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Collagenous (Fibrous) Types
Most dense, regular connective tissues are fibrous types constructed of collagen fibers. Fibrous connective tissues include most tendons, ligaments, and aponeuroses(wide, flat tendons). Dense regular fibrous connective tissue is also an important component of the connective tissues forming periosteum, perichondreum, perineurium and perimysium. Dense, regular arrays of collagen provide linear, inelastic resistances to forces placed across these structures.
Take a look at a fibrous tendon!
|Notice the nuclei of fibroblasts squeezed and flattened in rows between the collagen fibers. Edges of these fibers are difficult to resolve and the elongate nuclei can be mistaken for those of smooth muscle. However, the "box car" arrangments of nuclei between the fibers is a key characteristic for dense, regular fibrous connective tissue.|
Tendons and ligaments are typically described as fibrous or elastic types and a false impression can follow there are no variations. In reality, fibrous tendons and ligaments possess elastic fibers and it is likely elastic tendons and ligaments possess collagen fibers. All tendons are elastic to a certain degree due to some elastic fibers and an undulating arrangment of collagen fibers. In body locales where stretch is a requirement, more elastic fibers occur and where maximal stretch is a requirement, the majority of fibers in a tendon are of the elastic type.
Dense Regular Elastic Connective Tissue
Those tendons and ligaments of the body that require strength and stretch capabilities are constructed of primarily elastic fibers. Some tendons and ligaments attaching to the vertebrae in the neck region are of this type. Remember, elastic fibers are smaller in diameter than those of collagen. Although longitudinal sections of fibrous and elastic tendons can be confused, an examination of these tendons in cross section shows obvious size differences .
|In this side by side comparison of fibrous and elastic tendons cut in cross-section, the relative sizes of fibers is compared. Notice how large and robust the collagen fibers are compared to the smaller elastic types. Nuclei of fibroblasts visible along the edges of fibers are a good indicator these are tendons in cross-section.|
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