Re: Inflammation and Evolution
- From: "Bryan Heit" <warthaug@xxxxxxxxx>
- Date: 12 Oct 2005 12:31:24 -0700
You have grossly misunderstood what the purpose of inflammation is.
Inflammation's main role is not to help wounds heal, but rather to
clear infectious agents (mainly bacteria) from your tissues, and to
"clean up" damaged tissues so repair can occur. Generally speaking,
inflammation is largely resolved by the time healing occurs, although
inflammation is involved in the initiation of the healing process. The
inflammatory response is quite complex, and is extremely well evolved
to fullfill its purpose of clearing bacteria. The inflammatory
response to injury is driven by the same mechanisms, and the
inflammation is absolutely required for proper healing to occur.
When you injure a site (or have an infection), pro-inflammatory
molecules are produced at the site of injury/infection. These include
clotting factors, factors released from dead/dying cells, as well as
chemicals produced specifically by immune cells within the
damaged/infected tissues. These signals activate the cells which line
your blood vessels (called endothelium), and in response to this
activation, the endothelium "pulls" immune cells out of your blood and
into the damaged/infected tissue.
The reason your arm became swollen is simple - the process which allows
passage of the immune cells into the site of injury also allows fluid
from the blood to enter the tissue. This increases the amount of fluid
in the tissue, thus resulting in swelling. Swelling has been proposed
to have a variety of biological functions - including immobilization of
the injured site, increased sensitivity to pain (which makes you take
it easy on the injured limb), it may reduce the movement of pathogens
within the tissue, and it also allows for increased concentrations of
blood-born anti-bacterial compounds to enter the tissue.
Once the immune cells are in the tissue they begin to do a variety of
things. Cells called neutrophils run around, gobbling up and killing
bacteria. Other cells, termed monocytes/macrophage, do much the same,
and also clean up dead cells and damaged proteins. Depending on the
type of injury/infection, other cells may also be involved. Once the
wound is sterile, and all the debris cleaned up, these cells begin the
healing process. For example, neutrophils can induce the formation of
new blood vessels, whereas macrophage play a major role in tissue
remodeling. Other cells (notably fibroblasts) are also involved in the
tissue healing process, but as a general rule don't become highly
active until the inflammation is being resolved. Eventually the
inflammation resolves, the immune cells are removed, and tissue repair
hopefully fixes your wound.
As for why you experienced such a prolonged recovery, there are several
possibilities. Firstly, joint injuries are, due to the structure of
joints, slow to heal. This is for several reasons, but notably some
portions of the joint which tend to get injured (i.e. cartilage,
tendons, synovial lining) are not readily accessed by the immune
system. As such cleanup of the damaged tissues is very slow.
Secondly, minor reinjury, from small limb movements, can sow the
healing process by damaging additional tissue. This continual reinjury
will also cause the inflammation to persist. Lastly, joint injuries
are prone to pathological inflammation - which in plain English means
inflammation which doesn't belong there. This is due to a variety of
factors, including the retention of inflammatory molecules within the
synovial fluid of the joint, the tendency of joints to develop
vasculitus, and the difficulty involved in cleaning up cell debris from
what is essentially a fluidic environment.
The course of treatment your doctor recommended (non-movement, icing,
use of an anti-inflammatory) is the best thing you can do - cold
reduces inflammation by restricting blood flow to the region. Mild
anti-inflammatories like naproxen also reduce inflammation, but still
allow the inflammation required for wound healing to occur.
Non-movement is obvious - it prevents additional damage. He was also
correct about the unlikeliness of an infection at the site - any
bacterial infection which would cause the degree of swelling you
describe would also have systemic effects such as fever, or in extreme
cases, even shock.
The second course of action recommended by your doctor was also a good
one, particularly in the case of a slow healing injury (he probably
suspected pathological inflammation, as steroids/surgery are only
beneficial in these cases). Steroids are simply a powerful
anti-inflammatory, and the risk of infection from injection is pretty
much zero (millions of injections are given every year, and infections
are almost non-existent).
Trying to force yourself to walk/use an injured joint is about the
worst thing you can do - additional damage will occur, leading to
increased duration/intensity of inflammation. In addition, long-term
inflammation and repetitive injury can lead to fibrosis (scarring) of
the injury site. Fibrosis is the evolutionary equivalent to triage -
fix the injury at all costs, even if it limits the use of the damaged
site. Scarring is an example of fibrosis.
Bryan
.
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- Inflammation and Evolution
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- Re: Inflammation and Evolution
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- Inflammation and Evolution
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