Anatomy of the Mediastinum PDF

Mediastinum • Mediastinum ‣ Contains all thoracic viscera except lungs ‣ Air or liquid make this viscera a highly mobile area ‣ Superior and inferior divisions • Mediastinum extends: ‣ Superiorly: thoracic aperture ‣ Inferiorly : Diaphragm ‣ Anteriorly: Sternum and costal cartilages ‣ Posteriorly: T...

Mediastinum • Mediastinum ‣ Contains all thoracic viscera except lungs ‣ Air or liquid make this viscera a highly mobile area ‣ Superior and inferior divisions • Mediastinum extends: ‣ Superiorly: thoracic aperture ‣ Inferiorly : Diaphragm ‣ Anteriorly: Sternum and costal cartilages ‣ Posteriorly: T4-T5 thoracic vertebrae Thorax Pleural Cavity Medistanum Superior Inferior Ant Mid Post • Superior Mediastinum ‣ Thoracic aperture to the sternal angle (ant) and the IV disc between T4 and T5 ‣ Contents: • Great vessel of heart • Arch of the aorta and its branches • Vagus • Phrenic nerves • Cardiac plexus • Laryngeal nerve • Trachea • Esophagus • Thoracic duct • Thymus gland • Inferior Mediastinum: ‣ Anterior Mediastinum ◦ Sternopericardial ◦ Ligaments ◦ fat ◦ lymph nodes/ vessels In infants the anterior mediastinum contains the inferior part of the thymus. ‣ Middle Mediastinum (center of sternal angle to floor of diaphragm) ◦ SVC ◦ Ascending aorta ◦ Pulmonary trunk ◦ Arch of azygous vein ◦ Main bronchi ◦ pericardium and the heart contained within pericardium ‣ Posteriror Mediastinum (from IV disc between T4- T5 to floor of diaphragm.) ◦ Contains thoracic aorta ◦ Thoracic duct ◦ azygous and hemiazygous vein ◦ thoracic sympathetic vein ‣ Layers of the heart: Pericardium Fibrous Serous Parietal (outer) Visceral (inner layer of heart) ◦ Made of two layers: ‣ Fibrous pericardium - outermost &.tough) anchors/ protect heart ◦ Continuous with central tendon of the diaphragm ‣ Serous pericardium - deep - two divisions • Parietal serous layer • Visceral serous layer ◦ Continuous with epicardium (outermost layer of the heart wall) • Pericardial cavity - between fibrous and serous pericardium ◦ contains serous fluid ◦ Fluid - minimizes friction when heart is beating ‣ Epicardium = outermost layer of heart wall ‣ Myocardium - middle layer of heart wall • Cardiac muscle that carries out cardiac contractions ‣ Endocardium - innermost layer of the heart wall • continuous with the tunica intima of the great vessels • Heart Arterial Supply ‣ Arterial supply mainly from the pericardiacophrenic artery (branching off from interal thoracic artery) ‣ Smaller blood contribution from musculophrenic artery (terminal branch from internal thoracic artery), bronchial, esophageal, and superior phrenic artery from thoracic aorta. • Venous drainage supply ‣ Primarily: Pericardiacophrenic veins ‣ Variable tributaries: azygous venous system • Pericardium Nerve Supply: ‣ Phrenic nerves- C3 - C5 • Pain sensations from these nerves are referred to the skin of the ipsilateral shoulder region. ‣ Sympathetic trunks - vasomotor. ‣ Trasnverse pericardial sinus • Located anterior to the SVC and post to aorta and pulmonary trunk • The heart ‣ Orientation: oblique plane with base toward right shoulder and apex toward left hip ‣ 2/3 of heart on left side ‣ Pushes left making left lung smaller ‣ KNOW BORDER AND SURFACES OF HEART • Chambers of heart ‣ Right and left atrium ‣ Right and left ventricle • Right atria ‣ Right auricle - small muscular area increase volume capacity of R atrium ‣ Where deoxygenated blood return to the heart ‣ Vessels converging w/ R atria: • SVC • IVC Vessels drain into sinus venarum • Coronary sinus ‣ Interatrial septum - separates L and R atria ‣ Makes a thumbprint like depression - oval fossa ‣ Right atrioventricular orifice ‣ Opening where blood passes from R Atrium => Tricuspid => R. Ventricle ‣ Tricuspid valve guards this orifice • Tricuspid has 3 cusps • Chordae tendineae- structures that attach papillary muscles ◦ Allows passage of blood when open ◦ Prevent back flow when closed ‣ Pectinate muscles make up contractile part of the wall ‣ Right ventricle • Irregular muscular elevations => trabeculae carneae • Diastole - fills with blood • Systole - pumps blood to pulm arteries => lungs ‣ Pulmonary valve • between right ventricle and pulm trunk • allow passage of blood during systole • closes during dyastole and allows right ventricular filling. ‣ Interventricular septum • Separates right and left ventricle • Made up of muscle, fibrous skeleton of the heart, and carries atrioventricular bundles, bundle branches, and ultimately right bundle branch. • Carried to right ventricle by the septomarginal trabecula. ‣ Blood flow: • Blood leave R ventricle (systole) => pulmonary valve => pulmonary trunk => R/L pulm arteries => alveolar capillary system => intersegmental veins => superior/ inferior pulmonary veins => left atria • Left atria has slightly thicker wall than right atria ‣ Pectinae muscle ‣ atrioventricular orifice w/ fibrous ring => mitral (bicuspid valve) and chorda tendinae attached to papillary muscle extending from endocardium • The Heart ‣ Smooth outflow track, the aortic vestibule ‣ Has aortic orifice leading to ascending aorta ‣ Contains aortic valve, blood travels through it during systole ◦ Perfuses viscera/ extremeties with O2 blood ◦ Valves create aortic sinus (right, left, and posterior sinus) ◦ Coronary vessels deliver blood during dyastole ◦ Blood enters right and left coronary artery during dyastole ‣ More blood in sinus during dyastole. ‣ Coronary arteries branch off the right and left sinuses at the proximal end of ascending aorta. ◦ Serve to provide heart itself with oxygenated blood • Right Coronary Arteries (RCA) ‣ Right coronary - runs along coronary sulcus => Ascending branch (supplies SA node for 60 % of population) ‣ RCA => also gives off descending marginal branch (supplies right border of heart) ‣ RCA continues along sulcus and around the junction of all four chambers • Gives rise to atrioventricular nodal branch • Supplies AV node in 80% of population ‣ RCA => gives off interventricular branch (supplying both ventricles) ‣ From posterior Interventricular branch come small interventricular septal branches supplying IV septum ‣ RCA supplies R atria, most of R Ventricle, some left ventricles, and IV Septum (posterior 1/3). • Left Coronary Arteries (LCA) ‣ Travels along the left end of coronary sulcus. ‣ Gives off anterior interventricular branch and a circumflex ‣ Anterior interventricular branch supplies both ventricles as it travels to the apex of heart. • It then turns around the inferior border of the heart and anastomoses with the posterior IV branch of IV branch of the RCA • In many individuals the anterior IV artery gives rise to a lateral diagonal branch which descends the anterior surface of the heart. ‣ Circumflex branch - smaller • Travels posterior to the heart and forms left marginal artery supplying L ventricle ‣ Generally: LCA supplies Left atrium, most of L vent, most of IV septum, some of R Ventricle, SA node in some 40% of population • Venous drainage ‣ Venous drainage of the heart primarily from coronary sinus. ‣ Receives the great cardiac vein from the left ‣ Middle and small cardiac veins at its right ‣ Left posterior ventricular and marginal veins also drain into the coronary sinus. ‣ Small anterior cardiac veins from the R ventricular myocardium drain directly into the right atrium • Conducting system: ‣ Specialized fibers for initiating impulses and conducting them through the heart ‣ SA node • Pacemaker of the heart. • initiates and regulates impulses for contraction of the four chambers • Located just beneath epicardium, at junction of SVC and right atrium ‣ AV node • Located posteroinferior region of interatrial septum near opening of coronary simus, just above tricuspid valve. • Signal generated by SA node ◦ Passes through the wall of R atrium by the cardia muscle (myogenic conduction) ◦ This send signal rapidly to the AV node • AV node => AV bundles (through IV septum) => R and L bundle branches => subendocardial branches (purkinje fibers) • Right subendocardial branches travel through the septomarginal trabeculato stimulate the right papillary muscle and R ventricle • Left subendocardial branches stimulate the L papillary muscle and L ventricle • R/L subendocardial branches innervate the muscle of the IV septum. • Timing function of AV node delays the cardiac impulse for 0.1 sec • This is to allow completion of atrial contraction before ventricles contract • Cardiac innervation ‣ Autonomic nerve fibers from deep and superficial cardiac plexuses ‣ Sympathetic supply - from inferior cervical and superior T1-T5/T6 branches from the sympathetic trunk. ‣ Active during periods of intense activities "Fight of Flight" ‣ Increase heart rate, contractile force, BP, dilation of coronary A ‣ Parasympathetic supply - branches of CN X ‣ Rest and digest ‣ Slower heart rate, decrease BP, dec contractile force, constriction of coronary arteries. ‣ Both sympathetic fibers end in the SA and AV nodes.