(orchestra music)
- Hello and welcome to Brain Stuff.
Today's question, does your
body really replace itself
every seven years?
The short answer is no.
But don't worry, this isn't a case of
chicanerous researchers pulling the wool
of shoddy science over your eyes.
Your body mostly replaces
itself every seven to 15 years.
Some bits are never replaced.
Others like the lining of
your stomach and intestines
are renewed much faster.
Due to the constant wear and tear
from the process of digestion,
these cells have an average
lifespan of just five days.
Yes, the organs that work the hardest
have the fastest changeover.
You get a whole new skin for instance
every two to four weeks.
Your red blood cells survive
less than half the year,
which is not bad
considering that their route
through the circulatory
system is about 1,000 miles.
And your liver renews itself at least once
every couple of years.
As the human body's detoxifier
it goes through a lot.
Other tissues take longer to completely
replenish themselves.
Like your bones.
Skeletal cells die and
new ones grow constantly,
but the process takes about 10 years
and the process slows
down as we get older,
which is why our bones tend
to get weaker as we age.
And like I said, some parts of your body
stay with you for life,
just like heartache.
The cells on the inner lens of your eye
were formed when you were an embryo.
Your tooth enamel wears down with use
never to return.
And evidence indicates that
you can't regrow the neurons
of your cerebral cortex.
Its loss can lead to
diseases like dementia.
Now luckily, other parts
of your brain do regenerate
like the hippocampus, which
helps us create memories
and the olfactory bulb,
which helps us smell.
So how do we know all of this?
Well it turns out it's
all thanks to our old pal
nuclear weapons testing.
Yeah, hi fives for radioactive stuff
being released into the atmosphere.
No really.
Above ground nuclear
detonations during World War II
and the Cold War spiked
the earth's air supply
with extra carbon 14.
It's been declining back toward the norm
at a predictable rate since the 1960s,
which means that you can
use the amount of it present
in any given tissue sample to determine
when those cells were born.
More carbon 14 means older cells.
Well that's all the time we
have for Brain Stuff today,
but if you wanna learn more, head on over
to our stuff about being human playlist.
And if you like this
video, make it official.
And if you're pretty into websites,
check out ours at brainstuffshow.com.
No, but really.
Wait, no, no, yes, no really.
(laughing)
I'm on a rollercoaster.
