What are alveoli?
The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. The gas-blood barrier between the alveolar space and the pulmonary capillaries is extremely thin, allowing for rapid gas exchange. To reach the blood, oxygen must diffuse through the alveolar epithelium, a thin interstitial space, and the capillary endothelium; CO2 follows the reverse course to reach the alveoli.
The alveoli are the final branchings of the respiratory tree and act as the primary gas exchange units of the lung. i hope this link helps http://oac.med.jhmi.
An alveolus (plural: alveoli), is an anatomical structure that has the form of a hollow cavity. 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 peculiar to mammalian lungs; different structures are involved in gas exchange in other vertebrates.[1] Location The alveoli are found in the respiratory zone of the lungs. Structure The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli. There are two major alveolar cell types in the alveolar wall (pneumocytes): * Type I cells that form the structure of an alveolar wall * Type II cells that secrete surfactant to lower the surface tension of water The alveoli have an innate tendency to collapse because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help
