Thorax Anatomy 1 Oko 2023 PDF

-Learning Objectives for Anatomy Lecture -Lecture : thorax - By the end of this section, you will be able to: • Discuss the components that make up the thoracic cage and vertebral column • Identify the parts of the sternum and define the sternal angle Dr.ali albassam MBBS .MSc .PhD 1 Thorax: ove...

-Learning Objectives for Anatomy Lecture -Lecture : thorax - By the end of this section, you will be able to: • Discuss the components that make up the thoracic cage and vertebral column • Identify the parts of the sternum and define the sternal angle Dr.ali albassam MBBS .MSc .PhD 1 Thorax: overview and surface anatomy • The thorax is the upper part of the trunk. • It consists of an external musculoskeletal cage, the thoracic wall, and an internal cavity that contains the heart, lungs, oesophagus, trachea, thymus, the vagus and phrenic nerves and the right and left sympathetic trunks, the thoracic duct and major systemic and pulmonary blood vessels. • Inferiorly the thorax broad thoracic outlet (inferior thoracic aperture) is separated from the abdominal cavity by the diaphragm, superiorly narrow thoracic inlet (superior thoracic aperture) typically measures 5.5-6 cm anterior-posteriorly and 10 cm transversely, it communicates with the neck and the upper limbs. The thoracic wall also offers protection to some of the abdominal viscera: the greater part of the liver lies under the right dome of the diaphragm; the stomach and spleen lie under the left dome of the diaphragm; the posterior aspects of the superior poles of the kidneys lie on the diaphragm and are anterior to the twelfth rib on the right, and to the eleventh and twelfth ribs on the left. 2 Variations in thoracic dimensions and proportions are partly deferent between individual and also linked to age, sex and race. At birth, the transverse diameter is relatively less than it is in the adult, but adult proportions develop as walking begins. Thoracic capacity is less in females than it is in males, both absolutely and proportionately: the female sternum is shorter, the thoracic inlet more oblique, and the suprasternal notch is level with the third thoracic vertebra (whereas it is level with the second in males). In all individuals, the size of the thoracic cavity changes continuously, according to the movements of the ribs and diaphragm during respiration, and the degree of distension of the abdominal viscera 3 The thoracic cage (rib cage) forms the thorax (chest) portion of the body. It consists of the 12 pairs of ribs with their costal cartilages and the sternum. The ribs are anchored posteriorly to the 12 thoracic vertebrae (T1–T12). The thoracic cage protects the heart and lungs. 4 The Bony Thorax 5 FUNCTIONS • Breathing • Protection of vital organs 6 Bony Thorax • Forms the framework of the chest • Components of the bony thorax • Thoracic vertebrae – posteriorly • Ribs – laterally • Sternum and costal cartilage – anteriorly • Protects thoracic organs • Supports shoulder girdle and upper limbs • Provides attachment sites for muscles 7 8 sternal angle (of Louis). 9 10 11 To remember: Sternal angle – 2nd pair of costal cartilages & ribs – IV disc of T4/T5 Superior Thoracic opening Manubrium Body of sternum Xiphoid Ribs – true 1 – 7 false 8 – 10 (floating 11-12) Thoracic vertebrae Inferior Thoracic opening *intercostal space – space between two ribs 12 13 14 15 Ribs 16 17 Rib I Most acutely curved and usually shortest, the first rib is broad and flat, its surfaces are superior and inferior, and its borders are internal and external . It slopes obliquely down and forwards to its sternal end. The obliquity of the first ribs accounts for the appearance of pulmonary and pleural apices in the neck. 18 Intervertebral Symphysis (secondary cartilaginous) Costotransverse Synovial plane joint Articulation of tubercle of rib with transverse process of corresponding vertebra. Costochondral Primary cartilaginous joint. Interchondral Synovial plane joint. Manubriosternal Secondary cartilaginous joint (symphysis). Xiphisternal Primary cartilaginous joint (synchondrosis) 19 20 21 Thoracic aperture The superior thoracic opening (thoracic inlet) communicates with the neck and upper extremities and is bounded by: 1. 1st Body of thoracic vertebra 2. 1st pair of ribs and their costal cartilages 3. jugular notch of the sternum The inferior thoracic opening (thoracic outlet) is closed by the diaphragm and is bounded by: 1. 12th thoracic vertebra 2. 11th and 12th pair of ribs 3. Costal cartilages of ribs 7th – 10th 4. Xiphisternal joint 22 Superficial muscles of anterior thoracic wall Pectoralis major Subclavius Pectoralis minor (covered by clavipectoral fascia) Serratus anterior 23 Intercostal spaces lie between adjacent ribs and are filled by intercostal muscles . Intercostal nerves and associated major arteries and veins lie in the costal groove along the inferior margin of the superior rib and pass in the plane between the inner two layers of muscles. In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Therefore, the nerve is the structure most at risk when objects perforate the upper aspect of an intercostal space. Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below. Deep to the intercostal spaces and ribs, and separating these structures from the underlying pleura, is a layer of loose connective tissue, called endothoracic fascia, which contains variable amounts of fat. Superficial to the spaces are deep fascia, superficial fascia, and skin. Muscles associated with the upper limbs and back overlie the spaces. 24 25 26 Muscles of the Thoracic Wall I. Superficial • External intercostal muscles II. Middle • Internal intercostal muscles III. Deep • • • • Innermost intercostal muscles Subcostal muscles Transversus thoracic muscles Levatores costarum 27 Intercostal spaces Intercostal spaces lie between adjacent ribs and are filled by intercostal muscles . In each space, the vein is the most superior structure and is therefore highest in the costal groove. The artery is inferior to the vein, and the nerve is inferior to the artery and often not protected by the groove. Small collateral branches of the major intercostal nerves and vessels are often present superior to the inferior rib below. 28 External intercostal muscles • External intercostal:• Superior attachment-Inferior margin of rib above. • Inferior attachment-Superior surface of rib below. • Function-Most active during inspiration; supports intercostal space; moves ribs superiorly. • Direction of the fibers of the external intercostal – medial and downward (like hands in the front pockets) • Prolongation of external fibers will form a letter X on your abdomen just like eXternal. • The eleven pairs External intercostal muscles Anterior or External intercostal Membrane (AIM) 29 30 31 External intercostal muscles and membrane 32 External intercostal muscles and membrane 33 Internal intercostal muscles • Superior attachmen-Lateral edge of costal groove of rib above. • Inferior attachment-Superior surface of rib below deep to the attachment of the related external intercostals. • Function-Most active during expiration; supports intercostal space; moves ribs inferiorly • Direction of the fibers of the internal oblique – lateral and upward (like hands in the back pockets) opposite to fibers of external intercostal muscles Posterior intercostal membrane (PIM) Internal intercostal muscles 34 35 36 Innermost intercostals Each muscle is attached to the internal aspects of two adjoining ribs. They are insignificant, and sometimes absent, at highest thoracic levels, but become progressively more substantial below this, extending through about the middle two quarters of the lower intercostal spaces. Posteriorly the innermost intercostals, in those spaces where they are well developed, may come together with the corresponding subcostales. The innermost intercostals are related internally to the endothoracic fascia and parietal pleura, and externally to the intercostal nerves and vessels Innervation 37 Serratus posterior superior Serratus posterior inferior 38 Subcostales Superior attachment- Internal surface (near angle) of lower ribs Inferior attachment- Internal surface of second or third rib below May -depress ribs. Transversus thoracis;Superior attachment- Lower margins and internal surfaces of costal cartilages of second to sixth ribs, Inferior attachment- Inferior aspect of deep surface of body of sternum, xiphoid process and costal cartilages ribs IV-VII. Depresses costal cartilages 39 40 Intercostal nerves  Ventral primary rami  Gives two branches • Lateral cutaneous branch • Anterior cutaneous branch  Function : sensory and motor innervation of the thoracic wall and upper abdomen also lateral limb of diaphragm (only sensory) and parietal pleura  Dermatome (skin) and myotome (muscles) – innervated by a single pair of spinal nerves. T12 intercostal nerve = Subcostal 41 Intercostal nerves Innervation of the thoracic wall is mainly by the intercostal nerves, which are the anterior rami of spinal nerves T1 to T11 and lie in the intercostal spaces between adjacent ribs. The anterior ramus of spinal nerve T12 (the subcostal nerve) is inferior to rib XII . A typical intercostal nerve passes laterally around the thoracic wall in an intercostal space. The largest of the branches is the lateral cutaneous branch, which pierces the lateral thoracic wall and divides into an anterior branch and a posterior branch that innervate the overlying skin. In addition to these major branches, small collateral branches can be found in the intercostal space running along the superior border of the lower rib. 42 In the thorax, the intercostal nerves carry: • somatic motor innervation to the muscles of the thoracic wall (intercostal, subcostal, and transversus thoracis muscles); • somatic sensory innervation from the skin and parietal pleura; and • postganglionic sympathetic fibers to the periphery. Sensory innervation from the skin overlying the upper thoracic wall is supplied by cutaneous branches (supraclavicular nerves), which descend from the cervical plexus in the neck. In addition to innervating the thoracic wall, intercostal nerves innervate other regions: • the anterior ramus of T1 contributes to the brachial plexus; • the lateral cutaneous branch of the second intercostal nerve (the intercostobrachial nerve) contributes to cutaneous innervation of the medial surface of the upper arm; • the lower intercostal nerves supply muscles, skin, and peritoneum of the abdominal wall. 43 Posterior cutaneous branch Dorsal primary ramus Intercostal nerve, Ventral primary ramus Lateral cutaneous branch Sympathetic trunk Anterior cutaneous branch 44 45 The neurovascular bundle (VAN) • • • • Vein – is located superiorly Artery – is between vein and nerve Nerve – is located inferiorly VAN occupies the costal groove (inferior edge of the rib) • VAN is situated between internal intercostal & innermost intercostal muscles Vein Artery Nerve 46 Herpes Zoster  Varicella Zoster virus – initial infection chickenpox  Lies dormant in the dorsal root ganglia  Reactivation along a ganglion’s distribution - shingles 47 48 Arterial supply Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces . 49 50 Anterior intercostal arteries • Internal thoracic artery ITA – branch of subclavian artery, runs on the internal surface of the thorax, laterally to sternum, anteriorly to pleura • ITA divides into the musculophrenic artery and superior epigastric artery • Two pairs of anterior intercostal arteries 51 After branching from the first part of the subclavian, the right and left internal thoracic arteries pass in an inferior direction into the thoracic cavity by coursing posterior to the subclavian vein and first rib. They continue on a vertical course through the thoracic cavity along the sides of the sternum. Along their path they form the following branches. • The pericardiaphrenic artery branches from the internal thoracic to course inferiorly between the pericardium and the pleura on a path alongside the phrenic nerve. It supplies the pericardium proximally and a small portion of the diaphragm distally. • Anterior intercostal arteries branch from the internal thoracic arteries as they cross the first 6 intercostal spaces. Anterior intercostal arteries transport blood to the anterior portion of the intercostal spaces to supply the intercostal muscles. In addition, branches pass through the intercostal muscles to supply the pectoral muscles, breast, and skin. Intercostal spaces 16 are supplied by branches directly from the internal thoracic artery. • At the level of the 6th intercostal space, the internal thoracic artery forms the following 52 terminal branches. • Musculophrenic a. • The musculophrenic artery continues inferiorly to cross the 7th-9th intercostal spaces, which it supplies by anterior intercostal arteries that branch from it. • The musculophrenic artery continues distally to contribute blood supply the anterolateral diaphragm. • Superior epigastric a. • The superior epigastric artery descends to the anterior abdominal wall to anastomose with the inferior epigastric artery (remember this from GI). The anastomosis between the two vessels occurs in the location between the posterior rectus sheath and the rectus abdominis muscle. 53 Arterial supply Vessels that supply the thoracic wall consist mainly of posterior and anterior intercostal arteries, which pass around the wall between adjacent ribs in intercostal spaces . These arteries originate from the aorta and internal thoracic arteries, which in turn arise from the subclavian arteries in the root of the neck. Together, the intercostal arteries form a basket-like pattern of vascular supply around the thoracic wall. Posterior intercostal arteries:- originate from vessels associated with the posterior thoracic wall. The upper two posterior intercostal arteries on each side are derived from the suprerior intercostal artery, which descends into the thorax as a branch of the costocervical trunk in the neck. The costocervical trunk is a posterior branch of the subclavian artery. The remaining nine pairs of posterior intercostal arteries arise from the posterior surface of the thoracic aorta. Because the aorta is on the left side of the vertebral column, those posterior intercostal vessels passing to the right side of the thoracic wall cross the midline anterior to the bodies of the vertebrae and therefore are longer than the corresponding vessels on the left. 54 anterior intercostal arteries:- originate directly or indirectly as lateral branches from the internal thoracic arteries. Each internal thoracic artery arises as a major branch of the subclavian artery in the neck. It passes anteriorly over the cervical dome of pleura and descends vertically through the superior thoracic aperture and along the deep aspect of the anterior thoracic wall. On each side, the internal thoracic artery lies posterior to the costal cartilages of the upper six ribs and about 1 cm lateral to the sternum. At approximately the level of the sixth intercostal space, it divides into two terminal branches: • the superior epigastric artery, which continues inferiorly into the anterior abdominal wall , • the musculophrenic artery, which passes along the costal margin, goes through the diaphragm, and ends near the last intercostal space. Anterior intercostal arteries that supply the upper six intercostal spaces arise as lateral branches from the internal thoracic artery, whereas those supplying the lower spaces arise from the musculophrenic artery. In each intercostal space, the anterior intercostal arteries usually have two branches: • one passes below the margin of the upper rib; • artery. the other passes above the margin of the lower rib and meets a collateral branch of the posterior intercostal 55 Summary of of Intercostal Vessels The blood supply to intercostal spaces varies by level. • Intercostal spaces 1-6 (Figure 1) • Anterior intercostal arteries directly branching from the internal thoracic artery • Posterior intercostal arteries • Posterior intercostal arteries 1 and 2 branch from the costocervical trunk, which branches from the second part of the subclavian artery (region of subclavian posterior to the anterior scalene muscle). • Posterior intercostal arteries 3-6 are branches from the thoracic aorta. • Intercostal spaces 7-9 (Figure 2) • Anterior intercostal arteries branching from the musculophrenic artery • Posterior intercostal arteries branching from the thoracic aorta • Intercostal spaces 10 and 11 (Figure 3) • Posterior intercostal arteries ONLY that branch from the thoracic aorta. 56 57 58 Venous drainage Venous drainage from the thoracic wall generally parallels the pattern of arterial supply . Centrally, the intercostal veins ultimately drain into the azygos system of veins or into internal thoracic veins, which connect with the brachiocephalic veins in the neck. Often the upper posterior intercostal veins on the left side come together and form the left superior intercostal vein, which empties into the left brachiocephalic vein. Similarly, the upper posterior intercostal veins on the right side may come together and form the right superior intercostal vein, which empties into the azygos vein 59 Lymphatic drainage Lymphatic vessels of the thoracic wall drain mainly into lymph nodes associated with the internal thoracic arteries (parasternal nodes), with the heads and necks of ribs (intercostal nodes), and with the diaphragm (diaphragmatic nodes) . Diaphragmatic nodes are posterior to the xiphoid and at sites where the phrenic nerves penetrate the diaphragm. They also occur in regions where the diaphragm is attached to the vertebral column. Parasternal nodes drain into bronchomediastinal trunks. Intercostal nodes in the upper thorax also drain into bronchomediastinal trunks, whereas intercostal nodes in the lower thorax drain into the thoracic duct. Nodes associated with the diaphragm interconnect with parasternal, prevertebral, juxta-esophageal nodes, brachiocephalic (anterior to the brachiocephalic veins in the superior mediastinum), and lateral aortic/lumbar nodes (in the abdomen). Superficial regions of the thoracic wall drain mainly into axillary lymph nodes in the axilla or parasternal nodes. 60 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 61 62 63