Pericardium: structure and function in health and disease.

Normal pericardium consists of an outer sac called fibrous pericardium and an inner one called serous pericardium. The two layers of serous pericardium: visceral and parietal are separated by the pericardial cavity, which contains 20 to 60 mL of the plasma ultrafiltrate. The pericardium acts as mechanical protection for the heart and big vessels, and a lubrication to reduce friction between the heart and the surrounding structures. A very important role in all aspects of pericardial functions is played by mesothelial cells. The mesothelial cells form a monolayer lining the serosal cavity and play an important role in antigen presentation, inflammation and tissue repair, coagulation and fibrinolysis. The two major types of mesothelial cells, flat or cuboid, differ substantially in their ultrastructure and, probably, functions. The latter display abundant microvilli, RER, Golgi dense bodies, membrane-bound vesicles and intracellular vacuoles containing electron-dense material described as dense bodies. The normal structure and functions of the pericardium determine correct healing after its injury as a result of surgery or microbial infection. The unfavorable resolution of acute or chronic pericarditis leads to the formation of adhesions between pericardial leaflets which may lead to serious complications.