Histology and Ultrastructure of the Pericardium:

H . Histologic section showing that the parietal pericardium consists of an outer fibrous layer and an inner, single layer of mesothelial cells. There are sparse small arteries and veins throughout the pericardial sac. (H&E, 25 X) I. The visceral pericardium or epicardium invests the heart and consists of a lining layer of mesothelial cells and a thin, subjacent layer of fibrous tissue that overlies the entire external surface of the heart. The epicardium is in direct contact with the subjacent myocardium, except in those areas where adipose tissue and coronary vessels are found. Other structures present include ganglion cells and nerves. The epicardium also covers the epicardial vessels which include coronary arteries, veins and lymphatics. (H&E, 40 X) J. Scanning electron micrograph of pericardial mesothelial cells with numerous long microvilli. These greatly expand the surface area of the pericardium and also functions as friction-bearing devices. {10} (4,000 X) K. Scanning electron micrograph showing a higher magnification view of the ­microvilli illustrated in J (20,000 X). L. Transmission electron micrograph of a pericardial mesothelial cell showing intercellular junctions and microvilli (10,000 X).