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Mid-semester essay exam notes - Lungs

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R6.17: Lung The lung is the essential respiration organ. Human lungs are located in two cavities on either side of the heart, however they are not identical. Both lungs are separated into lobes by fissures, with 3 lobes on the right and 2 on the left. Each lobe is surrounded by a pleural cavity, which consists of 2 pleurae. The parietal pleura lies against the rib cage, and the visceral pleura lies on the surface of the lungs. In between the pleura is pleural fluid. The pleural cavity helps lubricate the lungs, as well as provide surface tension to keep the lung surface in contact with the rib cage. Their principle function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. A large surface area is needed for this exchange of gases which is accomplished by specialized cells that form thin-walled air sacs, alveoli. In humans, the trachea divides into the two main bronchi that enter the roots of the lungs. The bronchi continue to divide within the lung, and after multiple divisions, give rise to bronchioles. The bronchial tree continues to branch until its reaches the level of terminal bronchioles, which lead to alveolar sacs. Alveolar sacs are made up of clusters of alveoli, where the individual alveoli are tightly wrapped in blood vessels and it is here that gas exchange actually occurs. There are 4 stages in lung development: embryonic stage, pseudoglandular stage, canalicular stage, and terminal sac stage. Embryonic stage is where the developing lungs grow into and begin to fill the pleural cavities. Embryonic development starts at 4-7 weeks after conception. After 4 weeks, the gut tube of the primitive gut grooves into the anterior wall, and that groove goes deeper, so it forms a pouch at the front, which is derived from the endoderm. It can be said that the lung is developed from the gut. Pseudoglandu
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