Q. What do you mean by Pericardium?

Pericardium is the sac covering the heart. Pericardium consists of two layers-the visceral pericardium (epicardium) and the parietal pericardium. The visceral pericardium directly lines the heart surface. The cavity between the two layers of the pericardium contains approximately 15 to 35 ml. of serous fluid-the pericardial fluid. The visceral pericardium is a thin membrane-a monolayer of mesothelial cells, while the parietal pericardial thickness may be up to 2.5 to 3.0 mm. Perietal pericardium is attached loosely by ligaments to sternum and vertebral bodies and firmly to central tendon of the diaphragm.

The phrenic nerves lie over the parietal pericardium and supply most of it. Vagal fibres from oesophageal plexus also supply pericardium. The internal mammary arteries and small branches from aorta supply the pericardium. The parietal pericardial lymphatics drain to the anterior and posterior mediastinal nodes while the visceral pericardial lymphatics drain to tracheal and bronchial mediastinal nodes. The pericardium buttress the thinner chambers of the heart, the atria and right ventricle and maintains the normal diastolic pressures and dimensions in these chambers. The pericardium can prevent acute cavitary dilatation. The pericardial fluid reduces the friction during heart movement. The ligamentous attachment of pericardium to the neighbouring structures prevent cardiac displacement. The normal intrapericardial pressure can vary from -5 to +5 mm. of Hg. though mostly it is negative. The pericardial pressure varies during respiration along with pleural pressure.