THE THORAX
• • • • •
Trachea; Oesophagus; Thoracic duct; Lymph nodes; and Nerves. The anterior mediastinum contains the:
• Thymus; • Mammary vessels; and • Lymph nodes. The posterior mediastinum contains the: • • • •
Descending aorta; Oesophagus; Azygos venous system; Thoracic duct; and
• Para-aortic, oesophageal and paraspinal nodes. The middle mediastinum contains the: • • • •
Heart and pericardium: Nerves; Lymph nodes; and Great vessels.
forms the base or posterior part, with the superior and inferior pulmonary veins draining into its four corners. The right atrium forms the right border, with superior and inferior venae cavae draining into its upper and lower parts. The apex and left border are formed by the left ventricle. The right ventricle forms the anterior part. The inferior (diaphragmatic) part of the heart is formed by both ventricles anteriorly and a small part of right atrium posteriorly where the IVC enters this chamber. The oblique orientation of the heart causes the ventricles to lie anterior and inferior to the atria. The heart is also rotated in a clockwise fashion about its axis, so that the right atrium and ventricle are at a slightly higher level than their left counterparts. The interatrial and interventricular septa are said to lie in the left anterior oblique plane. This means that the long axis of the septa runs anteriorly to the left. The tricuspid and mitral valves, which separate the right and left atria and ventricles respectively, are roughly vertically oriented. The plane of the valves is also inclined inferiorly and to the left. This means that the transverse axis of the pair of valves runs to the right and anteriorly, and they are said to lie in the right anterior oblique plane. Pericardium (Fig. 4. 23)
THE HEART Gross anatomy and orientation (Figs 4. 20-4. 22; also Figs 4. 6 and 4. 7) The heart is pyramidal in shape and lies obliquely in the chest. Its square-shaped base points posteriorly and the elongated apex to the left and inferiorly. The left atrium
This is a closed sac consisting of parietal and visceral layers that enclose a potential space which contains 20-25 mL of serous fluid. It is draped over the heart and great vessels. The visceral layer adheres to the myocardium and is also known as the epicardium. The parietal layer is free, except inferiorly, where it is bound to the central tendon of the diaphragm, and superiorly where it fuses with the covering of the great vessels. The pericardial reflections, which are really the boundaries of the closed sac, are found posteriorly
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