Re: News: Carbon dating shows humans make new heart cells.

On Apr 6, 8:07 am, "Steven L." <sdlit...@xxxxxxxxxxxxx> wrote:
Ye Old One wrote:
Carbon dating shows humans make new heart cells

http://www.nature.com/news/2009/090402/full/news.2009.232.html

The cold war helps settle a hot debate about how hearts grow.

Monya Baker

Fallout from nuclear bomb tests during the cold war has just yielded
encouraging news for those searching for ways to reverse heart
disease.

A team led by Jonas Frisén from the Karolinska Institute in Stockholm
has shown that adult human hearts make new muscle cells, albeit very,
very slowly1.

I fail to be surprised by this.  After all, the liver can regenerate
quite quickly--cut off half the liver and the other half can regenerate
into a full liver in a relatively short time, probably from stem cells
residing in the liver.

What surprises me is why this does not happen in other organs like the
heart.  Why did we humans evolve to have a regenerative liver, and (of
course) regenerative skin--but not a regenerative heart?  Evidently this
is true in other mammalian species.  Is it also true for non-mammalian
species?

There are really two questions here. In addition to the one you ask
-- why don't all organs regenerate? -- there is also -- what is the
difference between organs that do and organs that don't? That is,
there is the teleological question of why and the mechanistic question
of how.

The second question now is starting to get some answers. Look at
"Stem cell research sheds light on organ regeneration" at
http://www.news.harvard.edu/gazette/2007/02.22/05-pancreas.html

or, for a different take on things (and another reference to check)
look at our own Larry Moran's blog "What Controls Organ Regeneration?"
at
http://sandwalk.blogspot.com/2007/05/science-questions-what-controls-organ.html

The why question is always a problem in biology, trying to decipher
reasons why evolution took one turn instead of another. Of course,
organs subject to damage and wear and loss, like blood and skin and
gut and liver, get replaced. Liver is on the list because all
chemicals absorbed into the body from digestion go directly there
before entering the general bodily blood stream (through the hepatic
portal vein). Plants produce a lot of toxic stuff to try to get you
not to eat them so the liver is what takes the brunt of damage caused
by all the really bad chemicals you ingest. Pancreas and heart and
brain are rather well protected. Something that damages them is going
to be some really horrific injury and you are probably already dead
anyway. Besides, actively growing cells are subject to mutation and
cancer so it is best to keep them to a minimum. That is the type of
handwaving, just-so story that is usually invoked.

.

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