Question: Over the weekend I attempted to make paper cranes. Unfortunately, I got a paper cut. This made me wonder what biological events happen once there is a cut in the skin up until the point the tissue is considered to be fully healed. In this question and answer I wish to follow the wound healing process and investigate the biochemical events that occur.

Answer: When a break in the skin occurs, a rather predictable series of events happen. The body’s first response is to create a seal around the site of injury to prevent foreign matter from entering and causing an infection. The body creates this initial seal by hemostasis, more commonly known as blood clotting. Hemostasis starts with the release of various tissue factors which activate platelet cells in blood. This eventually cascades down and causes the polymerization of fibrinogen into fibrin. Fibrin is used to form the main structure of a blood clot.

The next phase of healing involves inflammation of the affected area. During this phase, immune cells are hard at work killing any foreign bacteria and clearing dead cells surrounding the wound. One biochemical mechanism that immune cells can use to kill bacteria involves inducing the transcription of iNOS. iNOS or induced nitric oxide synthase is an enzyme specific to immune cells that synthesizes nitric oxide; other cells have different types of NOS enzymes. The reason why iNOS is specific to immune cells is that it produces nitric oxide in sufficient quantities to kill most cells unlike other NOS enzymes. Immune cells take advantage of this to kill surrounding bacteria (and other unfortunate nearby cells). This release of nitric oxide is one biochemical mechanism that contributes to the symptoms of inflammation (redness, swelling).

Following the inflammation phase, platelet derived growth factors are released into the surrounding tissue; this signals cell migration and proliferation to repopulate the site of the wound. Over time cells will slowly close the site of the wound and begin to remodel the extracellular matrix back to a healthy pre-wound state.

  • Zeus the Sitar Lord

Sources:

  1. Guo, S., & DiPietro, L. A. (2010). Factors Affecting Wound Healing. Journal of Dental Research, 89(3), 219–229.
  2. Alberts et. al., Molecular Biology of the Cell, 6th Edition
  3. https://en.wikipedia.org/wiki/Wound_healing
  4. https://en.wikipedia.org/wiki/Coagulation
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