Clinical Module Summary Notes - Respiratory

Clinical Module Summary Notes - Respiratory - Dr. Glen...

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Revised 05/07/2009 The Respiratory System        The Pulmonary System Anatomy The lungs are divided into three lobes on right, and two on the left. Each of these lobes is subdivided into individual segments (10 for the right lung, 8 for the left lung) each having its own arterial, venous, lymphatic, and bronchial supplies. Adults have almost 300 billion (10 9 ) pulmonary arterioles which are the right diameter to be occluded by the MAA particles used in our studies (20 - 40 micron range). It is important to note that these are not the same arterioles as those derived from the bronchial arteries which supply blood to nourish the lung parenchyma. Remember that the lungs have two separate blood supplies, one to provide a circulation for gas exchange (the pulmonary circulation), and the other to maintain the cells which form the lungs (the bronchial circulation). The adult or mature number of pulmonary alveoli and arterioles is not reached until a child has reached 8 years of age or so (recent studies have indicated that children exposed to cigarette smoke may never develop this number). The number found in neonates is significantly lower but increases rapidly for the first twelve months, and progresses more slowly until 8. Clearly the physiology and anatomy is sufficiently different in children to require us to reduce the total number of MAA particles used in their studies (this is a separate concern from activity injected and will be discussed later). Airways divide from a single trachea which bifurcates (splits/divides) into a left and right bronchus, which in turn split into secondary -- or segmental -- bronchi, terminal bronchioles, alveolar ducts, and alveolar sacs or alveoli. In the airways cartilage is used to provide support to the trachea, and to progressively lesser degrees to all the structures down to the level of the bronchioles. Structures distal to the bronchioles receive their support from smooth muscle only and have no cartilage in their walls (this gives them greater flexibility). Neighboring alveoli are connected by small openings called the Pores of Kohn. These openings are important as they allow collateral passage of air into alveoli which lie distal to airway obstructions (this flow is achieved through "drifting" of gases). This collateral flow prevents atelectasis (the collapse of a lung or portion of it including its blood vessels) from occurring, and explains the delayed arrival, and retention of xenon in diseased areas of the lungs during ventilation studies in patients with COPD (Chronic Obstructive Pulmonary Disease). Alveoli (note these are not the same as arterioles!!) typically number about 300 million (10 6 ) in adults, or about one alveolus per 1,000 arterioles. Think of the alveolus as being a small The importance of understanding the anatomy of these segments lies in the fact that since a pulmonary embolism occurs when the supplying artery or one or more of the branches within a segment is (are) occluded
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Clinical Module Summary Notes - Respiratory - Dr. Glen...

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