Morphology/Structure
The structure of the heart and muscular fibers are set around a fibrous cardiac skeleton consisting of dense connective tissue. The bulk of the fibrous skeleton consists of four fibrous rings that surround the orifices of the valves. These are:
- the right fibrous ring, which sits around the right atrioventricular valve;
- the left fibrous ring, which sits around the left atrioventricular valve;
- the aortic fibrous ring, which sits around the aortic valve;
- the pulmonary fibrous ring, which sits around the pulmonary valve.
Key Features/Anatomical Relations
The right fibrous ring is connected to the aortic ring by a roughly triangular mass of fibrous tissue called the right fibrous trigone. Likewise, the left fibrous ring is connected to the aortic ring by the left fibrous trigone. These fibrous trigones form the strongest portions of the fibrous skeleton. The rings are also connected to the membranous part of the upper interventricular septum.
Function
The collagenous properties of the fibrous rings separate the atria from the ventricles. This helps to separate the electrical activities between the chambers by insulating the propagation of electrical impulses during a heartbeat. The region where the atrioventricular bundle passes from the atrioventricular node to the ventricles does not contain collagen and permits the propagation of electrical impulses. It also provides a direct attachment for cardiac muscle and the membranous interventricular septum.
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Cardiac Skeleton
The cardiac skeleton consists of four rings of dense connective tissue that surround the AV canals (mitral and tricuspid) and extend to the origins of the aorta and the pulmonary trunk, providing structure and support for the heart as well as electrical isolation between the atria and the ventricles.
