Friday, 8 September 2017

How Wounds Heal ....

As I mentioned in my Immune System blog the skin is the first line of defence against invasion from bacteria.  If the skin is broken it will repair itself!  I talked about the different types of wound in my Sick Nursing blog but whatever the injury the healing process will be the same.

There are 3 phases to healing:
·         Regeneration
·         Repair
·         Remodelling

The first 2 phases can occur in one of 2 ways.  The preferred method is called 'first intention' - this is when the edges of the wound are held together and will then quickly stick to each other.  The longer process of healing by 'second intention' is when the wound edges cannot be held together because the wound is too large and too much tissue has been lost.  In this situation the wound has to fill with new tissue before the skin can grow over the top.

The first stage of healing is bleeding - blood will leak from damaged blood vessels into the damaged area.   Platelets in the blood will begin to stick to the area and will activate the fibrin (or fibrinogen) which is found in the plasma of blood.  Together they form a seal over the wound.  As I mentioned in last week's blog inflammation follows as fluid and cells rush to the area.  The white blood cells (polymorphs) will either ingest any bacteria in the wound or will release a substance to liquefy the damaged tissue, which will then be absorbed.  

The second stage - which usually follows after about 30 minutes - is when the damaged area begins to shrink.  The polymorphs continue to work but new blood vessels and tissue cells will move in to replace the clot.  These cells will form a new layer of skin under the scab (clot).  In deeper wounds a similar process will be occurring further into the wound.  

This stage varies according to the tissue damaged :- the epidermis or lining of the gut  regenerates and repairs easily.  Larger wounds will have more tissue which needs replacing and so will take considerably longer to repair.

Cells called fibroblasts move to the area and multiply. As these fibroblasts multiply and produce collagen (which connects skin to underlying organs and also gives muscles etcetera their strength).  it results in strands of fibrin which tissue can be built upon - a bit like scaffolding on a building.  Epithelial cells multiply and use this scaffolding to 'fill' the wound.   Myofibroblasts  cleverly attach to the edges of the wound and contract which causes the wound to shrink in size!

Repair continues with establishing blood flow to the damaged area.  Capillaries which were damaged will produce endothelial cells, these will push their way into the wound and begin to multiply, these form a very basic circulatory system in the damaged area.  In parallel with this a system of lymphatic vessels grow which will 'mop up' any leaks and return them to the circulation system. 

So within a few days the blood clot ,which originally formed just after the wound occurred, will become granulation tissue.  

As the fibroblasts continue to produce connective tissue the number of blood vessels decrease and the white blood cells will disappear.  Nerve fibres will begin to grow back into the area.

The final phase of healing is remodelling, when the collagen realigns and the wound becomes more pliable.  This is when damaged tissue returns to its pre-injury state and when physiotherapy and other types of therapy can help.

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