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## Lines of Cleavage and Stretch Marks The majority of the collagen and elastic fibers in the skin are oriented in parallel bundles at specific body locations. The alignment of fiber bundles within the dermis is a result of the direction of applied stress during routine movement; therefore, the fun...

## Lines of Cleavage and Stretch Marks The majority of the collagen and elastic fibers in the skin are oriented in parallel bundles at specific body locations. The alignment of fiber bundles within the dermis is a result of the direction of applied stress during routine movement; therefore, the function of the bundles is to resist stress. Lines of cleavage *tension lines* in the skin identify the predominant orientation of collagen fiber bundles *figure 6.7*. These are clinically and surgically significant because any procedure resulting in a cut perpendicular to a cleavage line usually will be pulled open as a result of the recoil resulting from cut elastic fibers. This often results in slow healing and increased scarring. In contrast, an incision made parallel to a cleavage line usually will remain closed. Therefore, surgical procedures should be planned to consider lines of cleavage, thus ensuring rapid healing and prevention of scarring. Together, collagen fibers and elastic fibers contribute to the visible physical characteristics of the skin. Whereas the collagen fibres impart tensile strength, elastic fibers allow some stretch and recoil in the dermis during normal movement activities. Stretching of the skin that may occur as a result of excessive weight gain or pregnancy often exceeds the elastic capabilities of the skin. When the skin is stretched beyond its capacity, some collagen fibers are torn and result in stretch marks, called *striae* *stri'ē; stria = furrow*. Both the flexibility and thickness of the dermis are diminished by effects of exposure to ultraviolet light and aging, causing either sagging or wrinkled skin. ## Clinical View 6.2: Tattoos Tattoos are permanent images produced on the integument through the process of injecting a dye into the dermis. The dermis doesn’t have a rapid cell turnover, so the injected dye remains in this area for a long time. Scar tissue surrounds the dye granules, which are too large for dendritic cells to ingest, and they become a permanent part of the dermis layer. It is usually impossible to completely remove a tattoo, and some scarring may occur. Older methods include *excision* *cutting out the tattoo, sanding down the tattooed skin*, and *cryosurgery* *freezing the area of tattooed skin prior to its removal*. Lasers are now used in some cases to break down the tattoo pigments. Newer tattoo inks have been introduced that allow for easier tattoo removal. ### What Did You Learn? 5. Compare and contrast the papillary versus reticular layer of the dermis, with respect to their tissue type and the structures they contain. 6. What is indicated by the lines of cleavage in the skin, and why is this medically important? The image shows a human figure drawn in purple lines. The purple lines represent the lines of cleavage. There are two zooms in on the image. One shows an incision perpendicular to the lines of cleavage. The text states that this can gape and delay healing. The second image shows a similar incision, but this time parallel to the lines of cleavage. The text states that this incision is more likely to heal quickly and not gape open.