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Fibrous skeleton of the heart
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The fibrous skeleton of the heart, also called the cardiac skeleton, consists of four fibrous rings (anuli fibrosi, singular: annulus fibrosis) and the membranous portions of the septa of the heart. This skeleton is located at the base of the ventricles, between the atria and the ventricles.
The rings of the fibrous skeleton are composed of dense, fibrous connective tissue that encircle the orifices of the heart valves. These fibrous rings are interconnected by connective tissue called the right and left trigones and form the structural support for the heart on which the valvular leaflets and cardiac muscle fibers are anchored.
This article will discuss the anatomy and function of the fibrous skeleton of the heart.
| Definition | A rigid framework of dense regular connective tissue located between the atria and the ventricles |
| Components | Four fibrous rings Right and left fibrous trigones Membranous aspects of the interatrial, interventricular and atrioventricular septa. |
| Functions | Separates of the atria from the ventricles Maintains valve orifices open Provides attachment points for valve leaflets and cusps Acts as an electrical insulator between the atria and ventricles Framework for the attachment of myocardial fibers |
Anatomy
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The fibrous skeleton of the heart is a rigid framework of dense regular connective tissue located in a plane between the atria and the ventricles. This complex structure consist of three main components. These are the four fibrous rings, right and left fibrous trigones, and finally the membranous aspects of the interatrial, interventricular and atrioventricular septa.
The four fibrous rings surround the orifices of the pulmonary, aortic and atrioventricular valves, giving attachments to their leaflets and resisting excessive distention. The left fibrous ring encircles the left atrioventricular valve (mitral valve) and the right fibrous ring surrounds the right atrioventricular valve (tricuspid valve). The pulmonary ring corresponds to the pulmonary valve as does the aortic ring to the aortic valve.
The right and left trigones are interconnections between the fibrous rings, and the strongest parts of the skeleton. A thickened connective tissue connection between the aortic ring and right atrioventricular ring forms the right trigone, while the left trigone is formed by a similar connective tissue bridge between the aortic ring and the left atrioventricular ring.
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Functions
The fibrous skeleton of the heart performs several important functions and thus plays a vital role in supporting both the structure and function of the heart.
- It helps keep the orifices of the valves it surrounds patent, and also serves as points of attachment for the leaflets and cusps of these valves.
- The fibrous skeleton separates the atrial musculature from that of the ventricles. It serves as the framework for the attachment of myocardial fibers, with atrial fibers arising from the upper border of the rings and ventricular fibers originating from the lower border of the rings.
- The fibrous skeleton serves as an electrical insulator, partitioning electrical impulses conducted through the musculature of the atria and ventricles, allowing them to contract independently. In line with this, the fibrous skeleton provides passage for the atrioventricular bundle, which serves as the only electrical connection between the atria and ventricles.
Looking for a want a fun way to learn the structure of the heart? Check out our diagrams, quizzes and worksheets of the heart.
Clinical relations
Calcification of the fibrous skeleton of the heart
Calcification of the fibrous skeleton of the heart is a common finding in elderly people and is a recognized marker of severe atherosclerosis. Calcifications may occur in various areas of the fibrous skeleton but are more commonly observed in the mitral and aortic annuli. Extensive calcification of the fibrous skeleton may result in atrioventricular (AV) conduction disorders but may also increase the risk of injury and complications during or following surgical and transcatheter interventions.
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