9.7 Central Fibrous Body

Central Fibrous Body is a dense, fibrous connective tissue structure located in the heart, forming a crucial component of the fibrous skeleton. It serves as the central anchoring point for the heart valves and provides mechanical support and electrical insulation between the atria and ventricles. This structure integrates with adjacent fibrous rings of the atrioventricular valves and the membranous septum, ensuring the integrity and coordination of cardiac function.

Position and General Anatomy

The Central Fibrous Body is situated at the center of the heart's fibrous skeleton, lying between the atria and ventricles. It occupies the area where the atrioventricular septum is located, specifically at the junction of the right atrium, right ventricle, and the membranous parts of the interventricular septum. It is closely associated with the base of the aortic root and lies medial to the tricuspid and mitral valve annuli.

This body forms the core of the heart’s fibrous skeleton, acting as a pivotal connective hub that connects the fibrous rings of the atrioventricular valves and the aortic valve. Its anatomical relationships include proximity to the membranous septum and the central part of the interventricular septum, contributing to the structural partition of the heart chambers.

Composition and Structural Features

The Central Fibrous Body is composed primarily of dense collagenous connective tissue, providing rigidity and tensile strength. This collagen-rich tissue lacks contractile elements, distinguishing it from the adjacent myocardium. It also contains embedded fibroblasts and sparse elastic fibers that contribute to its resilience and limited elasticity.

This dense connective tissue mass forms a continuous fibrous framework that supports the valvular leaflets by anchoring their cusps and chordae tendineae. The rigidity of the Central Fibrous Body prevents excessive dilation of the valve orifices during the cardiac cycle, maintaining valvular competence.

Continuity with Adjacent Structures

Right Trigone and Central Fibrous Body Continuity

The right fibrous trigone is a thickened band of fibrous tissue that connects the right atrioventricular ring (tricuspid valve annulus) with the aortic and central fibrous body. It acts as a bridge transmitting mechanical forces and electrical impulses between these structures. The Central Fibrous Body forms the medial portion of this trigone, integrating the fibrous rings and contributing to the stability of the right atrioventricular junction.

Atrioventricular (AV) Septal Interface

At the atrioventricular septum, the Central Fibrous Body forms a firm union with the membranous septum. This interface provides electrical insulation, preventing direct conduction of impulses from atrial myocardium to ventricular myocardium, except through the specialized conduction system. The central fibrous tissue here separates the atria from the ventricles structurally and functionally.

Aortic Root Interface

The base of the aortic valve, known as the aortic root, is partially supported by the Central Fibrous Body. The fibrous ring of the aortic valve merges with the central fibrous mass, creating a continuous supportive frame that maintains the position and shape of the aortic valve annulus. This continuity is essential for the proper coaptation of the aortic valve cusps during systole and diastole.

Tricuspid and Mitral Valve Interfaces

The Central Fibrous Body connects to the fibrous rings of both the tricuspid and mitral valves. On the right side, the tricuspid fibrous ring attaches to the body’s lateral aspects, while medially, the mitral fibrous ring integrates with the left side of the central fibrous mass. These attachments ensure coordinated function and mechanical stability of the atrioventricular valves during cardiac contraction and relaxation.

Membranous Septum and Central Fibrous Body Union

A key anatomical feature is the union between the membranous interventricular septum and the Central Fibrous Body. The membranous septum is a thin, fibrous partition that completes the interventricular septum inferiorly and posteriorly. It inserts into the Central Fibrous Body, anchoring the thin septal tissue to the rigid fibrous skeleton. This union plays a crucial role in maintaining septal integrity and is also a landmark for the conduction system's atrioventricular node and bundle of His.

Myocardial Attachments

While primarily fibrous, the Central Fibrous Body also serves as an attachment site for myocardial fibers. Myocardial muscle bundles from the atria and ventricles insert onto the periphery of the body, anchoring the contractile tissue to the fibrous skeleton. This arrangement allows for efficient transmission of contractile forces while preserving the electrical insulation properties of the fibrous core.

Spatial Mapping of the Central Fibrous Body

The Central Fibrous Body occupies a central location within the heart’s basal fibrous skeleton, forming a roughly quadrangular mass bounded by the following anatomical landmarks:

• Superiorly: the aortic valve annulus and aortic root
• Inferiorly: the membranous septum and interventricular septum
• Laterally: the tricuspid valve annulus on the right and mitral valve annulus on the left
• Anteriorly and posteriorly: adjacent myocardial tissue and fibrous cardiac structures

This spatial arrangement highlights the Central Fibrous Body as a pivotal connective and structural element uniting the cardiac fibrous skeleton, valves, septa, and myocardium.