7.7. Introducing the Pericardium
Structure of the Pericardium
The pericardium is a sac that surrounds the heart as it sits in the (inferior) middle mediastinum. It has two layers (although one of these is subdivided into another two layers, so arguably there are three layers).
The outer pericardial layer is called the fibrous pericardium. The inner two layers are both classified as serous pericardium; they are known specifically as the parietal pericardium and visceral pericardium. The visceral pericardium is intimately adhered to the cardiac muscle (myocardium), while the parietal pericardium is adhered to the fibrous pericardium. The parietal and visceral pericardial layers are actually continuous with each, at the point where the great vessels (aorta, pulmonary trunk, IVC, SVC, pulmonary veins) are connected to the heart muscle. The pericardial cavity is filled with pericardial fluid (up to 50mL). As you can see, the organisation of the pericardium closely resembles the pleura.
Functions of the Pericardium
There are two functions of the pericardium: the serous pericardium and the pericardial fluid facilitate the smooth contraction and relaxation of the heart’s chambers. The fibrous pericardium has a seemingly opposite function, but is vitally important: it restricts movement of the heart as one unit within the thoracic cavity. This restriction is aided by the presence of three ligaments that stretch between the fibrous pericardium and surrounding structures. Note that the visceral pericardium is sometimes called the epicardium because it is so tightly adhered to the cardiac muscle.