Download CRRM1.9 - The Heart in Situ

CRRM1.9: THE HEART IN SITU
06/11/07
LEARNING OUTCOMES
Describe the major subdivisions of the thoracic cavity and the structure of the pericardial sac and its sinuses
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The thoracic cavity is divided into three main areas: the left and right pleural cavities, containing the
lungs, and the central mediastinum
The mediastinum is a thick, flexible soft tissue partition containing the heart, oesophagus, trachea,
major nerves and systemic blood vessels
The mediastinum has superior (above T5) and inferior divisions, the latter of which has three further
subdivisions:
o Anterior – immediately posterior to the sternum and anterior to the pericardial sac
o Middle – the pericardium and heart
o Posterior – between the pericardium and thoracic vertebrae
Describe the anatomy of the superior mediastinum and the relationship between the vessels of the superior
mediastinum and the thoracic inlet
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The superior mediastinum runs from T4 up to the superior border of T1 and is continuous with the
neck
Describe the courses of the phrenic nerves and the vagi in the superior mediastinum
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The phrenic nerves arise at C3, C4 and C5 and descend through the superior mediastinum lateral to
the other related structures
The phrenic nerves continue anterior to the roots of the lungs, innervating the diaphragm
The vagus nerves (arising in the brain from the tenth cranial nerve) descend posterior and medial to
the phrenic nerves and roots of the lungs
The vagus nerves supply the oesophagus, heart and lungs
Describe the relationship of the heart to the pericardial sac
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The pericardium lies in the middle mediastinum centrally in the thoracic cavity and contains the heart
It is composed of two components:
o Fibrous pericardium – outermost layer, made of tough connective tissue
o Serous pericardium – has parietal and visceral layers, the latter of which adheres to the heart
The fibrous pericardium fuses superiorly with the great vessels and inferiorly with the central tendon
of the diaphragm
The two layers of the serous pericardium contain a narrow fluid-filled space called the pericardial
cavity which accommodates for the movement of the heart
The serous pericardium reflects around the great vessels at two key locations:
o Superiorly around the arteries, aorta and pulmonary trunk
o Posteriorly around the veins, superior and inferior vena cava and pulmonary veins
These reflections create blind-ending spaces – sinuses:
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Between the two reflections is a narrow passage with the pulmonary artery and vein on
either side which is called the transverse pericardial sinus
o Posterior to the left atrium limited by the vena cava is the oblique pericardial sinus
Pericarditis is an inflammatory condition in which the heart adheres to the pericardium, producing
chest pains (different from those associated with myocardial infarction in that they can be relieved by
sitting forward) and a discernable noise as the heart ‘rubs’ against the pericardial sac
Cardiac tamponade is where fluid or blood accumulates in the pericardial cavity (pericardial effusion)
compressing the heart, which can cause heart failure; relieved by draining fluid using a needle
In the thoracic cavity, the heart is oriented forward, downward and to the left
Explain the concept of the fibrous skeleton of the heart