pericardium

The pericardium is a double-walled sac that surrounds the heart and roots of the great vessels. It consists of an outer fibrous pericardium and an inner serous pericardium. The serous layer forms a parietal layer lining the fibrous sac and a visceral layer, or epicardium, covering the heart. The space between the parietal and visceral layers is the pericardial cavity, which normally contains a small amount of lubricating fluid.

The fibrous pericardium is a dense, inelastic membrane that stabilizes the heart within the mediastinum. It attaches anteriorly to the sternum by sternopericardial ligaments and posteriorly blends with the central tendon of the diaphragm. It is reinforced by pericardiacophrenic vessels and adjacent connective tissues. The serous pericardium forms the parietal layer that lines the fibrous sac and the visceral layer that adheres tightly to the myocardium.

The pericardial cavity houses a small volume of serous fluid, which reduces friction during cardiac movements. The cavity contains transverse and oblique sinuses, which are potential spaces used in surgical approaches to the great vessels and heart.

Nerve and blood supply: Arterial supply to the pericardium comes from branches such as the pericardiacophrenic arteries (from the internal thoracic arteries) and other small arteries from the coronary and bronchial circulations; venous drainage mirrors these sources, draining to the azygos system and internal thoracic veins. Sensory innervation is mainly via the phrenic nerves (C3–C5) to the parietal and fibrous layers; the visceral pericardium has little pain innervation.

Functions include anchoring the heart to the mediastinum and diaphragm, reducing friction during movement, and limiting excessive dilation of the heart. Pericardial effusion and cardiac tamponade are clinical conditions related to fluid accumulation in the pericardial cavity.