The cardiac skeleton, sometimes called the fibrous skeleton of the heart, is the structure of dense connective tissue in the heart that separates the atria from the ventricles. The cardiac skeleton establishes an electrically impermeable boundary to autonomic influence within the heart.
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The cardiac skeleton consists of four dense bands of tough elastic tissue that encircle the bases of the pulmonary trunk, aorta, and heart valves.[1] While not a "true" skeleton, it does provide structure and support for the heart, as well as isolating the atria from the ventricles. This allows the AV node and AV bundle to delay the wave of depolarisation such that the atria can contract and assist in ventricular filling before the ventricles themselves depolarise and contract (the AV bundle is the only part of the conduction system that passes from the atria to the ventricles in a normal heart). It also allows the valves (bicuspid, tricuspid, semilunar) to keep open by giving them structural support.[2]
| Fibrous rings of heart | |
|---|---|
| Transverse section of the heart showing the fibrous rings surrounding the valves | |
| Latin | anulus fibrosus dexter cordis, anulus fibrosus sinister cordis |
| Gray's | subject #138 536 |
| Fibrous trigone | |
|---|---|
| Latin | trigonum fibrosum dextrum cordis, trigonum fibrosum sinistrum cordis, trigona fibrosa |
| Gray's | subject #138 536 |
The right and left fibrous rings of heart (anulus fibrosus cordis) surround the atrioventricular and arterial orifices, and are decidedly stronger upon the left than on the right side of the heart. Physiologically, this is readily appreciated in light of the pressure differential between the right and left circuits. The right fibrous ring is known as the anulus fibrosus dexter cordis, and the left is known as the anulus fibrosus sinister cordis.[2]
The upper chambers (atria) and lower (ventricles) are divided by the unique properties of Collagen. The valve rings, central body and skeleton of the heart consisting of collagen are impermeable to electrical propagation. The only channel allowed (barring acccessory/rare preexcitation channels) through this collagen barrier is represented by a sinus that opens up to the Atrioventricular node and exits to the Bundle of His. The muscle origins/insertions of many of the cardiomyocytes are anchored to opposite sides of the valve rings.[2]
The atrioventricular rings serve for the attachment of the muscular fibers of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves.[2]
The left atrioventricular ring is closely connected, by its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the Fibrous trigone, which represents the os cordis seen in the heart of some of the larger animals, as the ox and elephant.[2]
Lastly, there is the tendinous band, already referred to, the posterior surface of the conus arteriosus.[2]
The fibrous rings surrounding the arterial orifices serve for the attachment of the great vessels and semilunar valves, they are known as The aortic annulus.[2]
Each ring receives, by its ventricular margin, the attachment of some of the muscular fibers of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed.[2]
The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium internally.[2]
From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves.[2]
The middle coat of the artery in this situation is thin, and the vessel is dilated to form the sinuses of the aorta and pulmonary artery.[2]
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This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
