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Fibrous Skeleton & Valves

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The non-contractile role of the fibrous skeleton is to provide a rigid framework for the valves and an insulating barrier separating atrial and ventricular muscle fibers.

A microscopic view of the fibrous skeleton of the heart at medium magnification (100x) stained with Masson's trichrome. The dense network of blue-stained collagen fibers contrasts with the red-stained cardiac muscle tissue, illustrating the structural support around the heart valves.
Figure 1 A microscopic view of the fibrous skeleton of the heart at medium magnification (100x) stained with Masson’s trichrome. The dense network of blue-stained collagen fibers contrasts with the red-stained cardiac muscle tissue, illustrating the structural support around the heart valves.

At medium magnification (100x) with Masson’s trichrome stain, the fibrous skeleton of the heart appears as a dense network of collagen-rich connective tissue. At this magnification, you may also notice the transition between the fibrous skeleton and adjacent cardiac muscle fibers, which stain a rich red, contrasting sharply against the blue-stained collagen.

In the stain, the abundant collagen fibers are stained blue, making them stand out clearly from the surrounding cardiac muscle tissue. Scattered within the collagen are a few elongated fibroblast nuclei, seen as small, dark purple ovals.

Close-up view of the fibrous skeleton of the heart, highlighting dense, blue-stained collagen fibers with scattered dark purple fibroblast nuclei, observed at medium magnification (100x) using Masson's trichrome stain.
Figure 2: Blue-stained collagen fibers of the fibrous skeleton of the heart. Fibroblasts and scattered among the randomly arranged collagen.

The collagen bundles appear thick and wavy, packed tightly together, reflecting their strength and resilience in anchoring the cardiac valves.

Cross-section of the fibrous skeleton of the heart stained with Masson's trichrome at medium magnification, showing blue collagen fibers interspersed with dark purple fibroblast nuclei and adjacent red cardiac muscle tis
Figure 3: This valve is an extension of the fibrous skeleton. Along with the blue-stained collagen bundles, wavy, purple stained lines represent elastin fibers.

Heart, ventricle, H&E, 40X  Slide 098-1 Right heart wall, H&E, 40X
All by University of Michigan Histology, licensed under CC BY-NC-SA 3.0.

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