Cardiac Path Online
Normal Anatomy - Ventricle of the Heart
The Right Ventricle:
The ventricles have three components - the inlet, the apical trabecular component, and the outlet.
The inlet of the right ventricle extends from the atrio-ventricular junction, being contained and limited by the tension apparatus of the tricuspid.
The tension apparatus stops the atrio-ventricular valves from turning inside-out during ventricular contraction.
The three leaflets of the tricuspid valves - Septal ; Antero-superior ; and Inferior or mural location.
The medial papillary muscle supports the zone of apposition between septal and antero-superior leaflets. Image Link
It is these zones of apposition between adjacent leaflets which we define as the commissures of the valve.
A much larger papillary muscle, the anterior papillary muscle, supports the commissure between antero-superior and inferior leaflets, although this muscle often inserts along the edge of the extensive antero-superior leaflet.
The third commissure, between inferior and septal leaflets, is supported by the smaller inferior papillary muscle.
The most characterisitic feature of the tricuspid valve is the multiple attachment of cords from the septal leaflet to the ventricular septum.
The characterisitic feature of the apical component of the ventricle is its very coarse trabeculations.
The very prominent septomarginal trabeculation reinforces the surface of the septum and divides in the roof of the ventricle into two limbs which clasp the infolding of the heart wall forming the ventricular roof.
This infoldings is the supra-ventricular crest.
It is the part of the ventricle which wraps itself around the origin of the aorta from the left ventricle.
The posterior limb of the septomarginal trabeculation gives rise to the medial papillary muscle, while the anterior limb runs into the outlet component to support the leaflets of the pulmonary valves.
The body of the trabeculation then runs down towards the apex of the right ventricle, where it gives rise to the anterior papillary muscle, before breaking up into the general apical trabeculations.
The anterior papillary muscle itself continues as an important muscular strand, the moderator band, to the parietal wall of the right ventricle.
A further series of trabeculations run from the anterior surface of the septomarginal trabeculation onto the parietal wall of the right ventricle.
These are septoparietal trabeculations.
The major feature of the outlet of the right ventricle is that it is a complete muscular structure.
Known as the infundibulum, it can be lifted clear of the heart without entering the cavity of the left ventricle.
It supports the three leaflets of the pulmonary valve in semilunar fashion.
Each of the leaflets is attached such that the base is within the ventricle while the tip of the zone of apposition takes origin from the prominent junction between the sinuses of the pulmonary trunk and the tubular arterial trunk.
Each semilunar attachment, therefore, marking the haemodynamic ventriculo-arterial junction, crosses the circular line of attachment of the fibroelastic pulmonary trunk to the muscular right ventricular infundibulum.
This arrangement permits the valvar leaflets to open and close in competent fashion.
The zones of apposition of the leaflets, or commissures, extend from the peripheral attachment at the sinutubular junction to the centre of the valve.
This mechanism is also seen within the aortic valve.
The understanding of the arrangement is important because of the frequent use of the term "annulus" when describing the arterial valvar complex.
None corresponds to the semilunar attachment of the leaflets.
This is unlike the arrangement in the atrio-ventricular valves where the leaflets are attached at the atrio-ventricular junctions in true annular fashion.
The left ventricle has the mitral valve within its inlet component, has fine apical trabeculations with a smooth septal surface, and has the aortic valve in its outlet component.
The most characterisitic feature of the normal ventricle is the overlapping of the inlet and outlet components, with fibrous continuity between the leaflets of the mitral and aortic valves in the ventricular roof.
The mitral valve's old name was the bicuspid valve, thus distinguishing it from the atrio-ventricular valve of the right heart with its three leaflets.
The mitral valve has two leaflets and these are markedly dissimilar in their structure.
One leaflet guards one-third of the valvar circumference and is deep.
The other is much shallower and guards along its length known as "scallops".
The leaflets are often said to be "anterior" and "posterior".
When viewed with the heart in position within the body, the valvar orifice is markedly oblique and these terms are not strictly correct.
Some prefer to describe them as the mural and aortic leaflets.
A valve with two leaflets can have only one zone of apposition between them.
The mitral valve, has only one commissure.
This extends from antero-laterally to postero-medially within the atrio-ventricular junction.
Since pathologists tend to view the valve when opened, they more usually describe the two ends of the zone of apposition as paired commissures within the valve.
The tension apparatus from both sides of the ends of adjacent leaflets are attached to the paired papillary muscles, also located antero-laterally and postero-medially within the ventricular mass.
The two muscles are positioned directly beneath the ends of the commissure so as to act at the maximal mechanical efficiency.
In the normal valve, all parts of the leaflets usually have cords connecting the free edge to the papillary muscle.
Two cords, on the ventricular aspect of the aortic leaflet, are particularly prominent and are called the strut cords.
Fan-shaped cords are found at the ends of the zone of apposition between the leaflets and also between the scallops of the mural leaflet.
Other shorter cords, basal cords, run directly from the undersurface of the mural leaflet to the parietal ventricular wall.
Similar variation in cordal morphology is also seen in the tricuspid valve.
The interrelationship of aortic and mitral valves in the roof of the ventricle have an important consequence on septal anatomy.
The larger part of the interventricular septum is a muscular structure.
Because of the overlapping of the inlet by the outlet of the left ventricle, however, the outlet of the left ventricle is adjacent to the inlet of the right.
This can be readily demonstrated by removing one of the sinuses of the aortic valve.
It can then be seen that the rightward margin of the area of continuity between the two sides of the heart between the leaflets of the tricuspid valve.
The intervening area, composed of fibrous tissue is incorporated as part of the septum between the two sides of the heart.
This fibrous component is called the membranous septum.
It is itself divided by the attachment of the tricuspid valve on its right side into one part between the ventricles (interventricular membranous septum) and a second part interposed between right atrium and subaortic outflow tract (the atrioventricular membranous septum).
This part of the septum achieves added importance since it is pierced by the axis of atrioventricular conduction tissue (the penetrating atrioventricular bundle or bundle of His).
The aortic valve itself is arranged in a fashion similar to that described for pulmonary valve.
Its three leaflets have semilunar attachments which cross the anatomic ventriculo-arterial junction. Image Link
Unlike the pulmonary valve, these leaflets are not exclusively supported by ventricular musculature.
Two of the leaflets do have such muscular support ,these being the ones adjacent to, or facing, the leaflets of the pulmonary valve. These facing leaflets guard the aortic sinuses which give rise to the coronary arteries and hence are called the right coronary and left coronary leaflets.
The third leaflet, guarding the sinus which does not give rise to a coronary artery, is the non-coronary leaflet.
It is parts of the non-coronary and left coronary leaflets which are in fibrous continuity with the aortic leaflet of the mitral valve, this important area is also known as the aorto-mitral curtain.
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