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Measurements of lung volume obtained during the controlled inflation/deflation of a normal lung show that the volumes obtained during deflation exceed those during inflation, at a given pressure. This difference in inflation and deflation volumes at a given pressure is called hysteresis and is due to the air-water surface tension that occurs at ...
When this mixture contacts water, for example, it accumulates at the water-air interface and forms a thin superficial pellicule of surfactant. The polar heads of the molecules composing the surfactant are attracted by the polar molecules of the liquid (in this case, H 2 O molecules), causing a significant diminution of the water's surface tension.
The lungs expand and contract during the breathing cycle, drawing air in and out of the lungs. The volume of air moved in or out of the lungs under normal resting circumstances (the resting tidal volume of about 500 ml), and volumes moved during maximally forced inhalation and maximally forced exhalation are measured in humans by spirometry. [12]
The fluid coating is produced by the body in order to facilitate the transfer of gases between blood and alveolar air, and the type II cells are typically found at the blood–air barrier. [19] [20] Type II cells start to develop at about 26 weeks of gestation, secreting small amounts of surfactant.
The respiratory airway secretory cell (RAS), is found in the lungs of humans and some other mammals, notably ferrets. They are facultative progenitors that have important functional roles in maintaining lung airway health. Their role in maintaining the gas-exchange compartment of the lung is critical and they may be altered in chronic lung disease.
Another important cell type is the pulmonary neuroendocrine cell. These are innervated cells that only make up around 0.5% of the respiratory epithelial cells. [7] The ciliated cells are columnar epithelial cells with specialized ciliary modifications. The ciliated cells make up between 50 and 80 per cent of the epithelium. [8]
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 skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialized cells. While the lungs are of primary importance to breathing control, the unique properties of cutaneous respiration supplements rapid gas exchange when amphibians are submerged in oxygen-rich water. [7]