HUBS Week 9 - Thorax: Mediastinum & Heart Anatomy

Thorax Borders and Surface Anatomy

  • Borders/Walls: Vertebrae, 12 ribs, manubrium, sternebrae & xiphoid, intercostal muscles.

  • Thoracic Inlet: First rib, T1T_1, and manubrium.

  • Thoracic Outlet: Costal margin, filled by diaphragm.

Mediastinum Divisions and Contents

  • Four Divisions: Superior, Middle, Anterior, Posterior.

    • Superior Mediastinum: Contains great vessels (Aorta, Brachiocephalic artery, Left common carotid artery, Left subclavian artery, Superior vena cava).

    • Anterior Mediastinum: Smallest subdivision; contains internal thoracic/mammary arteries and thymus (up to T<em>IV/T</em>VT<em>{IV}/T</em>V vertebral level).

    • Posterior Mediastinum: Contains Aorta and branches, Esophagus, Thoracic duct, Azygous venous system, and Sympathetic plexus/chain.

    • Middle Mediastinum: Contains the heart.

Azygos Venous System

  • Unusual drainage system for the chest wall, on the right side.

  • Clinical Importance: Capable of returning blood from the lower body to the heart if the Inferior Vena Cava (IVC) is blocked.

  • Veins: Azygos vein (main), Hemiazygos vein, Accessory hemiazygos vein.

Thoracic Duct

  • Major lymphatic vessel, located in the posterior mediastinum.

  • Collects lymph from most of the body.

Sympathetic Chain

  • Part of the sympathetic nervous system.

  • Located in the posterior mediastinum, forming plexuses throughout thoracic/abdominal cavities.

Heart Position and Pericardium

  • Position: Cone-shaped, with apex pointing inferolaterally (around left 5th5^{th} intercostal space).

  • Pericardial Sac: Encloses heart and roots of great vessels.

    • Layers: Outer fibrous and inner serous (visceral and parietal).

    • Attachments: To thoracic structures, including central tendon of diaphragm.

    • Phrenic Nerves: Outline right and left borders of the heart, innervate the diaphragm.

Surface Features of the Heart

  • Anterior (Sternocostal) Surface: Right atrium with auricle, Right ventricle, small portion of Left ventricle with cardiac apex, Left auricle, Ascending aorta, Pulmonary trunk, Superior Vena Cava (SVC).

  • Posterior Surface: Left atrium with four pulmonary veins, Left ventricle, portion of Right atrium with Inferior and Superior Vena Cava, Coronary sinus.

  • Inferior (Diaphragmatic) Surface: Left ventricle with cardiac apex, Right ventricle, portion of Right atrium with Inferior Vena Cava (IVC), Coronary sinus.