Lungs and Pleura PDF Anatomy Notes

Anatomy 534 Lungs and Pleura 212 The Thoracic Cavity The thoracic inlet is bounded by the manubrium, R1 and its costal cartilage and T1 posteriorly. The thoracic outlet is inferior and surrounded by T12, the costal margin and the xip...

Anatomy 534 Lungs and Pleura 212 The Thoracic Cavity The thoracic inlet is bounded by the manubrium, R1 and its costal cartilage and T1 posteriorly. The thoracic outlet is inferior and surrounded by T12, the costal margin and the xiphisternal joint. The thoracic outlet is closed by the muscular diaphragm. 1 The thoracic cavity is bounded by the thoracic wall (sternum, 12 pairs of ribs and vertebral column), diaphragm, and superiorly the suprapleural membrane - a layer of fascia arching over each lung and extending up into the thoracic inlet. Within the thoracic cavity, a central mass (mediastinum) separates two pleural cavities. The Pleural Cavities The pleural cavities surround each lung. They are lined by serous membrane (pleura) but the cavity itself remains empty. The lung bud grows into a serous sac and becomes completely enveloped except at the point where the lung is anchored to the mediastinum. The pleura on the surface of the lung is the visceral pleura. That on the body wall is called parietal pleura. collapsed tiff illiik.si The Pleura The parietal pleura lines the inside of the thoracic wall, separated from the musculature by the endothoracic fascia. It has a number of specialized divisions - based on that portion of the thoracic cavity it is found lining: w min in back - costal pleura - lines the back side of the thoracic (rib) cage firstpaired - mediastinal pleura - lines the mediastinal mass If - diaphragmatic pleura - lines the diaphragm - cervical pleura (cupola) - pleura that covers the apex of the lungs within the thoracic inlet - lining the inside of the reinforcing suprapleural membrane  Anatomy 534 Lungs and Pleura 213 Lungs in Coronal Section an fifiY E f Iftikhar in thought pm closed pwam diaphragmatic pleura The parietal pleura reflects off the mediastinum onto the surface of the lung, as visceral pleura, at the 1 itp root of the lung. The parietal pleura sags below the root (like the cuff on a shirt) forming an unfilled potential space. This double layer of pleura is referred to as the pulmonary ligament E n aft The visceral pleural is intimately attached to the surface of the lung it and cannot be lifted to demonstrate. It dives deep into the fissures of the lung before reflecting upon onto the adjacent lobe. The costal pleura is innervated by the intercostal nerves of the intercostal space. The diaphragmatic pleura is Medial Aspect of the Right Lung innervated by the intercostal nerves peripherally and the sensory component of the phrenic nerve centrally. These membranes are highly sensitive to pain. The visceral pleura is not innervated and is thus insensitive to pain Anatomy 534 Lungs and Pleura 214 Pleural Recesses These are areas where the parietal pleura reflects off one aspect of the thoracic cavity onto another, forming potential spaces or recesses. These recesses are never completely filled by the lung The costomediastinal recess is formed by the reflection of the mediastinal pleural off the media- stinum onto the costal wall - forming a vertical strap-like recess on either side of the sternum. The costodiaphragmatic recess is formed by the reflection of the diaphragmatic pleura off the diaphragm onto the costal wall - forming a semicircular recess that communicates with the costomediastinal recess anteriorly and passing posteriorly to meet the vertebral column. mediastinal pinna y into Fp c recess Costilava X-Section Through Root of the Lung The Suprapleural Membranes i compartmeal Iii The entire thorax is lined by endothoracic fascia that functions in adhering the parietal pleura to the various aspects of the body wall, mediastinum and diaphragm. The thoracic inlet (operculum) is located at the the root of the neck and is bounded by the first ribs, the vertebral column and the manubrium. The endothoracic fascia extends across Anatomy 534 Lungs and Pleura these openings and thickens into the suprapleural membranes. These membranes cover the superior (apical) portion of each lung. The “Holey Ghost” of the Thorax: (a “negative pressure” in a potential space). i i During expiration, the elastic tension of the tracheobronchial tree tends to pull the lung and its adherent visceral pleura 7 away from the parietal pleural- lined walls of the thoracic cavity. This creates a “negative pressure” within the pleural sac. The pleural sac contains only a few milliliters (ml.) of serous fluid and is therefore a potential space. The negative pressure within this potential space (between the two pleural layers) is 5 cm. H20 lower than atmospheric pressure. However, atmospheric pressure within the alveoli presses the lung and its adherent visceral pleura against the parietal pleura, with the fluid-filled potential pleural cavity in between. This situation is similar to licking (wetting) a suction-cup and pressing it against a piece of glass. You can move the suction cup all over the surface of the glass (if you put enough fluid in the cup) but you cannot remove the suction cup from the glass. If either the visceral or parietal pleura is punctured (ie. spontaneous rupture of the visceral pleura as seen in emphysema or a puncture-type wound from a sharp object through the thoracic wall and underlying parietal pleura) the elastic recoil of the tracheobronchial trees sucks air into the pleural cavity (sac). The two pleural surfaces separate and the lung “collapses”. This scenario is referred to clinically as a pneumothorax. Efforts to re-establish the workability of the lung during respiration involve redevelopment of the negative pressure. The tear/puncture must be closed. Once this is done a tube is left exiting the pleural cavity with the collapsed lung. The tube passes into a bottle of water placed lower than the lung so that expired air from the pleural sac cannot re-enter nor can fluid flow into the lung. Eventually, the atmospheric air is expelled from the lung, the two pleural surfaces again re- contact one another and negative pressure is re-established. The tube is quickly withdrawn and the opening closed. Anatomy 534 Lungs and Pleura 216 Surface Anatomy of the Lungs 2 n M for A E Anatomy 534 Lungs and Pleura 217 Lobes of the Lungs and the Pleural Recesses The diagrams on the next page illustrate the extent of two pleural-lined potential spaces within each pleural sac - the costodiaphragmatic and costomediastinal pleural recesses. These potential pleural-lined spaces accept the sharp inferior and anterior borders of the lungs during inspiration. Fluid may also accumulate in these spaces and knowledge of their extent is important for its aspiration. In this series of diagrams, note the extent of each lobe of the lung on the Is anterior/posterior/lateral aspects of the body. Knowledge of this is important for listening to breath sounds in the various lobes of the lung. is Anatomy 534 Lungs and Pleura 218 Root (Hilum) of the Lungs Each root is surrounded by the reflection of parietal pleura onto the surface of the lung as visceral pleura. This pleural reflection extends inferiorly into the pulmonary ligament. Pulmonary vv., pulmonary aa., bronchi, and broncho- pulmonary lymph nodes are found in the cut surface of each root. Bronchial aa. supply oxygen-laden blood to the lung tissue, as branches Iii directly off the aorta. Bronchial vv. drain carbon dioxide-laden blood from the lung tissue into the azygous system. Relationship Between the Pulmonary Vessels and the Tracheo-bronchial Tree The pulmonary aa. lie above the bronchi except for the secondary bronchus to the right upper lobe. The pulmonary vv. lie below the bronchi. Pulmonary aa. follow the bronchi all the way to the level of their termination as alveoli. The alveoli are drained by intersegmental pulmonary vv. which diverge from the bronchi. These veins extend through the intersegmental connective tissue septa. They eventually coalesce and rejoin the tracheo-bronchial tree at the level of the Anatomy 534 Lungs and Pleura 219 tertiary bronchi. The veins are often used as surgical guidelines for resection of a broncho- pulmonary segment. Bronchi The trachea bifurcates at the sternal angle (T4/5) into two main bronchi. The right main bronchus is short and diverges little from the trachea - the primary reason that most inhaled objects end up in this bronchus. The left main bronchus is longer than the right and more horizontal, leaving the trachea at a distinct angle. Within the substance of the lung each main bronchis divides into secondary bronchi (supplying a lobe of the lung). In turn these divide into tertiary bronchi that supply an individual portion of each lobe, known as a bronchopulmonary segment (BPS). A BPS is the smallest resectable portion of the lung and is supplied by a tertiary bronchus. Each lung contains 10 BPSs (the left lung utilizes an upper and lower division with 4 quaternary bronchi to get 10). Their location is important with reference to positioning the body for draining regions of the lung by percussion (postural drainage). air Trachec divideslung carina ftp.wn.in 1 iEEE so 10 Bronchus supplies lung 2 Bronchus supplies lobe 3 Bronchi supply bronchopulmonary segment BPS 4 91 1 stable Anatomy 534 Lungs and Pleura 220 Within each BPS the bronchi eventually get narrower until they form bronchioles that continue on to take inhaled/exhaled air to the respiratory units of the lung - the alveoli. The diagrams below outline the position of the various BPS in each lung. Clinically (radiolo- gically) - and in the lab - the pattern of the bronchial tree is more important as they are demon- strable on x-ray. Surgically, a knowledge of the position and extent of the actual BPS is important. Right Lung FYI Left Lung 10 BPS Upper lobe: Upper lobe: 1 - Apical (3o) Upper division (3o) 2 - Posterior (3o) Either 1 - Apical (4o) 3 - Anterior (3o) Middle lobe: IN 2 - Posterior (4o) 3 - Anterior (4o) 4 - Lateral (3o) luns Lower division (3o) 5 - Medial (3o) 4 - Superior (lingual) (4o) Lower lobe: 5 - Inferior (lingual) (4o) 6 - Superior (3o) Lower lobe: 7 - Medial basal (3o) 6 - Superior (3o) 8 - Anterior basal (3o) 7 - Medial basal (3o) 9 - Lateral basal (3o) 8 - Anterior basal (3o) o 10 - Posterior basal (3 ) 9 - Lateral basal (3o) 10 - Posterior basal (3o) We had made W Anatomy 534 Lungs and Pleura 221 Nerve Supply smooth mug ones 1 Lung tissue is supplied by sympathetic and parasympathetic fibers from the anterior and posterior pulmonary plexuses that lie anterior to and posterior to the roots of the lungs. The smooth muscle of the bronchioles, blood vessels and mucous membrane are innervated by these fibers. Parasympathetic stimuli cause the smooth muscle of the bronchioles to constrict, sympathetic fibers will relax (dilate) these tubes. Lymphatic Drainage Lung cancer incidence places importance on lymphatic drainage. A superficial lymphatic plexus lies just under the visceral pleura. A deep plexus follows the bronchial tree. They both meet at the hilus of the lung where they drain into the bronchopulmonary group of nodes at the root of the lung. From here the lymph passes through the tracheobronchial and paratracheal nodes and eventually into the venous system via the thoracic or right lymphatic ducts that enter the subclavian vv. FYI Superficial Pulmonary Lymphatics Deep Pulmonary Lymphatics