Connective Tissue Fibers

Fibroblasts produce three types of connective tissue fibers: collagenous fibers, elastic fibers, and reticular fibers. Of these, collagenous and elastic fibers are the most abundant.

Collagenous (kol-lajce-nus) fibers are thick threads of the protein collagen, which is the major structural protein of the body. Collagenous fibers are grouped in long, parallel bundles, and they are flexible but only slightly elastic (fig. 5.16). More importantly, they have great tensile strength—that is, they can resist considerable pulling force. Thus, collagenous fibers are important components

Elastic fibers

Collagenous-fibers

Elastic fibers

Collagenous-fibers

Falsely colored scanning electron micrograph of collagenous fibers (here yellow) and elastic fibers (here blue) (4,100x).

ure 5.16

Figure

Falsely colored scanning electron micrograph of collagenous fibers (here yellow) and elastic fibers (here blue) (4,100x).

of body parts that hold structures together, such as ligaments (which connect bones to bones) and tendons (which connect muscles to bones).

Tissue containing abundant collagenous fibers is called dense connective tissue. Such tissue appears white, and for this reason collagenous fibers of dense connective tissue are sometimes called white fibers. Loose connective tissue, on the other hand, has sparse collagenous fibers. Clinical Application 5.1, figure 5.17, and table 5.5 concern disorders that result from abnormal collagen.

"Clinically proven, antiaging collagen cream retexturizes skin, making it more resilient, and looking younger!" proclaims the advertisement that seems too good to be true. It is. Although any moisture on dry skin may temporarily improve its appearance, collagen molecules are far too large to actually penetrate the skin. The only thing a collagen cream is sure to affect is your wallet.

Elastic fibers are composed of bundles of microfibrils embedded in a protein called elastin. These fibers branch, forming complex networks in various tissues. They are weaker than collagenous fibers but very elastic. That is, they are easily stretched or deformed and will resume their original lengths and shapes when the force acting upon them is removed. Elastic fibers are common in body parts that are normally subjected to stretching, such as the vocal cords and air passages of the respiratory system. Elastic fibers are sometimes called yellow fibers, because tissues amply supplied with them appear yellowish (see fig. 5.16).

Surgeons use elastin in foam, powder, or sheet form to prevent scar tissue adhesions from forming at the sites of tissue removal. Elastin is produced in bacteria that are genetically altered to contain human genes that instruct them to manufacture the human protein. This is cheaper than synthesizing elastin chemically and safer than obtaining it from cadavers.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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