Which structure surrounds and protects the heart as a double membrane sac?

Which structure surrounds and protects the heart as a double membrane sac?

• A. Pericardium
• B. Endocardium
• C. Myocardium
• D. Aorta

Answer: (A)

The heart is enclosed by a protective double-layered membrane called the pericardium. This sac has two layers: the outer parietal pericardium and the inner visceral pericardium (which is the epicardium when it lies directly on the heart). The narrow space between these layers, the pericardial cavity, contains a small amount of lubricating fluid that reduces friction as the heart beats. This arrangement helps anchor the heart in the mediastinum, limits its distention, and provides a barrier against infection. The other structures mentioned serve different roles: the endocardium lines the interior of the heart chambers, the myocardium is the heart muscle itself, and the aorta is the main artery leaving the heart. Therefore, the double-membrane sac surrounding and protecting the heart is the pericardium.

The heart is enclosed by a protective double-layered membrane called the pericardium. This sac has two layers: the outer parietal pericardium and the inner visceral pericardium (which is the epicardium when it lies directly on the heart). The narrow space between these layers, the pericardial cavity, contains a small amount of lubricating fluid that reduces friction as the heart beats. This arrangement helps anchor the heart in the mediastinum, limits its distention, and provides a barrier against infection. The other structures mentioned serve different roles: the endocardium lines the interior of the heart chambers, the myocardium is the heart muscle itself, and the aorta is the main artery leaving the heart. Therefore, the double-membrane sac surrounding and protecting the heart is the pericardium.