Cardiac skeleton
Encyclopedia
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.
, 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.
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.
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.
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 valve
s.
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
.
Lastly, there is the tendinous band, already referred to, the posterior surface of the conus arteriosus
.
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.
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.
The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium
internally.
From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves.
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.
Dense connective tissue
Dense connective tissue, also called dense fibrous tissue, has fibers as its main matrix element. Dense connective tissue is mainly composed of collagen type I. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that manufacture the fibers. Dense connective tissue...
in the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
that separates the atria from the ventricles
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
. The cardiac skeleton establishes an electrically impermeable boundary to autonomic influence within the heart.
General form and anatomy
The cardiac skeleton consists of four dense bands of tough elastic tissue that encircle the bases of the pulmonary trunk, aorta, and heart valves. While not a "true" skeletonSkeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
, 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.
Fibrous rings
The right and left fibrous rings of heart (anulus fibrosus cordis) surround the atrioventricularAtrioventricular
Atrioventricular can refer to:*Left atrioventricular opening*Atrioventricular fistula*Atrioventricular node*The term "Atrioventricular valves" is used to describe the mitral valve and tricuspid valve....
and arterial orifices, and are decidedly stronger upon the left than on the right side of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. 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.
The upper chambers (atria) and lower (ventricles
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
) are divided by the unique properties of Collagen
Collagen
Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of mammals. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content...
. 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
Atrioventricular node
The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...
and exits to the Bundle of His
Bundle of His
The bundle of His, known as the AV bundle or atrioventricular bundle, is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node to the point of the apex of the fascicular branches...
. The muscle origins/insertions of many of the cardiomyocytes are anchored to opposite sides of the valve rings.
The atrioventricular rings serve for the attachment of the muscular fibers of the atria
Atria
Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...
and ventricles
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
, and for the attachment of the bicuspid and tricuspid valve
Tricuspid valve
The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. They are connected to the papillary muscles by the chordae...
s.
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
Ox
An ox , also known as a bullock in Australia, New Zealand and India, is a bovine trained as a draft animal. Oxen are commonly castrated adult male cattle; castration makes the animals more tractable...
and elephant
Elephant
Elephants are large land mammals in two extant genera of the family Elephantidae: Elephas and Loxodonta, with the third genus Mammuthus extinct...
.
Lastly, there is the tendinous band, already referred to, the posterior surface of the conus arteriosus
Conus arteriosus
The conus arteriosus is a conical pouch formed from the upper and left angle of the right ventricle in the chordate heart, from which the pulmonary trunk arises....
.
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.
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
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
is firmly fixed.
The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium
Endocardium
The endocardium is the innermost layer of tissue that lines the chambers of the heart. Its cells are embryologically and biologically similar to the endothelial cells that line blood vessels....
internally.
From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves.
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.
See also
- chordae tendineaeChordae tendineaeThe chordae tendineae, or heart strings, are cord-like tendons that connect the papillary muscles to the tricuspid valve and the mitral valve in the heart....
- Fibrous ring of intervertebral diskAnnulus fibrosus disci intervertebralisEach intervertebral fibrocartilage is composed, at its circumference, of laminæ of fibrous tissue and fibrocartilage, forming the annulus fibrosus.-Spelling notes:...
External links
- Description at cwc.net
- Diagram of skeleton at vanderbilt.edu
- Another illustration at vanderbilt.edu
- Overview at vanderbilt.edu, – "left fibrous trigone", – "right fibrous trigone"
- Histology (see slide #96)
