AT, adipose tissue E, elastic fiber

EC, elastic cartilage MG, mucous gland

SE, stratified squamous epithelium

Fibrocartilage is a combination of dense connective tissue and cartilage. It has a matrix with large bundles of type I collagen in addition to type II collagen. The amount of cartilage varies, but in most locations the cartilage cells and their matrix occupy a lesser portion of the tissue mass. Fibrocartilage is found at the intervertebral discs, the symphysis pubis, the knee joint, the mandibular joint, the sternoclavicular joint, and the shoulder joint. It may also be present along the grooves or insertions for tendons and ligaments. Its presence is associated with sites where resilience is required in dense connective tissue to help absorb sudden physical impact, i.e., where resistance to both compressive and shearing forces is required in the tissue. Histologically, fibrocartilage appears as small fields of cartilage blending almost imperceptibly with regions of dense fibrous connective tissue. It is usually identified by the presence of aggregates of rounded cartilage cells (isogenous groups) among bundles of collagen fibers and by the basophilic staining of the capsular matrix material and territorial matrix secreted by these cells. No perichondrium is present.

Figure 1, intervertebral disc, human, Mallory's trichrome x160.

This is a low-magnification view of fibrocartilage. The Mallory method stains collagen light blue. The tissue has a fibrous appearance, and at this low magnification the nuclei of the fibroblasts (F) appear as small, elongate or spindle-shaped bodies. There are relatively few fibroblasts present, as is characteristic of dense connective tissue. The cartilage cells (C) are more numerous and exhibit close spatial groupings, i.e., isogenous groups. Some of the cartilage cells appear as elongate clusters of cells, whereas others appear in single-file rows. The matrix material immediately surrounding the cartilage cells has a homogeneous appearance and is, thereby, distinguishable from the fibrous connective tissue.

Figure 2, intervertebral disc, human, Mallory's trichrome x700.

This figure shows the area circumscribed by the rectangle in Figure 1 at higher magnification. The cartilage cells are contained within lacunae (arrows), and their cytoplasm stains deeply. The surrounding cartilage matrix material is scant and blends into the dense connective tissue. Cartilage matrix material can be detected best by observing the larger group of cartilage cells at the left of this figure and then observing this same area in Figure I. Note the light homogeneous area around the cell nest in the lower-power view. This is the region of cartilage matrix. At the greater magnification of Figure 2, it is possible to see that some of the collagen fibers are incorporated in the matrix, where they appear as wispy bundles.

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