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(December 2007)| An alveolus (plural: alveoli, from Latin
alveolus, "little cavity") is an anatomical structure that has
the form of a hollow cavity. Found in the lung parenchyma, the
pulmonary alveoli are the terminal ends of the respiratory tree,
which outcrop from either alveolar sacs or alveolar ducts, which
are both sites of gas exchange with the blood as well. Alveoli
are particular to mammalian lungs. Different structures are
involved in gas exchange in other vertebrates. The alveolar
membrane is the gas-exchange surface. Carbon dioxide rich blood
is pumped from the rest of the body into the alveolar blood
vessels where, through diffusion, it releases its carbon dioxide
and absorbs oxygen. The alveoli are located in the respiratory
zone of the lungs, at the distal termination of the alveolar
ducts and atria. These air sacs are the forming and termination
point of the respiratory tract. They provide total surface area
of about 100 m2. The alveo