perikard

Perikard, or pericardium, is the double-walled sac that encloses the heart and the origins of the great vessels. It consists of a tough external fibrous pericardium and a serous pericardium. The serous layer lines the inner surface of the fibrous sac (parietal serous pericardium) and folds back to cover the heart (visceral serous pericardium, also known as the epicardium). The space between the parietal and visceral layers is the pericardial cavity, containing a small amount of lubricating pericardial fluid.

Anatomy and attachments: The fibrous pericardium attaches to the central tendon of the diaphragm and to the sternum via sternopericardial ligaments; it blends with the adventitia of the great vessels at the bases of the aorta and pulmonary trunk. The parietal serous pericardium adheres to the fibrous layer, while the visceral serous pericardium covers the heart itself. The pericardial reflections form pericardial sinuses, such as the transverse and oblique sinuses, around the roots of the great vessels.

Functions: The perikard serves to protect the heart, limit its motion within the mediastinum, and prevent overexpansion during diastole. The serous fluid reduces friction between the moving heart and surrounding structures during cardiac cycles.

Nerve and blood supply: The fibrous and parietal layers receive sensory innervation primarily from the phrenic nerves, explaining referred pain to the shoulder in some cases. Blood supply comes from pericardiacophrenic arteries (branches of the internal thoracic arteries) and other surrounding vessels; venous drainage mirrors these vessels.

Development: The perikard derives from mesodermal sources during embryogenesis, with the serous layers forming from the splitting of the coelomic mesoderm to create the pericardial cavity.

Clinical significance: Pericardial disease includes pericarditis (inflammation), pericardial effusion (fluid accumulation), cardiac tamponade (compression of the heart), and constrictive pericarditis (fibrous thickening that impairs filling).