SAL KHAN: This is Sal here.
And I'm at Stanford Medical School
with Dr. Andy Connolly, who's a pathologist here.
And this is the second in our series
on looking at some of these slides.
ANDY CONNOLLY: Yeah.
So we left off last time, Sal, looking at this piece
here, which is normal colon.
We had said this is an example of what you'd
see at the edge of a specimen released for colon cancer.
Now I'm going to click to the next one, which
is a slightly more worrisome area if you're
a pathologist looking through the colon.
And so I'm going to zoom in just a little bit here
to take a look at these.
SAL KHAN: Looks very worrisome compared to the last one.
ANDY CONNOLLY: And so what we don't
like about it is we saw before this
is what the normal gland looks like.
It's a test tube shape and down, and it
has these cells which are normal.
Now all of a sudden it looks a little thicker here,
and what catches our eye also is these aren't just
straight test tubes anymore.
They divide.
They kind of go in and out like that.
SAL KHAN: But they still are test tubes.
Following up what we said in the last video
is that they just look like circles as opposed
to test tubes because we're taking a cross-section,
because they're kind of popping out of the two dimensions.
ANDY CONNOLLY: That's right.
But although, when you come from the surface here
and you go down, they normally should never branch.
SAL KHAN: I see.
ANDY CONNOLLY: And so these ones are branching,
and that's always bad.
And then you can see the way-- when
you're putting a cross-section, there's
normally just a little hole in the middle.
And that's where the mucin-- you can even see it
spilling out there.
SAL KHAN: Wow.
You can.
ANDY CONNOLLY: So you can see it just kind
of coming right out of there.
This one here looks different.
And what it is, it's piled up.
And so it's a little bit bigger around.
And in order for these cells, more cells--
they're going to be all piled up and going like this,
and they even branch.
And so what this is, is that we look
a little more closely at this piece.
And we say, hmm, I wonder if that's cancer.
Could it be pre-cancer, or is this just
an area of irritation?
And a common response of the body to irritation
is some sort of change.
And like we were saying before, epithelium is the top layer.
SAL KHAN: Right, right.
The stuff that's facing the outside world.
ANDY CONNOLLY: Facing the outside world.
So if it's irritated, often the epithelium will change.
And in this case, it's changing by undergoing more growth.
SAL KHAN: Is it always-- even if it's non-cancerous,
is it going to be a higher likelihood that it's
going to become cancerous in the future?
ANDY CONNOLLY: A lot of cancers, it appears,
in the body come from parts of the body that are either
irritated or have some sort of environmental challenges
that are constantly at them.
And part of that is because there's a lot of cell division.
SAL KHAN: I see.
ANDY CONNOLLY: If you keep dividing a cell,
you might have errors in the DNA.
SAL KHAN: So that's why skin cells, bowel cells--
ANDY CONNOLLY: That's right.
And even things like liver.
If you keep damaging your liver, you
might have ongoing things and liver cancer.
So when you're looking here, the pathologist
would look at this area and say, well, it's
a dividing gland that's kind of thrown up in these areas.
But largely, they're still making mucin
or they're this type here, which looks like it's tall
and probably absorbing water.
SAL KHAN: I see.
So even within these test tubes-- well,
they're not really test tubes.
But inside of these vessels, there
are also still the absorptive cells as well.
ANDY CONNOLLY: That's right.
So here, we would sign this off as hyperplasia.
SAL KHAN: Hyperplasia.
So hyper, like too much of something.
ANDY CONNOLLY: Yes.
SAL KHAN: And plasia?
ANDY CONNOLLY: Growth.
SAL KHAN: See.
ANDY CONNOLLY: And so plasia just means growth.
And so hyperplasia means too much growth.
But the important thing is if you took away the irritant,
it wouldn't do this.
SAL KHAN: I see.
ANDY CONNOLLY: So if you took away
whatever the irritant is for the hyperplasia,
it would go back to being normal.
SAL KHAN: I see.
I see.
And that's just something we know.
ANDY CONNOLLY: That's right.
SAL KHAN: There's some stimulus that
was causing these cells to do that.
It might have been diet, might have been some chemical.
It could have been just--
ANDY CONNOLLY: We're never really sure
what, because so much of it is things
that just float on through.
So it's really hard to know.
But, yeah, this is probably too much growth in response
to an irritant.
SAL KHAN: So it's possible that it just
happened to be when this section of the colon was taken out.
If this was done a day later maybe,
then maybe this might have not been there?
ANDY CONNOLLY: Yeah, probably take longer than that.
A couple weeks.
SAL KHAN: A couple weeks, but it's--
ANDY CONNOLLY: Because what happens
is that the cells come from the bottom,
and they work their way up towards the top.
And so eventually the top would behave--
SAL KHAN: And so the way the body works here--
and it's kind of like the skin-- is this as constant.
These cells are being used up, because things
are kind of scraping by them.
And they get a lot of use.
ANDY CONNOLLY: They do.
And in fact, there's a lot known now about stem cells.
And the stem cells for the intestine are these guys.
SAL KHAN: Oh, wow.
So how do you differentiate the stem cell versus--
ANDY CONNOLLY: At the very bottom, the bottom hemisphere,
there are going to be cells there
that do not have the open chromatin
and kind of elongated.
SAL KHAN: I see.
ANDY CONNOLLY: There may be ones which
are endocrine cells, meaning they release hormones.
And so they may have hormone-releasing cells.
But in this bottom hemisphere, that
turns out to be where the intestine keeps them.
And these guys are probably the stem cells.
SAL KHAN: And stem cells are cells
that haven't picked their jobs yet.
ANDY CONNOLLY: They haven't, and so there's
all kinds of stem cells.
There's the stem cell that can make a whole body, being.
But then there's also the kind that
can make the rest of the colon.
SAL KHAN: I see.
ANDY CONNOLLY: And so this one is probably
the stem cell they can make the rest of the epithelium,
but these two different kinds.
SAL KHAN: The two different types, right.
ANDY CONNOLLY: So they're down here at the bottom.
That's about where you'd want them.
SAL KHAN: Exactly.
Right.
ANDY CONNOLLY: So that makes sense.
So down there are your stem cells, and it grows like that.
So this is a hyperplasia.
So I'd like to show you next the next step, which
is a pre-cancer legion.
Should we do that in another videos?
SAL KHAN: Yeah.
Let's do that in another video.