Heart Sac|Pericardial Sac.
The pericardium is a double layered heart sac of fibroserous membrane that envelops the heart and the roots (proximal ends) of the great vessels of the heart, namely the aorta, the pulmonary artery and the superior and inferior venae cavae veins. It is referred to as the heart sac only in non medical circles.
Picture of pericardium and heart.
Layers of Pericardium.
The pericardial sac has two layers:
The Fibrous Pericardium.
The fibrous pericardium forms the outer layer. It is made up of dense connective tissue and helps to protect the heart and prevents it from over expansion. It is attached to the surrounding tissues so as to the anchor the heart in its position.
The Serous Pericardium.
The serous pericardium which forms the inner layer, is again divided into two layers:
- The parietal pericardium on the outside and which is fused to the fibrous pericardium.
- The Visceral Pericardium forms the epicardium which is the outer layer of the heart.
Picture showing pericardium and its layers.
Click on image to enlarge.
The Pericardial Cavity.
The pericardial cavity is formed between the two layers of the pericardium, namely the fibrous layer and the serous layer of the pericardium. It contains the pericardial fluid or the pericardium fluid which acts as lubricant and avoids friction between these two layers of the pericardium during heart movements.
Fluid Around Heart|Pericardial Fluid.
The two layers of the pericardium form the pericardial sac or pericardial cavity which contains about 10 to 15 cc of serous fluid called the pericardial fluid. The pericardial fluid around the heart is secreted by the serous pericardium into the pericardial cavity. This fluid in the pericardium helps to give mobility to the heart in order to contract and expand by lubricating the epicardium of the heart so that the pericardial membranes slide over each other.
Functions of the Pericardium.
The pericardium serves the following functions:
- It serves as a protective coat of the heart.
- It facilitates movements of the heart by lubrication with the help of the pericardial fluid inside the two membranes of the pericardium.
- The pericardium also helps to prevent over expansion of the heart once the pericardial reserve volume is used up and the pericardium is stretched.
- As its outer layer is attached to the surrounding tissues, the pericardium helps to anchor the heart in its position.
Arterial Supply of the Pericardium.
The blood supply of the pericardium comes from the pericardiacophrenic and musculophrenic arteries which are branches of the internal thoracic arteries. It also receives blood supply from the pericardial branches of the bronchial, esophageal and the superior phrenic arteries. The innermost layer of the pericardium, the visceral layer which forms the epicardium is supplied by the coronary arteries.
Venous Drainage of the Pericardium.
The pericardium is drained by the tributaries of azygos system of veins and pericardiacophrenic veins which are tributaries of the internal thoracic veins.
Nerve Supply of Pericardium.
Its nerve supply comes from the phrenic nerves which contain the sensory and motor nerve fibers. It also gets its nerve supply from the vagus nerve and the sympathetic trunks.
The pain felt due to pericardial pathology may radiate, but is mostly felt behind the sternum (breastbone).
Common Pericardial Diseases.
- Pericardial effusion is a condition in which there is excessive formation of pericardial fluid inside the pericardium
- Pericarditis is a condition in which the pericardium becomes swollen and inflamed.
These conditions can be caused by various diseases such as infection (viral or bacterial), cancer and conditions of the heart such as a heart attack.
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