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Our bodies can repair quite a number of injuries very well. However, it takes time. For larger wounds, complete recovery can last many weeks. Why is this time so long, what is the most important limiting factor? The speed of cell division? I thought cell division was faster, and if necessary, cells could also be transported in the blood stream. Thrombocytes, as far as I know, are transported to the location of the emergency by the blood, and are not produced locally.

If the pure physics and chemistry allowed, for example, a 2x faster healing rate, wouldn't there be any evolutionary pressure for it?

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    $\begingroup$ The limiting problem is the formation of new tissue. New cells could indeed be produced faster, but forming tissue requires much more than just cells. It requires extracellular matrix to provide attachment for new cells, collagen and various other intercellular fluid components (which are secreted by fibroblasts), migration of cells. And bear in mind all of this isn't done on an open end, it needs to be done without actually at any point breaking the blood circulation system or other boundaries between tissue compartments. $\endgroup$ – Armatus Oct 8 '14 at 19:34
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    $\begingroup$ One reason is simply "scale". The healing recovery is taking place on a molecular scale, and it involves a huge number of very, very tiny things. How long does it take to place all of the bricks in a brick wall (for a trivial analogy)? $\endgroup$ – user2338816 Oct 10 '14 at 0:12
  • $\begingroup$ Do you want speed, or accuracy. Uncontrolled cell growth is CANCER. We do not want cells growing extra fast or it is cancer. Also, it takes time to correctly sequence dna strands. Do you want fast healing with lots of scars, extra skin, some new limbs and extra tumors. It takes time to form correct cells. $\endgroup$ – Gordon Davis Jan 14 '18 at 18:50
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The process of wound healing is pretty complicated and is much more than only cell division. The woundhealing process starts almost immediately in the moment of the injury and depending on the injury can take quite a long time. Have a look at the figure below (from the second reference), which shows the phases:

enter image description here

Basically this can roughly be diveded into four phases:

  1. Hemostasis/Coagulation:

    • vascular constriction (blood vessel contraction)
    • platelet aggregation, degranulation, and fibrinformation (formation of a thrombus and closure of the wound)
  2. Inflammation:

    • neutrophil infiltration
    • monocyte infiltration and differentiation into different kinds of macrophages
    • lymphocyte infiltration
  3. Proliferation:

    • re-epithelialization
    • angiogenesis (formation of new blood vessels)
    • collagen synthesis (formation of new connective tissue)
    • formation of the extracellular matrix
  4. Remodeling:

    • collagen remodeling
    • vascular maturation and regression

This process takes some time and can be prolonged when a wound is infected. So I don't think there is much room to speed this up, as you need to go through all these phases. This process is also the result of extensive evolutionary processes; otherwise, such complex cooperation between different cells is not possible. For more details on the process itself, have a look at the references.


References

  1. Factors affecting wound healing.
  2. Cellular aspects of wound healing.
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    $\begingroup$ +1 just for HIPR. You imply it, but it might be worth stating out right that remodeling is most likely to be the rate limiting step (to answer directly) $\endgroup$ – Atl LED Oct 9 '14 at 2:34
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    $\begingroup$ Thats possible. If there is no additional infection. Although this is not really "rate limiting" but takes time to clear. $\endgroup$ – Chris Oct 9 '14 at 5:39
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The time needed for a wound to heal is related to the type of tissue injured and the amount of tissue that needs to be 'reconstructed.' Cell division rates are also a factor.

Healing is a complex process that involves multiple stages.

  1. The body has to limit the damage that can result from an injury. So, first it tries to stop the bleeding and then a local inflammatory process is triggered. This inflammation will:

    • stop pathogens from entering the systemic circulation
    • 'clean' the injured tissue by removing dead cells
  2. In order to recreate the tissue, there is the need for blood which will deliver nutrients and other factors. So, fibroblasts and endothelial cells migrate in the wounded area and form temporary tissue and new blood vessels; the new tissue is called granulation tissue.

  3. The granulation tissue allows for the formation of definitive tissue. This is the remodelling phase. Depending on the wound, the tissue that grows can either be the same as the original one or be fibrous scar tissue.

Looking at the time required by each of these steps:

  1. should be the fastest as it relies on blood cells and factors that are already present in blood. Also, the wound itself will stimulate the local production of some cells/factors involved (inflammatory factors, vasodilator, vasoconstrictor factors.)

  2. and 3. depend on the duration of cell-division processes, extracellular matrix formation, and vascularization. Cell division time can be slowed down by a lack of required nutrients and/or substances. While the granulation tissue forms in almost constant time no matter the injury, the final tissue depends on what type it will be. One simple example is bone tissue versus skin.


References & Links:

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    $\begingroup$ While it's a good answer in describing how the healing of wounds works, most of this I already found on Wikipedia and other sources. I'm still curious about what actually causes it to have this speed? What physical or chemical processes are most responsible that a certain step takes 8 days instead of 8 hours? $\endgroup$ – vsz Oct 9 '14 at 14:33
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I claim that one great limitation in our understanding of the healing process is that biologists have no understanding of the progression of disease or infection, that not enough time may be given for the body to recover, and that doctors might not understand how to help their patients recover from disease or infection. Each patient is different, and personalised recovering plan is often important. So, too few resources — e. g.: the time of a doctor and/or a nurse — are offered to patients, so doctors have little time to build their understanding of the disease or injury with which their patients are dealing. It is the patient who makes himself or herself able to recover. But, without understanding, the recovery process is not optimal.

Healing from upper respiratory infection:

I will give one example in LOR Medicine. Upper respiratory infections are one of the most common infections and most expensive diseases in society. One reason is that people do not understand:

  • how to recover from disease
  • how long the common cold or flu lasts (doctors underestimate the time that it will take for their patients to heal very often.)

In nursing school, they teach students how to, among other things:

There is no way to measure what the correct course of treatment is for any given patient during the course of, for example, an upper respiratory infection. Nurses ask the patient when he or she feels their best and adjusts treatment accordingly. So, good communication is essential in nursing.

Wound healing:

Chris and Cornelius cover some of the basic cellular processes of wound healing. However, some big steps are still missing in regards to healing.

The primary healing of wounds is aided by:

  • adequate wound-edge coaptation
  • healing without complications
  • minimal scar tissue

through the cellular processes of wound healing described by Cornelius and Chris.

Secondary healing of wounds is characterized by:

  • wound tissue left exposed (open)
  • defect filled with granulation tissue
  • surface covering the epithelium
  • less functionality
  • possible thermal and mechanical injuries

Embryological and biochemical aspects of tissue healing

I cover here some growth factors. If they are not present, then their absence will surely be a limitation to the healing process.

  • TGF - transforming growth factor
  • MDGF - macrophage-derived growth factor
  • HB-ECG - heparin-binding epidermal growth factor

Here are some other factors:

  • bFGF - basic fibroblast growth factor
  • KAF - keratinocyte-derived growth factor

Special cytokines for inflammation may later come into play.

Sources

  1. Human skin wounds: a major and snowballing threat to public health and the economy. Sen C.K., Gordillo G.M., Roy S., Kirsner R., Lambert L., Hunt T.K., Gottrup F., Gurtner G.C., Longaker M/T. Wound Repair Regen. 2009 NovDec;17(6):763-71.
  2. My notes during 4 years of nursing
  3. My notes during classes of Surgery
  4. My notes of Embryology and Surgery about the growth factors
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  • $\begingroup$ Once again: Why the downvotes without explanation? Answers can only get better with some explanation what can/should be done. $\endgroup$ – Chris Oct 9 '14 at 5:39
  • $\begingroup$ @Chris : While I didn't vote on this answer yet, I guess it's because it is about why medics cannot treat wounds faster. The question was about the biological process itself, and not why we don't have the technology to speed it up. $\endgroup$ – vsz Oct 9 '14 at 14:35
  • $\begingroup$ @vsz: That would be a perfect comment on this topic. $\endgroup$ – Chris Oct 9 '14 at 16:00
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    $\begingroup$ I think the challenge of the case is that the main question is open and asks much more than some processes. Your body then again explains much more narrower thing about biological level. The answer should be adequate to the question in title - not only textbook answer and/or simplification what can be found in books and/or review articles. Simplification is NOT enough for practical purposes. The body is user's attempt to answer it so well as possible. Biology is not only about one process. It is a multidisciplinary field with limitations. $\endgroup$ – Léo Léopold Hertz 준영 Oct 9 '14 at 19:29

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