What layers compose the pericardium?

The pericardium is a double-walled sac that surrounds the heart, and it is composed of two main layers: the parietal layer and the visceral layer. The parietal layer forms the outer wall of the sac, providing structure and protection, while the visceral layer, also known as the epicardium, adheres directly to the surface of the heart itself. Together, these layers create a potential space between them, known as the pericardial cavity, which contains a small amount of pericardial fluid that serves to reduce friction as the heart beats.

The other choices refer to layers or components related to the heart but do not accurately describe the pericardium. The epicardium and myocardium, for example, are indeed components associated with the heart; however, they do not represent the pericardial layers. The endocardium is the innermost layer of the heart itself and is not involved in the structure of the pericardium. Thus, the correct identification of the layers that compose the pericardium is essential to understanding its protective role around the heart.