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Heart & vascular pathology

General

Valves

Author: R. Amita, M.D.

Last author update: 1 November 2015

Last staff update: 4 January 2021

Copyright: 2015-2024, PathologyOutlines.com, Inc.

PubMed Search: Cardiac valve [title]

Table of Contents

Cite this page: Amita R. Valves. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/heartvalves.html. Accessed December 26th, 2024.

Definition / general

The four heart valves (tricuspid, pulmonic, mitral, aortic) enable blood to flow in a unidirectional way
They open and close over three billion times during a normal life
Between 1 and 20 liters per minute of blood flows through the valves during rest, exercise or other conditions
Each heart valve is composed of different structures, with different histological profiles to provide optimal function for varied roles in the cardiac cycle

Diagrams / tables

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Fibrous skeleton of heart

Aortic root structures

Mitral valve annulus

Gross description

Tricuspid valve (Valve atrioventricularis dexter):

Composed of an anterior, anterosuperior, ventral or mural leaflet (Cuspid anterior); a posterior, inferior or dorsal leaflet (Cuspis posterior) and a septal or medial leaflet (Cuspis septalis)
It is positioned between the right atrium and the right ventricle and builds a structural unit with the annulus, chordae tendinae and the papillary muscles
The three leaflets of the tricuspid valve differ in size
- The mural or anterior leaflet is the largest; it stretches from the infundibular area downwards to the inferolateral wall of the right ventricle
- The septal or medial leaflet is attached to both the membranous and muscular portions of the ventricular septum
- The posterior leaflet is the smallest and attached to the tricuspid ring along its posteroinferior border
Sometimes, four leaflets can be identified - the posterior leaflet can be divided or an additional leaflet is positioned between the posterior and the septal one
The free margins of the leaflets show an arcade-like composition and terminate into the chordae tendinae
Similar to the mitral valve leaflets, closure of the tricuspid valve is achieved by a plane of attachment of the leaflets to each other, by which the subvalvular apparatus prevent the leaflets from passing into the atrium
The tricuspid leaflets differ from the mitral leaflets in being thinner, more translucent, and less easily separated into well defined leaflets
The tricuspid orifice is larger than the mitral valve orifice

Pulmonary / pulmonic valve:

Connects the Conus arteriosus (infundibulum) of the right ventricular outflow tract and the truncus pulmonalis of the pulmonary artery
The root consist of the sinus (sinus trunci pulmonalis), the annulus, the commissures, the leaflets and the sinotubular junction
The aortic and pulmonary leaflet show similar histological characteristics
The pulmonary leaflets are thinner and the noduli of Arantii is smaller compared with the aortic leaflets
Pulmonary valve leaflets consist of the hinge, the belly, the coapting surface and the lannula with the noduli of Arantii
The belly, which forms the main area of one leaflet, is almost transparent in its center
In the zone of the hinge area, the leaflets are attached to the pulmonary annulus

Mitral valve (Valva atrioventricularis sinistra OR valva bicuspidalis OR valva mitralis)

The mitral valve is composed of the annulus, 2 leaflets, the chordae tendinae and the papillary muscles
The annulus is the opening area of the mitral valve, composed anteriorly of a fibrous component which is localized between the two fibrous trigones, the trigonum fibrosum dextrum (the central part of the skeleton of the heart) and the trigonum fibrosum sinistrum
The anterior leaflet is the larger of the two leaflets, and is divided into the zone of attachment to the annulus, the 'translucent' zone and the 'rough' zone, where the chordae tendinae are attached to the ventricular side of the leaflet and into the free margin
The posterior leaflet is divided into three parts: posteromedial or right, intermediate and anterolateral or left
Although the posterior leaflet is attached to almost two thirds of the circumference, and its area is significantly larger than the area of the anterior leaflets, it participates to a lesser extent in closure of the mitral orifice
Both leaflets meet each other at the two commissures (posteromedial and anterolateral)
On the leaflets, the majority of the chordae insert either at the free margin or behind the free margin at the ventricular side (rough zone)

Aortic valve (Valva Aortae)

The aortic root is composed of the annulus, commissures, interleaflet triangles (trigones), sinuses of Valsalva, sinotubular junction and 3 leaflets (Ann Cardiothorac Surg 2013;2:53)
Supports the aortic valve and forms the anatomic boundary between the left ventricle and the aorta
Commissure:
- Apex of the crown-like annulus where the two leaflets are attached to the aortic wall at the height of the sinotubular junction
- The commissure between the right and left coronary leaflets is positioned anteriorly and is more or less opposite to the corresponding commissure of the pulmonary valve
- The commissures have a fibrous structure and suspend the valve leaflets
Leaflets:
- Originally named according to their anatomical position as anterior and posterior right and left leaflet (British Terminology Anatomical System) or anterior and right and left posterior leaflet (International Terminology Nomenclatura Anatomica)
- In the 1950s, surgeons adopted the simpler terminology of non coronary leaflet, right coronary leaflet and left coronary leaflet, based on their relationship to the coronary ostia
- The triangle between the right and non-coronary sinuses is in direct continuity with the membranous septum proximally
- The bundle of His, coming from the anterior extension of the AV node, penetrates through the central fibrous body just below the inferior margin of the membranous ventricular septum at the crest of the muscular ventricular septum under this triangle; it is closely related to the septal leaflet of the tricuspid valve
- Aortic valve leaflet consist of four components: hinge, belly, coapting surface, lannula with the noduli of Arantii

Gross images

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The four heart valves

Tricuspid valve

Isolated tricuspid valve

Pulmonary valve

Mitral valve and aortic root

Mitral leaflets

Mirtal valve apparatus

Mitral valve
commissural
chordae tendinae

Aortic value, right coronary leaflet

Microscopic (histologic) description

Tricuspid valve:

The leaflets are composed of a fiber skeleton and an endocardial surface
The atrial layer of the endocardium shows a smooth surface, and is a monolayer of endothelium
These cells are interconnected in various fashions
They show either a straight border interlocked with each other, or 'roof tile'-like overlaps
The endothelium is underlined by a basal membrane, composed of an osmiophilic lamina densa and an osmiophobic lamina rara
The lamina spongiosa is composed of loosely arranged layer of connective tissue
The lamina fibrosa is composed of dense collagenous fibers which form a solid plane

Pulmonary valve:

Light microscopy shows five layers between the ventricular and arterial endocardial layers of the leaflet: lamina ventricularis, lamina radialis, lamina spongiosa, lamina fibrosa and lamina arterialis
Lamina ventricularis: layer under the ventricular endothelium; composed of a tight network of reticular fibers with only rare thin collagenous fibers and elastic fibers; thickness is 21 to 48 mm
Lamina radialis: next layer; incorporates radial oriented collagenous and elastic fibers with some reticular fibers in between; proceeds into the endocardium and the subendocardial layer of the ventricle; thickness is 58 to 108 mm
Lamina spongiosa: composed of loosely arranged reticular fibers with bundles of collagenous and some elastic fibers; many of the collagenous fibers radiate from the lamina radialis and lamina fibrosa into this layer, which sometimes make it difficult to identify; thickness is 40 to 300 mm
Lamina fibrosa: circular arranged collagen fibers connected to the annulus; thickness is 80 to 170 mm
Lamina arterialis: layer under the endothelium at the arterial side; composed of a thin layer of reticular fibers and is not always present in light microscopic sections

Mitral valve:

Leaflets are composed of a fibrous skeleton with an endocardial surface
The atrial layer has a smooth endocardial cell layer
On the anterior leaflet, this smooth endocardial layer is also present on the ventricular side

Aortic valve:

Leaflets are covered by a continuous layer of endothelial cells with a smooth surface on the ventricular side and numerous ridges on the arterial side
The arrangement of the endothelial cells is across, not in line with the direction of flow
The cells are joined to one another by junctions similar to those present on endothelial cells elsewhere in the vascular system
Between the ventricular and aortic surfaces, there are up to five layers of connective tissue: lamina ventricularis, lamina radialis, lamina spongiosa, lamina fibrosa and lamina arterialis (nomenclature of Gross and Kugel)
Within the connective tissue, the elastic and collagen fibers are mechanically coupled to each other in a well defined honeycomb or sponge-like structure
The arterial layer contains coarse bundles of circumferential collagen fibers, which form the macroscopic folds parallel to the free edge of the leaflets
It is this arrangement of fibers that transfers the load of the leaflets to the wall of the aortic root
Between the extracellular components reside interstitial cells designated myofibroblasts, with characteristics of fibroblasts and smooth muscle cells

Microscopic (histologic) images

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Tricuspid valve

Annulus of the pulmonary root

Section through the pulmonary root

Posterior mitral leaflet

Section through aortic root

IHC of aortic valves

Electron microscopy description

Electron microscopy demonstrates that endothelial cell layers are bordered by a basal membrane
Endothelial cells either interdigitate or overlap
They are further characterized by pinocytic vesicles, indicating an active transport system
In the subendothelial reticular tissue, collagenous fibrils are scanty, but fibroblasts are common
The lamina fibrosa consists of tight bundles of collagenous fibrils
Fibroblasts lying among these fibrils show multiple long processes

Electron microscopy images

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Annulus tissue

Commissure tissue

Arrangement of collagenous fibrils

Additional references

Saudi Med J 2004;25:1176, Heart 2000;84:670, Philos Trans R Soc Lond B Biol Sci 2007;362:1421

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