Injury

• 1. Introduction

  ›

  Injury is physiological damage to living tissue, and it does not belong to humans alone. A wound can open in a person, in an animal, or in a plant. The same threat runs through all of them: a sharp tooth, a blunt blow, a burst of heat or cold, a dose of venom. What happens next is the strange part. Tissue that has just been torn open begins, almost immediately, to fight back. Across the living world, an injured body releases substances to seal the breach. It limits the loss of fluids. It blocks the entry of bacteria and other pathogens. How does a body know it has been wounded? Why do creatures as different as a plant, a worm, and a person reach for so many of the same defenses? And what happens at the smallest scale, inside a single cell, when the damage becomes too great to mend?

• 2. A Universal Threat

  ›

  Teeth and blunt objects are only the start of the list. Injury can be caused mechanically by penetration with sharp objects, but heat, cold, venoms, and biotoxins all damage tissue too. The causes cut across the boundaries we usually draw between living things. A burn, a poisoning, a freezing: each is a way of harming flesh or leaf alike. Substances released after a wound serve a shared purpose across both plants and animals. They help to occlude the wound, holding in fluids and keeping pathogens out. Many organisms go further and secrete antimicrobial chemicals that limit infection at the wound itself. Regrowth is the other common thread. Both plants and animals carry mechanisms that can result in complete or partial healing over an injury, and even individual cells can repair damage to a certain degree.

• 3. How Animals Mend

  ›

  Mechanical damage to anatomical structure is one definition of injury in animals, but the word carries a wider meaning. It stretches to physical damage of any cause, including drowning, burns, and poisoning. The sources of that harm are the rough business of living: attempted predation, territorial fights, falls, and abiotic factors that have nothing to do with another creature at all. Inflammation is the opening move of the animal response, and it appears in animals of many different phyla. That inflammation prompts the blood or body fluid to coagulate, which is then followed by wound healing. The speed varies. In the cnidaria, healing can be rapid, while arthropods are able to repair injuries to the cuticle that forms their exoskeleton to some extent. Antimicrobial peptides are the chemical weapon many of these animals share. They are produced to fight off infection following an injury by creatures across several phyla, including annelids, arthropods, cnidaria, molluscs, nematodes, and vertebrates.

• 4. The Medicine Of Wounds

  ›

  Medicine has studied injury in humans extensively because of its importance. Much of medical practice is devoted to treating it, including emergency medicine and pain management. The scale of the problem invited an attempt to organize it. The World Health Organization developed a classification of injuries in humans, sorting them by categories that include the mechanism, the objects or substances producing the injury, and the place of occurrence. The categories reach into circumstance and motive as well, covering the activity a person was engaged in when injured and the role of human intent. Physical harm is not the only kind injury can inflict. Injuries can also cause psychological harm, including post-traumatic stress disorder.

• 5. Wounds In Plants

  ›

  Herbivores open many of the wounds a plant will ever suffer. Injury in plants results from the eating of plant parts by herbivorous animals, including insects and mammals. Damage to tissues by plant pathogens such as bacteria and fungi is a second source, and these pathogens may gain entry after herbivore damage or in other ways. Abiotic forces do the rest. Plants are injured by heat, freezing, flooding, lightning, and pollutants such as ozone. A plant cannot flee any of this, so it answers chemically and structurally. It signals that damage has occurred, then secretes materials to seal off the damaged area. It produces antimicrobial chemicals of its own, and in woody plants it regrows over the wounds.

• 6. When A Cell Breaks

  ›

  Cell injury is a variety of changes of stress that a cell suffers due to external as well as internal environmental changes. The triggers are broad. Among other causes, the damage can be physical, chemical, infectious, biological, nutritional, or immunological. Whether a cell survives depends on how far it is pushed. Cell damage can be reversible or irreversible, and depending on the extent of the injury, the cellular response may be adaptive. Where it is possible, homeostasis is restored. There is a line past which repair fails. Cell death occurs when the severity of the injury exceeds the cell's ability to repair itself. That outcome is relative to both the length of exposure to a harmful stimulus and the severity of the damage caused.