Anatomic Region Located B/W Lungs Described As a Divider Separating Two Pleural Cavities

Mediastinum (Baptista #1) 21:04

Mediastinum anatomic region located b/w lungs described as a divider separating two pleural cavities corridor thru which head & neck region structures connect w/ lower regions of body & vice versa contains all principal tissues & organ of chest EXCEPT lungs Landmarks Superior thoracic aperture connects neck w/ mediastinum manubriosternal joint (sternal angle) bump exists in front of 2nd rib costocartilage union w/ sternum/manubrium landmark for cardiac valves @ 4th-5th vertebral body levels inferior thoracic aperture Boundaries extends from sternum back to VC Laterally pericardium (membrane enclosing heart) mediastinal pleurae (membranes that are continues w/ those lining thoracic cage) Division of the thoracic cavity contains heart thymus gland portions of esophagus portions of trachea anatomical compartments NOTE: T4-T5 is division b/w superior & inferior mediastinum superior above manubriosternal angle posterior boundary is first 4 thoracic vertebrae superior mediastinum continuous w/ neck continuous below w/ anterior & posterior mediastinum (NOT middle) laterally -- limited by parietal (mediastinal) pleura Contents thymus 1° lymphoid organ lower part of neck anterior part of superior mediastinum (lies posterior to manubrium) extends into anterior mediastinum continues to grow & after puberty it gradually involutes & is replaced by fat aortic arch brachiocephalic trunk L. common carotid a. L. SCA Superior Vena Cava (SVC) L & R brachiocephalic vv. Trachea L & R bronchi Esophagus R vagus nerve L vagus nerve L recurrent laryngeal nerve Phrenic nn. Thoracic duct inferior (below T4/5 vertebral level) anterior ventrally -- sternum posteriorly -- pericardial sac contents sternopericardial ligament (fatty) fat lymph nodes middle ventrally -- anterior mediastinal compartment dorsally -- posterior mediastinal compartment contents pericardium heart phrenic nn. pericardacophrenic vesses stems of great vessels posterior anteriorly -- pericardial sac (middle compartment) posteriorly -- anterior surface of vertebral bodies contents descending aorta esophagus azygos system of vv. vagus n. thoracic duct lymph nodes thoracic splanchnic nn. Most pathologies occurred in anterior inferior compartment of mediastinum (41/102) CLINICAL: Wide mediastinum width > 6cm (on upright chest x-ray) commonly caused by aneurysmal aortic arch, where the sac of aorta blooms due to weakness of pericardial wall at that spot Internal thoracic artery descends into thorax 1.2 cm lateral to edge of sternum ends @ 6th rib costal cartilage, divides into musculophrenic a. (supplies diaphragm) superior epigastric a. (supplies anterior abdominal wall) NOTE: cardiac bypass uses this artery in surgery Aorta Ascending Aorta -- from L ventricle to aortic arch mostly w/in pericardial sac Aortic Arch -- above plan of manubriosternal angle courses posterolaterally (left side of body) Major branches brachiocephalic superiorly & to right of trachea divides into R SCA R common carotid a. L common carotid a. superior & anterior to trachea anterior to L SCA L subclavian a. superior to trachea & esophagus lies against left lung & pleura Descending Aorta -- thoracic aorta continuation of arch on L side of vertebrae moves downward toward midline **reaches midline @ T12 as it passes thru diaphragm Major branches R & L bronchial aa. posterior intercostal aa. esophageal branches mediastinal branches Pulmonary Trunk & Arteries trunk courses upward & to the left divides into pulmonary aa. under concave aortic arch take deoxygenated blood from heart to lungs L pulmonary a. anterior to descending aorta *ligamentum arteriosum once ductus arteriosus (during fetal DEVO) connecting pulmonary a. to proximal descending aorta, allows most of blood from right ventricle to bypass fetus's fluid-filled non-functioning lungs. Upon closure @ birth, it becomes ligamentum arteriosum R pulmonary a. posterior to ascending aorta Great Veins of Thorax Inferior Vena Cava (IVC) **pierces diaphragm @ T8 vertebral level immediately enters pericardium & heart Left Brachiocephalic v. formed by joining of internal jugular v. & L SCV runs obliquely to right in front of great aa. & joins R brachiocephalic v. behind **intercostal space 1 forms superior vena cava Right brachiocephalic v. forms from joining of internal jugular v. & R SCV courses vertically behind manubrium forms SVC w/ L brachiocephalic Superior Vena Cava formed behind intercostal space 1 by both brachiocephalics runs vertically to Right Atrium receives Azygos vein Pulmonary vv. directly from root of lung to Left atrium give oxy-O2 back to heart Lymphatics Thoracic Duct Origin  cysterna chili ascends thru aortic hiatus of diaphragm ascends b/w azygos v. & aorta **LANDMARK: crosses to left side @ T4-T5 level to ascend behind esophagus joins confluence of internal jugular vv. & empties into L. subclavian v. Function drains all of body below diaphragm & left side of thorax (~3/4 of body) Right Lymphatic Duct right jugular drains right side of head & neck right subclavian drains right UL (ultimate drainage route) Bronchomediastinal drains right side of thorax Lymph Node Structure 4 afferent lymphatic vessels coming into node 2 efferent lymphatic vessels going out of node **maintains pressure inside Germinal follicles where B-cells proliferate Medullary sinuses macrophages are here lymph runs thru here before going out efferent filters or traps for foreign particles, immune system Anterior mediastinal nodes near great vessels in superior mediastinum afferents: thymus, pericardium, pleura, heart efferents: join retrosternal & tracheobronchial to form bronchomediastinal trunk Middle mediastinal Nodes tracheobronchial bifurcation (carinal) bronchopulmonary Posterior mediastinal Nodes near esophagus & aorta afferents: mediastinal viscera efferents: thoracic duct Trachea tube connecting pharynx & larynx to lungs & allows passage of air esophagus is posterior ascending aorta is anterior carina -- bifurcates @ T4-5** (common landmark) Esophagus courses thru superior & posterior mediastinum continues superiorly w/ pharynx in neck **pierces diaphragm @ T10 level to join stomach upper portion in thorax is slightly left of center lower portion passes thru diaphragm to left of midline pushed toward midline by aortic arch muscular tube striated mm. in neck smooth mm. in lower 1/3 mixed in middle Associations anteriorly trachea left bronchus pericardium (left atrium) posteriorly vertebral bodies thoracic duct azygos system intercostal aa. right side terminal azygos left side aortic arch Constrictions superior end in neck (junction of esophagus w/ pharynx) where aorta & left bronchus compress it near gastric end (esophageal hiatus) Arteries esophageal branches of thoracic aorta anastomose w/ inferior thyroid aa & left gastric aa. Veins submucosal plexus & surface plexus drain to azygos system may drain superiorly to inferior thyroid vv. may drain inferiorly to gastric v. Innervation striated muscle vagal (recurrent branch) smooth muscle parasympathetic vagal esophageal plexus surrounds lower thoracic esophagus mostly vagal fibers some sympathetic Nerves -- Mediastinum phrenic nerve right phrenic descends along R side great veins brachiocephalic v. SVC right atrium IVC anterior to root of lung left phrenic courses along left side of subclavian a. crosses left side of aortic arch anterior to root of lung along left side of pericardial sac vagus nerve “wandering” preganglionic PARASYMPATHETIC fibers for thoracic & abdominal viscera right vagus enters thorax posterolateral to brachiocephalic vein anterior to right SCA right recurrent branch hooks under SCA to ascend hear trachea & esophagus descends to lateral side of trachea  posterior to root of lung descends on posterior esophagus to form plexus passes thru diaphragm w/ esophagus as posterior vagal trunk left vagus enters thorax b/w carotid & SCA descends to cross left side of aortic arch recurrent branch recurves around ligamentum arteriosum to ascend in neck b/w trachea & esophagus behind root of lung (for left & right vagus) anterior esophagus  forms plexus thru diaphragm as anterior vagal trunk branches in thorax left recurrent laryngeal branch to pulmonary plexus branch to esophagus branch to cardiac plexus Azygos System of Veins (azygos, hemiazygos, accessory hemiazygos, left superior intercostal) Azygos vein **terminates into SVC @ level of sternal angle (T4-T5 level) runs up RIGHT SIDE of thoracic vertebral column branches esophageal mediastinal pericardial bronchial Hemiazygos vein branches off to left side of thorax around T9 travels inferiorly, ½ length of azygos on left side of midline Accessory Hemiazygos branches off to left side of thorax around T8 runs on upper left side of midline Left superior intercostal vein **only independent branch drain 2nd, 3rd & 4th intercostal spaces passes posteriorly to aortic arch 21:04 21:04