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| Pulmonary Alveolus |
The alveolus is the gaseous exchange surfaces formed in the squamous epithelial cells of the lungs and rich in the caustic reticulum. These are the structural and functional units of the lung. The human lung contains more than 700 million alveoli across a surface area of about 70 to 90 square meters.
The wall of each alveolus is extremely thin. Only 0.1 micrometers whole. The caudal reticulum is formed from the pulmonary artery and then fully merges to form the pulmonary vein. Rough squamous epithelium formed. It also contains collagen and elastin fibers. This facilitates contraction and expansion during respiration. The wall of the alveolus contains phagocytic alveolar macrophages. Destroys foreign objects.
Some of the special cell walls of the alveolar wall secrete chemicals. The substance is called surfactant. The alveolus lowers the surface tension of the fluid in the wall, causing the lungs to contract and expand with less effort during respiration. The air and the alveolar wall help oxygen and carbon dioxide to get faster. It then destroys the incoming germs. 23 weeks of age means that the first surfactant secretion begins. For this reason, human embryos before 24 weeks are not considered to have an independent existence.
