The loose-fitting sac around the heart is the:
A.
Fibrous pericardium.
B.
Epicardium.
C.
Endocardium.
D.
Visceral pericardium.
The answer and exlanation is:
The correct answer is A. Fibrous pericardium.
Explanation:
The heart is enclosed within a protective sac known as the pericardium, which consists of two primary layers: the fibrous pericardium and the serous pericardium.
- Fibrous Pericardium:
- This is the tough, dense, and inelastic outer layer of the pericardium. It is made of fibrous connective tissue and functions as a protective layer. The fibrous pericardium prevents the heart from over-expanding when blood volume increases, and it anchors the heart in the chest cavity, attaching to surrounding structures like the diaphragm, the sternum, and the great vessels (e.g., aorta, vena cava).
- Since it is loose-fitting, it allows the heart to move slightly within the chest cavity during contractions and expansions but restricts excessive movement that could damage the heart or surrounding tissues.
- Serous Pericardium:
- This is a double-layered structure located beneath the fibrous pericardium. It consists of the parietal layer (which lines the internal surface of the fibrous pericardium) and the visceral layer (also called the epicardium when referring to the heart surface). The space between these two layers, known as the pericardial cavity, contains a small amount of fluid that reduces friction during heartbeats.
- Epicardium:
- Also known as the visceral layer of the serous pericardium, the epicardium directly covers the heart muscle and forms the outer layer of the heart wall. It is not a loose-fitting sac.
- Endocardium:
- This is the innermost layer of the heart wall that lines the heart chambers and covers the heart valves. It is not involved in forming the sac around the heart.
- Visceral Pericardium:
- This is another term for the epicardium, the inner layer of the serous pericardium that adheres closely to the heart.
The fibrous pericardium is the correct choice because it is the loose-fitting, fibrous sac that surrounds and protects the heart.