Cardiovascular disorders

II./1.1.: The fibrous skeleton of the heart (annulus fibrosus)

The heart valves are responsible for maintaining unidirectional blood flow in the heart. The structure of the heart valves can easily be examined at the section made through the fibrous skeleton of the heart (annulus fibrosus) – this section is cut at the level of sulcus coronarius (between the atria and ventricles) – by looking at the valves from the direction of the removed atria (Figure 1.). 4 orifices of the heart can be observed at this section:

- between the atria and ventricles the atrioventricular or venous orifices (ie. the blood flows into the ventricles through these openings; those orifices are the venous 'inputs' of the ventricles, regardless of the blood oxygen content): right and left atrioventricular orifices

- between the ventricles and the large arteries the arterial orifices are situated (ostium of the pulmonary trunk and ostium of the aorta), as the 'outputs' of the ventricles.

Felirat: Figure 1.: The superior aspect of annulus fibrosus (the atria and the great vessels above this plane have been removed)

The left atrioventricular ostium is located most posteriorly, the right atrioventricular orifice can be found on its right side and slightly anteriorly. Between the two venous orifices the aortic ostium is placed and in front of the aorta the ostium of the pulmonary trunk can be seen. The two venous orifices are surrounded by the connective tissue rings formed by the fibrous skeleton of the heart (annuli fibrosi). The arterial orifices have their thick, own walls, made by elastic and collagen fibers thus forming similar fibrous rings. The fibrous skeleton of the heart has two strengthenings named fibrous triangles: the left and right fibrous triangles (trigonum fibrosum dextrum et sinistrum). The right fibrous triangle contains an important opening, the hiatus for the atrioventricular (His) bundle.

The fibrous annuli build a tough structure, thus mechanically separate the atrial and ventricular cardiac musculature (upwards the atrial, downwards the ventricular myocardium originates from it). This separation is not only mechanical but electrical as well: since only the impulses of the atrioventricular bundle can penetrate the fibrous skeleton, the contraction of the atria –with delay- is followed by the contraction of ventricles (systole).

Another important role of the fibrous skeleton is to form an origin for the heart valves, providing a safe fixation for them on the constantly moving heart.

The heart valves can be demonstrated using the pathological procedure as well. In this case, the left and right sides of the heart are opened with scissors making triangular flaps.

Or, using the anatomical demonstration method, „windows” can be opened by removing the anterior wall of the left and right ventricles (approx. 4x4 cm "windows" can be cut).