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5.3.5: Cartilage Tissues

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    53906
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    Cartilage Tissues

    There is only one type of cell in cartilage, chondrocytes. They secrete and maintain the extracellular matrix of the tissue. Chondrocytes arise from mesenchymal stem cells, just like the fibroblasts of connective tissue proper do, but chondrocytes are specialized to produce just cartilage. The extracellular matrix produced by the chondrocytes is so tough and durable, the chondrocytes are in danger of being crushed by it. This is why chondrocytes always leave a region around themselves free of the cartilaginous extracellular matrix that makes up the rest of the tissue. These non-cartilaginous pockets around each chondrocyte are called lacunae and are clearly visible when examining cartilage under the microscope. Cartilage is distinctive compared to other types of connective tissues since the chondrocytes inside lacunae appear similar to a human eye. When examining a type of tissue, if you see an eye-like structure, it is probably a type of cartilage. Lacunae appear similar to the upper and lower eyelids and the white of a human eye and a chondrocytes appear as the iris and pupil of a human eye.

    Figure showing similarities in the shape of a human eye and the shapes of chondrocytes in lacunae.

    Cartilage has mainly collagen and elastic protein fibers and a ground substance rich in the carbohydrate hyaluronan. The carbohydrate hyaluronan (sometimes known as hyaluronic acid or hyaluronate) binds up huge numbers of water molecules in the extracellular matrix of cartilage. This helps solidify the ground substance around the collagen and elastic fibers of cartilage. As a result, it is often difficult to see the protein fibers in cartilage when viewing preparations under the microscope.

    Type of Cartilage

    Features & Locations

    hyaline cartilage (two different stains shown)

    Microscopic images of hyaline cartilage with chondrocytes in lacunae

    Hyaline cartilage is the most prevalent type, forming articular cartilages and the framework for parts of the nose, larynx, and trachea.

    The lack of blood vessels in hyaline cartilage means that nutrients and wastes must diffuse through the tissue, thus limiting the thickness of the hyaline cartilage.

    Top tissue is magnified by 1000x.

    Bottom tissue is magnified by 400x.

    elastic cartilage (two different stains shown)

    Microscopic image of elastic cartilage with chondrocytes in lacunae surrounded by elastic fibers

    Elastic cartilage and its surrounding perichondrium form the cartilaginous, flexible framework in the pinna of the external ear. Elastic cartilage also forms the framework for the epiglottis and several of the smaller laryngeal cartilages.

    Chondrocytes in elastic cartilage are larger and more numerous than in hyaline cartilage and form fewer isogenous groups. The extracellular matrix of elastic cartilage is less abundant than in hyaline cartilage.

    With a special stain, elastic fibers are more readily visible (bottom image).

    Tissues are magnified by 400x.

    fibrocartilage

    Microscopic image of fibrocartilage with chondrocytes in lacunae surrounded by matrix.

    Fibrocartilage, the strongest of the cartilages, blends the strength of dense connective tissue with that of cartilage: obvious collagen fiber bundles (dense connective tissue) and a flexible, non-compressible ground substance (cartilage). Fibrocartilage exists in isolated pockets where extra strength is needed, rather than as an independent cartilage; therefore, it has no perichondrium.

    Fibrocartilage is frequently seen as a transition from dense connective tissue when greater strength is needed, as in the pubic symphysis and the intervertebral discs.

    Fibrocartilage forms a cushion between bones of the knee, where resistance to compression and to forces from multiple directions are needed. Under these conditions, collagen bundles are arranged irregularly, making this type of fibrocartilage easy to confuse with dense irregular connective tissue.

    Tissue magnified by 400x.

    Attributions (All Connective Tissues Sections)


    This page titled 5.3.5: Cartilage Tissues is shared under a not declared license and was authored, remixed, and/or curated by Rosanna Hartline.

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