The term pericardium is derived from the Greek prefix peri- (“around”) and kardia (“heart”), implying a structure that envelops or encloses the heart. Morphologically, the pericardium is a fluid-filled sac-like structure that surrounds the heart.
Anatomic Structure
The pericardium is a double-walled structure, made up of an outer fibrous layer and an inner serous layer. The fibrous layer is a single, connective tissue layer, made up of collagen (type I and type III mainly) and elastin fibers; it is elastic and yet non-distensible. This layer of the pericardium is held in position cranially by its membranous folds interdigitating with the tunica adventitia of the great vessels; caudally by ligaments connecting to the central tendon of the diaphragm;
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The parietal layer lines the inner regions of the fibrous pericardium, while the visceral layer lines the outer layer of the heart and therefore it is called epicardium.
Pericardial Cavity
A void space found among the two linings of serous pericardium is called pericardial cavity, which encircles the heart. Between the parietal and visceral layer is the pleural cavity, which holds the pleural fluid. About 20–30 ml in volume, this serous fluid acts as a lubricant and minimizes friction between the epicardium and parietal layer as the heart muscles expand and contract with the beating of the heart. Thus, the pericardial cavity allows the heart movement to be flexible.
The pericardial cavity surrounds the heart totally except at the inlet and outlet of the cardiac vessels, where they form two significant tubes. One of the tubes serves as an interconnection to the inferior and superior vena cava and the pulmonary veins, whereas the other connects the aorta and the pulmonary trunk.
Blood Supply and Innervation of the
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There are two such sinuses in the pericardial cavity: the transverse pericardial sinus and the oblique pericardial sinus. Both these are formed during embryonic folding of the heart tube during ontogeny.
The reflections (folds) of the serosal layer result in the formation of a set of complex tubes, one enclosing the aorta and the pulmonary trunk and the other enclosing the superior and inferior vena cave and the pulmonary veins. This results in a transverse sinus across the pericardium that separates the arterial blood vessels and the venous blood vessels. The index finger can pass though the transverse sinus, which helps surgeons to identify the blood vessels of the heart during coronary artery bypass surgery.
Oblique sinus is formed by reflection of the pericardial membranes onto the pulmonary veins. It is bounded by the inferior vena cava and by the right pulmonary veins on one side and the left pulmonary veins on the other.
Functions of the Pericardium
The pericardium is known to have some specific functions:
• Tethering: pericardium holds the heart in place within the cardiac