Remember the time you fell off your bike or bumped your head on a sharp corner?
Childhood injuries are things we'd often like to forget,
but our bodies often carry the memories in the form of scars.
So what are these unwanted souvenirs and why do we keep them for so long
after that unintended vacation to the emergency room?
The most common place we see scars are on our skin,
a patch that looks slightly different from the normal skin around it.
Often, this is considered an unfortunate disfigurement,
while other times, deliberate scarification has been used
in both traditional and modern cultures, to mark a rite of passage
or simply for aesthetic decoration.
But the difference isn't only cosmetic.
When we look at healthy skin tissue under a microscope,
we see the cells that perform various functions
connected by an extracellular matrix, or ECM.
This is composed of structural proteins, like collagen,
secreted by specialized fibroblast cells.
Well-arranged ECM allows for transportation of nutrients,
cell-to-cell communication, and cell adhesion.
But when a deep wound occurs, this arrangement is disrupted.
During the process of wound healing, collagen is redeposited at the wound site,
but instead of the basket-weave formation found in healthy tissue,
the new ECM is aligned in a single direction,
impeding inter-cell processes, and reducing durability and elasticity.
To make matters worse,
the healed tissue contains a higher proportion of ECM than before,
reducing its overall function.
In the skin, the overabundance of collagen interferes with its original functions,
like producing sweat,
controlling body temperature
and even growing hair.
The scar tissue is fragile, sensitive to changes in temperature and sensation,
and should be kept in moist environments to maximize healing.
This presence of excessive fibrous connective tissue in an organ
is known as fibrosis, and if that term sounds familiar,
it's because our skin is not the only organ vulnerable to scarring.
Cystic fibrosis is a genetic disorder that causes scarring of the pancreas,
while pulmonary fibrosis is a scarring of the lungs,
resulting in shortness of breath.
Scarring of the heart and the buildup of ECM following a heart attack
can inhibit its beating, leading to further heart problems.
What's common to all these conditions
is that although it retains some of the original functions,
the scar tissue formed after a wound
is inferior to the native tissue it replaces.
However, there is hope.
Medical researchers are now studying what causes fibroblast cells
to secrete excessive amounts of collagen
and how we can recruit the body's other cells
in regenerating and repopulating the damaged tissue.
By learning how to better control wound healing and the formation of scar tissue,
we can utilize the multi-billion-dollar budgets
currently used to address the aftermath of wounding
in a much more efficient manner,
and help millions of people live better and healthier lives.
But until then, at least some of our scars
can help us remember to avoid the sorts of things that cause them.