BIOL 221 Lecture Notes - Lecture 7: Bronchiole, Elastic Fiber, Exhalation
3 Mar 2020
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Document Summary
Respiratory zone is where gas exchange occurs. The respiratory bronchioles have scattered alveoli in their walls. Respiratory bronchioles lead to alveolar ducts, alveolar sacs and alveoli. Alveolar ducts are passageways where alveoli open into them. Each ends in a cluster of alveoli called alveolar sacs. Alveoli (air sacs; singular = alveolus) are thin-walled structures in which gas exchange between air and blood takes place. Elastic fibers in the walls are important to compliance and elasticity of the lungs. Type i pneumocytes are simple squamous epithelial cells that function in gas exchange. Type ii pneumocytes are scattered cuboidal cells that secrete surfactants. Surfactants are composed of phospholipids and lipoproteins (have hydrophobic and hydrophilic regions) that decrease the surface tension of the thin layer of water on the inside of the alveoli. This is important to preventing collapse during exhalation. In order for gases to be exchanged between blood and air, they have to pass through the respiratory membrane.
