What type of membrane surrounds the heart?

The heart is surrounded by a dual-layered membrane known as the pericardium. This structure serves to protect the heart and prevent it from overexpanding as it fills with blood. The pericardium also provides lubrication, reducing friction between the heart and surrounding tissues during the heart's rhythmic movements.

The pericardium consists of two layers: the fibrous pericardium, which is the tough outer layer that provides mechanical support, and the serous pericardium, which creates a smooth, frictionless environment for heart movement. This design is crucial for effective cardiac function, as it helps maintain the heart's position in the thoracic cavity while allowing it to expand and contract without constraint.

The other options relate to different body regions or structures. The peritoneum encloses the abdominal organs, the pleura is associated with the lungs, and the endocardium is a thin membrane that lines the heart's chambers but does not encase the heart itself. Understanding these distinctions is key to grasping the anatomical relationships surrounding the heart.