|Function||Exchange of oxygen and carbon-dioxide through the respiratory membrane|
|Alveolar cells||Type I pneumocyte (squamous alveolar cells with thin membrane; allow gas exchange) Type II pneumocyte (repair alveolar epithelium, secrete pulmonary surfactant) Alveolar macrophages|
There are three major types of alveolar cell. Two types are pneumocytes or pneumonocytes known as type I and type II cells found in the alveolar wall, and a large phagocytic cell known as an alveolar macrophage that moves about in the lumens of the alveoli, and in the connective tissue between them.
Type II cells are defenders of the alveoli by secreting surfactant, keeping the alveolar space relatively free from fluid, serving as progenitor cells to repopulate the epithelium after injury, and providing important components of the innate immune system.
Cells of the Alveoli
- Type I pneumocytes . These are the cells responsible for the exchange of oxygen and CO2.
- Type II pneumocytes. These cells perform two important functions. They produce surfactant , which helps keep the balloon shape from collapsing. They can also turn into type I cells in order to repair damage.
The alveolus is composed of alveolar epithelial type 1 cells, alveolar epithelial type 2 cells and capillary cells . Type 1 cells are large, squamous epithelial cells that cover ~95% of the alveolar surface area. Type 2 cells produce surfactant and play a role in maintenance of lung fluid balance.
broad, simple squamous epithelial cells that make up the majority of the cells lining the walls of the alveoli.
Two types are pneumocytes or pneumonocytes known as type I and type II cells found in the alveolar wall , and a large phagocytic cell known as an alveolar macrophage that moves about in the lumens of the alveoli, and in the connective tissue between them.
Compared to type 1 cells, type 2 cells are smaller . However, they are the most numerous cells in the alveoli. Type 2 pneumocytes can proliferate and differentiate into type 1 cells to compensate for damaged cell
Four major functions have been attributed to alveolar type II cells: (1) synthesis and secretion of surfactant ; (2) xenobiotic metabolism; (3) transepithelial movement of water; and (4) regeneration of the alveolar epithelium following lung injury.
The key difference between type 1 and type 2 pneumocytes is that type 1 pneumocytes are thin and flattened alveolar cells that are responsible for the gas exchange between alveoli and capillaries , while type 2 pneumocytes are cuboidal alveolar cells that are responsible for the secretion of pulmonary surfactants that .
The pulmonary alveolar epithelium is mainly composed of two types of epithelial cells: alveolar type I (AT1) and type II (AT2) cells . AT2 cells are smaller, cuboidal cells that are best known for their functions in synthesizing and secreting pulmonary surfactan