Thoracic Cavity Lecture Notes PDF

-Learning Objectives for Anatomy Lecture -Lecture : Thoracic cavity Dr.Ali Albassam MBBS .MSc .PhD 1 Diaphragm • Closes inferior thoracic aperture – septum between thoracic and abdominal cavity • Major muscle of respiration * C3,4,5 – keeps the diaphragm alive 2 diaphragm The diaphragm is a c...

-Learning Objectives for Anatomy Lecture -Lecture : Thoracic cavity Dr.Ali Albassam MBBS .MSc .PhD 1 Diaphragm • Closes inferior thoracic aperture – septum between thoracic and abdominal cavity • Major muscle of respiration * C3,4,5 – keeps the diaphragm alive 2 diaphragm The diaphragm is a curved musculo fibrous sheet that separates the thoracic from the abdominal cavity. Its mainly convex upper surface faces the thorax, and its concave inferior surface is directed towards the abdomen. Major muscle of respiration. It is attached peripherally to the:  xiphoid process of the sternum;  costal margin of the thoracic wall;  ends of ribs XI and XII; ligaments that span across structures of the posterior abdominal wall; and vertebrae of the lumbar region. by crura of the diaphragm 3 is a double-domed musculotendinous structure that forms a physical boundary between the thoracic cavity and the abdominal cavity at the inferior thoracic aperture. Clinically, the diaphragm is often described as consisting of two halves (right and left hemidiaphragm) that are separated by an imaginary midsagittal plane. Each hemidiaphragm is dome-shaped where it projects superiorly toward the thorax. The level of the domes is altered during respiration, postural changes, and degree of abdominal viscera distention • The dome of the right hemidiaphragm projects superiorly slightly more than the left due to the large right lobe of the liver pushing it superiorly. At complete normal expiration in a standing person, the dome of the right hemidiaphragm is approximately at the position of the 5th rib anteriorly. • The dome of the left hemidiaphragm is at the level of the inferior border of the 5th rib at the midclavicular line. Note: The level of the fifth rib at the midclavicular line corresponds with the T8 vertebral level. 4 The crura are strong tendons attached to the anterolateral surfaces of the bodies of the upper lumbar vertebrae.  The right crus is fixed to the upper three lumbar vertebrae and the intervening discs.  the left crus likewise to the upper two lumbar vertebrae. Muscle fibres radiate from each crus, overlap, and pass vertically upwards before curving forwards into the central tendon 5 Diaphragm Apertures From these peripheral attachments, muscle fibers converge to join the central tendon. The pericardium is attached to the middle part of the central tendon.  Structures traveling between the thorax and abdomen pass through the diaphragm or between the diaphragm and its peripheral attachments:  the inferior vena cava passes through the central tendon at approximately vertebral level TVIII;  The esophagus and vagal trunks pass through the esophageal hiatus at vertebral level T10 (British spelling of oesophagus consists 10 letters).  the vagus nerves pass through the diaphragm with the esophagus;  the aorta passes behind the posterior attachment of the diaphragm at vertebral level TXII;  the thoracic duct passes behind the diaphragm with the aorta; 6 Diaphragm Apertures 7  the azygos and hemiazygos veins may also pass through the aortic hiatus or through the crura of the diaphragm.  Other structures outside the posterior attachments of the diaphragm lateral to the aortic hiatus include the sympathetic trunks and the least splanchnic nerves.  The greater and lesser splanchnic nerves penetrate the crura. 8 Arterial supply Arterial supply pericardiacophrenic and musculophrenic arteries supply the diaphragm. These vessels are branches of the internal thoracic arteries. Superior phrenic arteries, which arise directly from lower parts of the thoracic aorta, and small branches from intercostal arteries contribute to the supply. The largest arteries supplying the diaphragm arise from below it. These arteries are the inferior phrenic arteries, which branch directly from the abdominal aorta. 9 Venous drainage Venous drainage of the diaphragm is by veins that generally parallel the arteries. The veins drain into: the brachiocephalic veins in the neck; the azygos system of veins; or abdominal veins (left suprarenal vein and inferior vena cava). Innervation The diaphragm is innervated by the phrenic nerves (C3 to C5), which penetrate the diaphragm and innervate it from its abdominal surface. Contraction of the domes of the diaphragm flattens the diaphragm, so increasing thoracic volume. Movements of the diaphragm are essential for normal breathing. 10 Diaphragm has 2 portions: • Peripheral - muscular part (sternal, costal, lumbar) • Central - aponeurotic – central tendon Right leaflet of central tendon Middle leaflet of central tendon (fused with Left leaflet of central tendon pericardium) 11 Actions The major role of the diaphragm is inspiratory, but it is used also in abdominal straining.  Inspiration. When the fibers contract in tranquil inspiration only the domes descend; this sucks down the lung bases and does not disturb the mediastinum.  As the diaphragm contracts intra-abdominal pressure tends to rise, and the vena caval foramen (in the central tendon) is pulled widely open to assist venous return via the inferior vena cava.  The oesophageal opening is held closed by the pinch-like action resulting from contraction of the muscle sling of the right crus, to discourage regurgitation of stomach contents. The aortic opening is unaffected.  Abdominal straining. For evacuation of a pelvic effluent (defecation, micturition, parturition) diaphragmatic contraction aids that of the abdominal wall in raising intra-abdominal pressure  Hiccup is a (repeated) spasmodic contraction of the diaphragm, its contraction being followed immediately by closure of the glottis and subsequent release of the trapped air to produce the characteristic sound. 12 Associated with a lifetime of constant activity, about 55% of diaphragmatic muscle fibres (and 65% of intercostal muscle fibres) are of the slow twitch fatigue rsistant variety. Slow-twitch muscle fibers have high concentrations of mitochondria and myoglobin. Although they are smaller than the fast-twitch fibers, they are surrounded by more capillaries .This combination supports aerobic metabolism and fatigue resistance, particularly important for prolonged submaximal (aerobic) exercise activities. 13 14 15 -Learning Objectives for Anatomy Lecture -Lecture : Thoracic cavity and Viscera Dr.Ali Albassam MBBS .MSc .PhD 16 Thoracic cavity and Viscera 17 Thoracic cavity Thoracic cavity contains: • Two pulmonary cavities (right and left lung) • Mediastinum (between pulmonary cavities – all other structures) 18 A 54-year-old man who had smoked two packs of cigarettes per day for 20 years complains of the acute onset of shortness of breath, and severe chest pain with respiratory movement. On physical examination, he has a barrel chest consistent with chronic obstructive pulmonary disease. There are decreased breath sounds on the right side. When the physician taps on the right chest (percussion), there is a hyperresonant (unusually hollow) sound. • ◆ What is the most likely diagnosis? • ◆ What is the anatomical disorder? 19 ◆ Most likely diagnosis: Pneumothorax ◆ Anatomical disorder: Entry of air into the pleural space, resulting in lung collapse. • Objectives • 1. Be able to describe the contents of the pulmonary cavities: lungs and • the pleural divisions. • 2. Be able to describe the superior and inferior limits of the pleural cavity • and the lower limits of each lung. • 3. Be able to describe the functional importance of the pleural cavity and • fluid and the pressure within the cavity. 20 Thoracic cavity contains: • Two pulmonary cavities (right and left lung) • Mediastinum (between pulmonary cavities – all other structures)  superiorly, they extend above rib I into the root of the neck;  inferiorly, they extend to a level just above the costal margin;  the medial wall of each pleural cavity is the mediastinum 21 Pleurais a serous membrane which surrounds the lung (Bursa like fluid bags) single layer of flat cells, mesothelium, and an associated layer of supporting connective tissue; together, they form the pleura. continuous closed system has two layers • visceral pleura – invests the lungs (adherent to organ ) • parietal pleura – covers the internal surface of thoracic wall (away from organ) 22 23 The pleural sac can be visualized like a fist pushed into an inflated balloon, where your fist is representing the lung. In this "balloon analogy," the outer surface of the balloon not touching your fist represents the parietal pleura . The surface of the balloon in contact with your fist is the visceral pleura, and the air/space between these two surfaces represents the pleural cavity. Your wrist represents the root of the lung, where these two layers are continuous. 24 The pleura is divided into two major types, based on location: The names given to the parietal pleura correspond to the parts of the wall with which they are associate. •pleura related to the ribs and intercostal spaces is termed the costal part; •pleura covering the diaphragm is the diaphragmatic part. •pleura covering the mediastinum is the mediastinal part; •the dome-shaped layer of parietal pleura lining the cervical extension of the pleural cavity is cervical pleura (dome of pleura or pleural cupola). 25 Heart & Lungs In Situ R. Lung L. Lung Fibrous pericardium Parietal Pleura Visceral pleura (on lungs) Heart Pleural Sac 26 Cervical pleura visceral pleura Mediastinal pleura parietal pleura Costal pleura lungs Diaphragmatic pleura 27 Peripheral reflections Superiorly, the pleural cavity can project as much as 3-4 cm above the first costal cartilage, but does not extend above the neck of rib I. Anteriorly, the pleural cavities approach each other posterior to the upper part of the sternum. However, posterior to the lower part of the sternum, the parietal pleura does not come as close to the midline on the left side as it does on the right because the middle mediastinum, containing the pericardium and heart, bulges to the left. 28 Inferiorly, the costal pleura reflects onto the diaphragm above the costal margin. In the midclavicular line, the pleural cavity extends inferiorly to approximately rib 8. In the midaxillary line, it extends to rib10. From this point, →the inferior margin courses somewhat horizontally,→ crossing ribs 11 and 12 to reach vertebra T12 . From the midclavicular line to the vertebral column, the inferior boundary of the pleura can be approximated by a line that runs between the rib VIII, rib X, and vertebra TXII. 29 30 31 32 Pleural Cavity • Potential space between visceral and parietal pleura • Normally contents only a thin film of serous fluid Pleural recess – is a potential space where two adjacent parietal pleura are in contact (during expiration) and fill with lungs during deep inspiration. Pleural recess are : • Costodiaphragamtic • Costomediastinal • 33 Costodiaphragmatic recess Between costal pleura and diaphragmatic pleura 34 Costomediastinal recess Between costal pleura and mediastinal pleura 35 36 37 38 39 Innervation of pleura The parietal pleura is supplied by the • intercostal nerves (costal and cervical pleura), • phrenic nerves (mediastinal and central diaphragmatic pleura) and the • lower five or six intercostal nerves (peripheral diaphragmatic pleura). The visceral pleura is insensitive to pain WHY IS IT CLINICALLY IMPORTANT? 40 41 Pneumothorax The presence of air in the pleural cavity. Cause : • stab wound or broken rib damaging the parietal pleura or • more commonly in a spontaneous pneumothorax due to a little bulla of the lung bursting and tearing the visceral pleura. *mediastinal shift 43 Pneumothorax 44 45 Pleural fluid • Hemothorax is the accumulation of blood within the pleural cavity • result of trauma such as a stab wound or fractured rib but can also be due to lung disease. •Pleuritis accumulation of inflammatory exudate within the pleura cavity •The pain is referred from the parietal pleura to the cutaneous distribution of the intercostal nerve. 46 Thoracocentesis • remove excess fluid or to take a sample of fluid. • insert the needle along the superior border of the rib (VAN – inferior edge of rib) • 6th intercostal space in mid-axillary line 47 VAN External intercostal Internal intercostal Visceral pleura RIB Superficial thoracic muscle Pleural cavity Deep fascia LUNG RIB skin Superficial fascia Endothorasic fascia Innermost intercostal Parietal pleura 48 49 50 VAN External intercostal Internal intercostal Visceral pleura RIB Superficial thoracic muscle Pleural cavity Deep fascia LUNG RIB skin Superficial fascia Endothorasic fascia Innermost intercostal Parietal pleura 51 LUNGS The lungs are the essential organs of respiration. They are situated on either side of the heart and other mediastinal contents. At birth the lungs are pink, but in adults they are dark grey and patchily mottled. The adult right lung usually weighs c.625 g, and the left 565 g, but they vary greatly. Their weight also depends on the amount of blood or serous fluid contained within them. In proportion to body stature, the lungs are heavier in men than in women. 52 PULMONARY SURFACE FEATURES Each lung has a half-cone shape, with a base, apex, two surfaces and three borders. The base sits on the diaphragm. The apex projects above rib I and into the root of the neck. The two surfaces-the costal surface lies immediately adjacent to the ribs and intercostal spaces of the thoracic wall. The mediastinal surface lies against the mediastinum anteriorly and the vertebral column posteriorly and contains the comma-shaped hilum of the lung through which structures enter and leave. The three borders-the inferior border of the lung is sharp and separates the base from the costal surface. 53 Right lung The right lung has three lobes and two fissures . Normally, the lobes are freely movable against each other because they are separated, almost to the hilum, by invaginations of visceral pleura. These invaginations form the fissures:  the oblique fissure separates the inferior lobe (lower lobe) from the superior lobe and the middle lobe of the right lung;  the horizontal fissure separates the superior lobe (upper lobe) from the middle lobe The approximate position of the oblique fissure on a patient, in quiet respiration, can be marked by a curved line on the thoracic wall that begins roughly at the spinous process of vertebra TIV level of the spine, crosses the fifth interspace laterally, and then follows the contour of rib VI anteriorly . The horizontal fissure follows the fourth intercostal space from the sternum until it meets the oblique fissure as it crosses rib V. 54 The medial surface of the right lung lies adjacent to a number of important structures in the mediastinum and the root of the neck .These include the: heart, inferior vena cava, superior vena cava, azygos vein, and esophagus. The right subclavian artery and vein arch over and are related to the superior lobe of the right lung as they pass over the dome of cervical pleura and into the axilla. 55 right lung The medial surface of the right lung lies adjacent to a number of important structures in the mediastinum and the root of the neck . These include: the heart, inferior vena cava, superior vena cava, azygos vein, esophagus. 56 Left lung is smaller than the right lung and has two lobes separated by an oblique fissure . The oblique fissure of the left lung is slightly more oblique than the corresponding fissure of the right lung. During quiet respiration, the approximate position of the left oblique fissure can be marked by a curved line on the thoracic wall that begins between the spinous processes of vertebrae TIII and TIV, crosses the fifth interspace laterally, and follows the contour of rib VI anteriorly. The medial surface of the left lung lies adjacent to a number of important structures in the mediastinum and root of the neck .These include the: • heart, • aortic arch, • thoracic aorta, and esophagus. The left subclavian artery and vein arch over and are related to the superior lobe of the left lung as they pass over the dome of cervical pleura and into the axilla. 57 58 R Lung Fissures (Lateral view) L Upper Upper Middle Horizontal fissure Lower Lower Oblique fissure 59 60 left lung The left lung is smaller than the right lung The medial surface of the left lung lies adjacent to a number of important structures in the mediastinum and root of the neck . These include: the heart, aortic arch, thoracic aorta, esophagus. 61 Hilum of L & R Lungs L. lung Apex R. lung Primary Bronchus Pulmonary Artery ? Pulmonary Vein Pulmonary ligament 62 Within each root and located in the hilum are: a pulmonary artery; two pulmonary veins; a main bronchus; bronchial vessels; nerves; and lymphatics. 63 Bronchial tree Each main bronchus enters the root of a lung and passes through the hilum into the lung itself. The right main bronchus is wider and takes a more vertical course through the root and hilum than the left main bronchus . Therefore, inhaled foreign bodies tend to lodge more frequently on the right side than on the left. The main bronchus divides within the lung into lobar bronchi (secondary bronchi), each of which supplies a lobe. On the right side, the lobar bronchus to the superior lobe originates within the root of the lung. The lobar bronchi further divide into segmental bronchi (tertiary bronchi), which supply bronchopulmonary segments . Within each bronchopulmonary segment, the segmental bronchi give rise to multiple generations of divisions and, ultimately, to bronchioles, which further subdivide and supply the respiratory surfaces. 64 The walls of the bronchi are held open by discontinuous elongated plates of cartilage, but these are not present in bronchioles. Bronchopulmonary segments A bronchopulmonary segment is the area of lung supplied by a segmental bronchus and its accompanying pulmonary artery branch. Tributaries of the pulmonary vein tend to pass intersegmentally between and around the margins of segments. Each bronchopulmonary segment is shaped like an irregular cone with the apex at the origin of the segmental bronchus and the base projected peripherally onto the surface of the lung. A bronchopulmonary segment is the smallest, functionally independent region of a lung and the smallest area of lung that can be isolated and removed without affecting adjacent regions. There are ten bronchopulmonary segments in each lung 65 left right Trachea Main (1o bronchus) Upper Upper Lobar 20 bronchi Lower Lobar (2o bronchi) Middle Segmental (3o bronchi) Lower Segmental (3o bronchi) Carina 66 67 68 • The right main bronchus is wider and takes a more vertical course through the root and hilum than the left main bronchus . • Therefore, inhaled foreign bodies tend to lodge more frequently on the right side than on the left. 69 70 71 72 R L Bronchopulmonary segments Upper - Apex towards lung - Own arterial supply - Surgically resectable Upper Middle Lower Lower 73 74 75 76 Lungs 1º Bronchial Tree Lobes 2º Bronchopulmonary segments 3º 1º 1º R. Lung L. Lung •3 Lobes •10 BP segs •2 Lobes •10 BP segs fused to 8 77 VASCULAR SUPPLY AND LYMPHATIC DRAINAGE The lungs have two functionally distinct circulatory pathways. These are the pulmonary vessels, which convey deoxygenated blood to the alveolar walls and drain oxygenated blood back to the left side of the heart, and the much smaller bronchial vessels, which are derived from the systemic circulation and provide oxygenated blood to lung tissues which do not have close access to atmospheric oxygen, e.g. those of the bronchi and larger bronchioles 78 Pulmonary arteries The right and left pulmonary arteries originate from the pulmonary trunk and carry deoxygenated blood to the lungs from the right ventricle of the heart . The bifurcation of the pulmonary trunk occurs to the left of the midline just inferior to vertebral level TIV/V, and anteroinferiorly to the left of the bifurcation of the trachea. Right pulmonary artery The right pulmonary artery is longer than the left and passes horizontally across the mediastinum . It passes: anteriorly and slightly inferiorly to the tracheal bifurcation and anteriorly to the right main bronchus; and posteriorly to the ascending aorta, superior vena cava, and upper right pulmonary vein. 79 The right pulmonary artery enters the root of the lung and gives off a large branch to the superior lobe of the lung. The main vessel continues through the hilum of the lung, gives off a second (recurrent) branch to the superior lobe, and then divides to supply the middle and inferior lobes. Left pulmonary artery The left pulmonary artery is shorter than the right and lies anterior to the descending aorta and posterior to the superior pulmonary vein . It passes through the root and hilum and branches within the lung. 80 Pulmonary veins On each side a superior pulmonary vein and an inferior pulmonary vein carry oxygenated blood from the lungs back to the heart . The veins begin at the hilum of the lung, pass through the root of the lung, and immediately drain into the left atrium. Bronchial arteries and veins The bronchial arteries . and veins constitute the "nutritive" vascular system of the pulmonary tissues (bronchial walls and glands, walls of large vessels, and visceral pleura). They interconnect within the lung with branches of the pulmonary arteries and veins. The bronchial arteries originate from the thoracic aorta or one of its branches: • a single right bronchial artery normally arises from the third posterior intercostal artery (but occasionally, it originates from the upper left bronchial artery); • two left bronchial arteries arise directly from the anterior surface of the thoracic aorta-the superior left bronchial artery arises at vertebral level TV, and the inferior one inferior to the left bronchus. 81 Innervation The visceral pleura and other structures of the lung are supplied by visceral afferents and efferents distributed through the anterior pulmonary plexus and posterior pulmonary plexus . These interconnected plexuses lie anteriorly and posteriorly to the tracheal bifurcation and main bronchi. Branches of these plexuses, which ultimately originate from the sympathetic trunks and vagus nerves, are distributed along branches of the airway and vessels. Visceral efferents from: the vagus nerves constrict the bronchioles; the sympathetic system dilate the bronchioles. 82 Right lymphatic duct Thoracic duct Bronchomediastinal trunk Paratracheal nodes Superior and inferior tracheobronchial nodes Bronchopulmonary or hilar nodes 83 Lymphatic Drainage of Lungs • Intrapulmonary vessels & nodes  • bronchopulmonary (hilar) nodes  • tracheobronchial (carinal) nodes  • paratracheal nodes  • bronchomediastinal lymph trunk  • right thoracic trunk/thoracic duct  • systemic venous system 84 Lymphatic drainage Superficial, or subpleural, and deep lymphatics of the lung drain into lymph nodes called tracheobronchial nodes around the roots of lobar and main bronchi and along the sides of the trachea . As a group, these lymph nodes extend from within the lung, through the hilum and root, and into the posterior mediastinum. Efferent vessels from these nodes pass superiorly along the trachea to unite with similar vessels from parasternal nodes and brachiocephalic nodes, which are anterior to brachiocephalic veins in the superior mediastinum, to form the right and left bronchomediastinal trunks. These trunks drain directly into deep veins at the base of the neck, or may drain into the right lymphatic trunk or thoracic duct. 85