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Gas exchange in the alveolus. Type I cells are the larger of the two cell types; they are thin, flat epithelial lining cells (membranous pneumocytes), that form the structure of the alveoli. [3] They are squamous (giving more surface area to each cell) and have long cytoplasmic extensions that cover more than 95% of the alveolar surface. [12] [17]
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] Left side demonstrate the structure of a normal alveolus including the difference between type I and type II alveolar epithelial cells.
Surfactant is a surface-active lipoprotein complex formed by type II alveolar cells. The proteins and lipids that comprise surfactant have both a hydrophilic region and a hydrophobic region. By absorbing to the air-water interface of alveoli with the hydrophilic head groups in the water and the hydrophobic tails facing towards the air, the main ...
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.
The red blood cells also carry carbon dioxide (CO 2) away from the cells in the form of carbaminohemoglobin and release it into the alveoli through the alveolar capillaries. When the diaphragm relaxes, a positive pressure is generated in the thorax and air rushes out of the alveoli expelling the carbon dioxide.
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]
An alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood.
The surface tension acts at the air-water interface and tends to make the bubble smaller (by decreasing the surface area of the interface). The gas pressure (P) needed to keep an equilibrium between the collapsing force of surface tension (γ) and the expanding force of gas in an alveolus of radius r is expressed by the Young–Laplace equation: