Syllabus: 6 pages (Page 6 lists corresponding figures for Grant's Atlas 11 th & 12 th Eds.)

Transcription

1 PLEURAL CAVITY AND LUNGS Dr. Milton M. Sholley SELF STUDY RESOURCES Essential Clinical Anatomy 3 rd ed. (ECA): pp Syllabus: 6 pages (Page 6 lists corresponding figures for Grant's Atlas 11 th & 12 th Eds.) Head to Toe Questions in Gross Anatomy: Continue questions # ; start # Structures: Parietal pleura costal, mediastinal, diaphragmatic, cervical or cupula innervated by intercostal nerves and phrenic nerves Visceral pleura over lung surface, pulmonary ligament Lung shape, surfaces, borders, fissures, lobes, root, hilum Trachea primary bronchi, lobar (2 o ) bronchi, segmental (3 o ) bronchi Vessels pulmonary artery and vein, pericardiacophrenic artery & vein. bronchial artery and vein (know the concept; difficult to find) Lymph nodes (know the concept and find a few; difficult to distinguish groups) pulmonary, bronchopulmonary, tracheobronchial, paratracheal I. Pleura and Pleural Cavities A. Boundaries of the Pleural Cavities: The two lungs, each with its pleural sac, are contained in the thoracic cavity. The pleura is a thin glistening, slippery serous membrane that covers the internal surface of the thoracic wall, to which it is attached, and in this location is called parietal pleura. It is reflected over the mediastinum and onto the lung, where it is then called visceral (or pulmonary) pleura. The visceral pleura covers the lung and dips into its fissures. The opposed surfaces of the parietal and visceral pleura slide smoothly against each other during respiration. The potential space between them is the pleural cavity, which contains a film of fluid of capillary thinness. B. Parietal pleura: Costal, Mediastinal, Diaphragmatic and Cervical (Cupula) 1. The costal pleura in front turns sharply onto the mediastinum where it becomes the mediastinal pleura. The edge of the reflection is called the anterior border of the pleura. The part of the pleural cavity between the layers of this pleural reflection is the costomediastinal recess. Inferiorly, the costal pleura is continuous with the diaphragmatic pleura, the costodiaphragmatic recess being created by its reflection. The edge of the recess, which is termed the inferior border of the pleura, usually does

2 not extend as far inferiorly as the costal attachments of the diaphragm. Posteriorly, the costal pleura turns forward over the side of the bodies of the vertebrae, and is again continuous with mediastinal pleura at its indefinite, broad posterior border. Please study Grant's Atlas 12 th Ed. Figure 1.26, which includes the figure below. Relationships of Lungs and Parietal Pleura to Ribs Anterior View Cupula of pleura Apex of lung Clavicle Rib 2 Rib 8 Margin of lung Rib 10 Margin of pleura The Sternal and Costal Reflections of the parietal pleura can be visualized with respect to the external chest wall by remembering the evennumbered ribs: 2, 4, 6, 8, 10 and 12. The right and left sternal reflections of pleura pass behind the sternoclavicular joints to meet each other at the sternal angle (2nd rib). The right reflection continues downward in the midline to the xiphoid process (Rib 6). The left reflection descends in the midline as far as Rib 4, where it diverges to the left (to make room for the heart), crossing the midposition of the 6th costal cartilage. (This leaves the bare area of the pericardium uncovered, allowing injection of the heart at this site without the needle going through the pleural sac). Both left and right reflections continue laterally, reaching the 8th Rib near the midclavicular line, cross the 10th Rib in the midaxillary line, and neck of the 12th Rib at the vertebral column. The posterior aspect of the costodiaphragmatic recess lies in relation to the kidney.

3 2. The mediastinal pleura covers the mediastinal or midline structures. At the root of the lung it turns laterally, enclosing the structures of the root and becoming continuous with visceral pleura. Inferior to the root of the lung, the mediastinal pleura forms a double layer between lung and esophagus and is termed the pulmonary ligament. The pleura of the right and left sides approach each other above the level of the arch of the aorta, behind the esophagus. Reflection of each side behind the esophagus forms a retroesophageal recess, and contributes to the retrocardiac space seen radiographically. The pericardiacophrenic vessels, which run in neurovascular bundles with the phrenic nerves on either side of the heart, supply blood to the mediastinal pleurae. 3. The diaphragmatic pleura covers the superior surface of the diaphragm except its central tendon, which is fused with the fibrous pericardium. Intercostal nerves are sensory to the periphery of the diaphragmatic pleura and the phrenic nerves are sensory to the larger, more central areas. 4. The cupula of the pleura (or cervical pleura) and apex of the lung are at the level of the 1st rib posteriorly. But the 1st rib slopes downward as it curves laterally and anteriorly. Hence, the lung and pleura project above the level of the anterior part of the rib and, therefore, above the superior thoracic aperature, into the root of the neck. 5. The parietal pleura is sensitive to pain, which is the somatic type carried in GSA pathways. The costal pleura, cervical pleura, and periphery of the diaphragmatic pleura receive sensory innervation from the intercostal nerves. The phrenic nerves mediate sensation from the mediastinal pleura and the large central areas of the diaphragmatic pleura. 6. In contrast to the parietal pleura, the visceral pleura is insensitive to pain. There are GVA fibers derived from the autonomic nerves within the lung, but these are not thought to mediate pain from the visceral pleura. II. The Lungs A. Structure 1. The structure of the right and left lungs is described in terms of shape, surfaces, borders (margins), lobes, fissures, and a root or hilum. Internally, the lung has air passages (bronchial tree), pulmonary arteries and veins and their branches, bronchial arteries and veins, and lymphatic nodes and vessels. 2. The shape of the lung is roughly conical, presenting a tapered upper end, the apex, and a broad base. Each lung has three surfaces, costal, diaphragmatic and medial, with borders or margins that demarcate one

4 from the other (anterior and inferior borders). All surfaces are covered by visceral pleura, which unites with the mediastinal pleura around the root of the lung. The root of the lung, containing blood vessels, nerves, lymphatics and bronchi, serves to attach the lung to the mediastinum. The entry area for these structures into the lung is the pulmonary hilum. Fissures divide the lung into lobes. Both lungs are divided into an upper and lower lobe by the oblique fissure, but only the upper lobe of the right lung is divided by a horizontal fissure to form an additional middle lobe. 3. The trachea divides to form two primary bronchi. In the right lung, the right primary bronchus divides into an upper lobe bronchus and an intermediate bronchus. The intermediate bronchus then divides into middle and lower lobe bronchi. Thus, three lobar bronchi are formed, corresponding with the three lobes of the right lung. In the left lung, the left primary bronchus divides to form an upper and a lower lobe bronchus, corresponding with the two lobes of the left lung. In the right lung, the right pulmonary artery passes beneath the right upper lobar bronchus (eparterial bronchus), but above the middle and lower bronchi (hyparterial bronchi). In the left lung, the pulmonary artery passes above the upper and lower bronchi which are both hyparterial bronchi (below the artery). Note that the lower part of the upper lobe of the left lung is the equivalent of the middle lobe of the right lung and is called the lingula. 4. Internally, in the lung substance, the primary bronchi divide to form secondary (or lobar) bronchi, which subdivide to form tertiary bronchi, so that about 10 such tertiary bronchi are formed. Similar division of the pulmonary artery and vein occurs so that each tertiary bronchus is accompanied by its own pulmonary artery in close proximity and a pulmonary vein in a more peripheral position. Many more subdivisions of the structures occur so that the small bronchioles end in alveolar air sacs and the arterioles and venules form capillaries, in close proximity to the air sacs, the site of gaseous exchange. Bronchial arteries and veins supply blood to non respiratory tissues of the lung. 5. By actual dissection it was found that each of the 10 tertiary bronchi gave rise to an independent unit, termed a bronchopulmonary segment and that each could be removed, if necessary, during surgery, while leaving other segments intact. At this time, it is not necessary to learn the names of the segments, but you may be required to do so in later years.

5 B. Lymphatic Drainage of the Lungs 1. Lymphatic vessels on the surface of the lung (deep plexus) can be seen as blackened intersecting lines due to the presence of inhaled dust and carbon particles. Lymph fluid from these plexi travel to pulmonary nodes, which are located in the substance of the lung and can be observed as blackened spots. From the pulmonary nodes lymph fluid travels to bronchopulmonary nodes, which are larger nodes located adjacent to the hilus and usually appear as blackened masses. The bronchopulmonary nodes are connected to tracheobronchial nodes (also usually blackened) by lymph channels or vessels which are present in the mediastinal connective tissue and are not visible. The tracheobronchial nodes empty into paratracheal nodes alongside the trachea. The paratracheal nodes on the left side eventually drain into the thoracic duct, which empties into the junction of the left subclavian and left internal jugular veins. The paratracheal nodes of the right side eventually drain into the right lymphatic duct, which empties into the junction of the right subclavian vein and right internal jugular vein. 2. Normally the lymph fluid of each of the three lobes of the right lung drain into nodes and lymph channels on the right side. Similarly the two lobes of the left lung empty lymph fluid into nodes and lymph channels on the left side. Due to anastomoses between left and right channels, it has been found that occasionally the lingula and lower left lobe drain into the right side nodes and channels. In some cases lower left lobe tumors can be detected in the right scalene nodes in the neck, due to metastatic migration of the tumor cells. C. Mechanism of Respiration 1. Inspiration is flow of air into the lungs. Expiration is flow of air out of the lungs. Relaxed breathing is termed quiet respiration. Strenuous breathing is termed forced respiration. 2. In inspiration the dimensions (hence, the volume) of the thoracic cavity increase in the vertical, lateral and anterior posterior directions. The vertical dimension is increased by contraction of the diaphragm (diaphragmatic breathing). The lateral dimension is increased by contraction of the diaphragm on the sides of the lower ribs (7 10), as well as the contraction of the corresponding intercostal muscles. The anteriorposterior direction increases due to obliquity of the upper six ribs and contraction of corresponding intercostal muscles (thoracic breathing). 3. Expiration is usually a passive process and occurs because of the elastic recoil of the lungs and costal cartilages.

6 4. During forced breathing other muscles become involved. In forced expiration the abdominal muscles, including the internal and external obliques and transversus, contract. The scalene and sternoideidomastoid muscles in the neck aid in forced inspiration. Other muscles also may become involved. Figures from Grant's Atlas of Anatomy (11 th ed.) 1.23, page , page A,B&C, page A,B&C, page , page A&B, page C&D, page A&B, page , page , page , page , page , page , page , page , page , page 71 Figures from Grant's Atlas of Anatomy (12 th ed.) 1.23, page , page A,B&C, page A,B&C, page , page A&B, page C&D, page A&B, page , page , page , page , page A, page , page , page , page , page 73