Which membrane surrounds the heart?

The membrane that surrounds the heart is the pericardium. This structure is a double-walled sac that encompasses the heart, providing both protective and structural support. The outer layer, known as the fibrous pericardium, is dense and helps anchor the heart within the thoracic cavity, preventing excessive movement. The inner layer, called the serous pericardium, is further divided into the parietal and visceral layers, with the visceral layer being in direct contact with the heart muscle. This arrangement helps reduce friction as the heart beats, ensuring smooth movement.

Understanding the role of the pericardium is crucial for recognizing its importance in protecting the heart from infection and trauma, and in maintaining the position of the heart within the chest. The other choices refer to different anatomical structures: the mediastinum is the central compartment of the thoracic cavity that includes the heart among other things; the pleura are membranes surrounding the lungs; while the endocardium is the inner lining of the heart chambers themselves. Each of these structures has distinct functions but does not surround the heart in the same protective manner as the pericardium.