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Type I cells, also called type I pneumocytes, or type I alveolar cells, are squamous, thin and flat and form the structure of the alveoli. Type II cells, also called type II pneumocytes or type II alveolar cells, release pulmonary surfactant to lower surface tension, and can also differentiate to replace damaged type I cells. [12] [15]
Micrograph showing hemosiderin-laden alveolar macrophages, as seen in a pulmonary hemorrhage. H&E stain.. An alveolar macrophage, pulmonary macrophage, (or dust cell) is a type of macrophage, a professional phagocyte, found in the airways and at the level of the alveoli in the lungs, but separated from their walls.
It exists to prevent air bubbles from forming in the blood, and from blood entering the alveoli. It is formed by the type I pneumocytes of the alveolar wall, the endothelial cells of the capillaries and the basement membrane between. The barrier is permeable to molecular oxygen, carbon dioxide, carbon monoxide and many other gases. [1]
Alveolar type II epithelial cells play the critical roles of producing surfactant, moving water out of the airspaces, and regenerating alveolar epithelium. [5] The alveolar type II epithelial cells are more resistant to damage, so after an insult to the alveoli, most of the damage will occur to the alveolar type I epithelial cells. [5]
The pores of Kohn (also known as interalveolar connections or alveolar pores) are discrete holes in walls of adjacent alveoli. [1] Cuboidal type II alveolar cells, which produce surfactant, usually form part of aperture. [2]
This type of alveolar damage can be attributed to nonconcentrated and nonlocalized alveoli damage, marked alveolar septal edema with inflammatory cell infiltration, fibroblast proliferation, occasional hyaline membranes, and thickening of the alveolar walls.
The two types of cell are known as type I and type II cells [32] (also known as pneumocytes). [3] Types I and II make up the walls and alveolar septa. Type I cells provide 95% of the surface area of each alveoli and are flat ("squamous"), and Type II cells generally cluster in the corners of the alveoli and have a cuboidal shape. [33]
Alveoli are the spherical outcroppings of the respiratory bronchioles. Pulmonary surfactant is a surface-active complex of phospholipids and proteins formed by type II alveolar cells. [1] The proteins and lipids that make up the surfactant have both hydrophilic and hydrophobic regions.