Collagen Fibers

Collagen fibers exist almost everywhere in the body; they are the most prevalent type of fiber in connective tissue (collagen type I). They can be clearly identified in histological sections by staining with various acidic dyes. Collagen fibers are unbranched. They consist of collagen fibrils. Most of the fibrils have diameters of 30–70 nm. Collagen fibers with diameters of 2–10 μm of ten form wavy fibers, like undulating lock s of hair.  This figure shows wavy collagen fibers (blue) in connective tissue from the corium ( stratum reticulare of the corium). The connective tissue cells between them are stained red. Collagen (colla, Greek: glue, bone glue) is the prevalent fiber protein in the extracellular matrix.

Stain: azan; magnification: × 200

Collagen Fibrils

In electron micrographs, the collagen fibrils, which are approximately 30–70 nm thick , show a striation pattern of lighter and darker bands (termed cross-striation) with a periodicity of about 6 4 nm and range limits of 50 and 70 nm, respectively. This typical cross-striation is brought about by the arrangement of the 280 nm long tropocollagen , which consists of three poly-peptide chains ( α-triple helix). The tropocollagen molecules are lined up one after another, forming gaps after each molecule. They are also packed one over another in a staggered way. In the process, the protocollagen molecules are shifted by a quarter of their length (parallel aggregation ). This causes the cross-striation seen in microfibrils.

Electron microscopy; magnification: × 52800

Collagen Fibrils

Collagen fibrils with cross-striation as an example of a highly organized biological system.  Tail tendon from a rat.

Electron microscopy; magnification: × 18 000

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgart · New York .