Skin Self-repairs

close up photograph of a woman with her hand on her back next to a scar

Biological Strategy

Humans

AskNature Team

Image: BLACKDAY / Shutterstock / Some rights reserved

Regulate Cellular Processes

Cells are the basic building blocks of all living systems, so cellular processes dictate how physiological processes occur within those systems. Cells (whether entire unicellular organisms or parts of multicellular living systems) grow, metabolize nutrients (that is, chemically transform them), produce proteins and enzymes, replicate, and move. Cells as part of multicellular systems rarely act alone, instead having ways to signal to start and complete simple to quite complex interactions. How skin heals is a good example of the role of cellular processes. Blood cells called platelets release clotting factors to stop the bleeding; white blood cells rid the area of foreign materials and release molecules to coordinate healing; cells called fibroblasts start rebuilding using proteins called collagen; new blood vessels form; and skin cells called keratinocytes create the new surface.

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Physically Assemble Structure

Living systems use physical materials to create structures to serve as protection, insulation, and other purposes. These structures can be internal (within or attached to the system itself), such as cell membranes, shells, and fur. They can also be external (detached), such as nests, burrows, cocoons, or webs. Because physical materials are limited and the energy required to gather and create new structures is costly, living systems must use both conservatively. Therefore, they optimize the structures’ size, weight, and density. For example, weaver birds use two types of vegetation to create their nests: strong, a few stiff fibers and numerous thin fibers. Combined, they make a strong, yet flexible, nest. An example of an internal structure is a bird’s bone. The bone is comprised of a mineral matrix assembled to create strong cross-supports and a tubular outer surface filled with air to minimize weight.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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Skin of humans self-repairs through an over-lapping sequence of cellular activities.

“When the skin is scraped deeply enough to penetrate the epidermis, the blood vessels in the dermis can be damaged and start bleeding. Platelets in the blood come into contact with collagen and other components of the skin that have been exposed by the injury. This contact induces the platelets to release clotting factors and other substances in order to stop the bleeding. As the bleeding stops, the healing has already started. Special white blood cells called neutrophils than arrive at the site to begin the process of ridding the area of foreign materials, unwanted microorganisms, and damaged tissues. This process is aided by the development of local inflammation, fueled by cytokines, molecules that coordinate subsequent healing.

“Once the wound site has been cleaned out, fibroblasts migrate to the area to start laying down new collagen on the scaffolding of the original clot. The chemical activity occurring at this time is intense, as the fibroblasts at the wound site mature and produce new proteins to speed healing. In order to restore the dermis, different types of collagen are produced at the wound for the next several days. The collagen undergoes continuous remodeling to physically fill in the injured region. Simultaneously, new blood vessels become established in the area. While all this is going on, the epidermis is preparing to repave its surface by moving new keratinocytes to the location of the injury.” (Jablonski 2006:123-124)