. The surface area of the alveoli is large, which facilitates efficient gas transfer, and alveolar macrophages patrol the air spaces to remove inhaled particles.

In dentistry and maxillofacial anatomy, the dental alveolus or alveolar socket is the bony cavity within the jaw that houses a tooth. The tooth is anchored by the periodontal ligament within the alveolar bone proper, a specialized bone lining the socket. The alveolar process of the maxilla and mandible forms the supporting bone around the teeth and undergoes remodeling during eruption, function, or tooth loss. Alveolar bone loss is a hallmark of periodontitis and can lead to tooth mobility and changes in bite.

Other related uses include alveolitis, referring to inflammation of an alveolus, such as the dry socket that can follow extraction.