Hi. It's Mr. Andersen and welcome to biology essentials video 37. This is on
cell communication. In other words how cells communicate with other cells. And what I thought
I'd do is start with some analogies. I want to show you how I communicate with other people.
And how those communications are similar to the communications that we see in cells. So
let's first of all start with the post-it note. Post-it note works great if you want
to take a message and hand it specifically to someone else. And so for example, let's
say I have a grocery list. I write down the things that we need at home, I hand it to
my son and I say please get these things at the store. He can always check on the list
to make sure it's matching up with the things that we actually require. And so it works
great. But you have to hand it off from one person to another. Next is the e-mail. And
so Gmail works great for me. If I want to send a message to a student, a specific student,
then I send an e-mail. Works great because I can send it to a specific student. I don't
have to physically be next to that person to send it to them. And then the last one
would be Facebook. Like a, I don't do many status updates, but if I were to post this,
"Working on a communication podcast by myself. Ironic." A Facebook status post is not going
to one person, it's going to all of my friends and so then they can determine if they want
to like it or dislike it or ignore it or unfriend me as a result of that. And so those are three
ways that I communicate with people. And that is really similar to the way cells communicate.
And so the first one is when there's no distance between cells. In other words you have to
make sure a message gets from one cell to another, then we can use cell to cell contact.
And so an example I'll talk about in this is the antigen presenting cell. And so that's
when one cell is sending a message to another. Also like plant cells for example have these
little holes called plasmodesmata and they can actually send messages from cell to cell.
Next one I'll talk about are local regulators. If it's a distance that's short and I want
to make sure that it goes to one other cell, cell to cell, I could use something called
a local regulator. And so an example I'll talk about is when you have a neuron connected
to another neuron through a synapse. You can send a neurotransmitter to make sure that
message gets across. Again it's going just from one cell to another. Let's say it's a
distance that's long or an audience that's large, you want to send that information,
we could use something like a hormone. And so the one I'll talk about is human growth
hormone. And nice thing about that is you can send it from not only just one cell or
excuse not just to one cell, you can send it to multiple cells. And then they can figure
out based on that message if they really want to act on it or not. And that's why it's a
lot like a status post. And so let's first of all start with a contact, in other words
specific contact between two cells. And the example I'm using here is the immune response.
And so an antigen is an invader. So it could be for example a bacteria or a virus. And
so we have cells called antigen presenting cells. An example would be a macrophage. And
it can actually sense the shape and then pass that off to make antibodies, more macrophages
and then killer T cells. And so what sits in the center of this whole thing is the T
helper cell. And it has to know specifically what the shape is. And so let me show you,
I've made a little animation that explains this. This is like the post-it note. And so
let's say we have our antigens. So we have our virus. And this would be our macrophage.
And so what it's going to do is it's going to grab on to that antigen. And it's going
to envelope it. It'll put it inside this little phagocyte or this little phagosome which is
a little bubble. It'll then have a lysosome come next to it that will spill some digestive
enzymes into it and it'll chop up it up into a million little pieces. Next it will let
that go, but you'll notice as it moves out that it's actually, part of it is being carried
to the surface. The shape of a part of that antigen is carried to the surface. And now
we have our helper T cell. And so the helper T cell is going to pass off, let me get a
marker, it's going to pass that shape to the helper T cell. And so that protein that was
inside the macrophage is called the MHC2. It's a protein, major histocompatability complex
2. It's just a protein that brings the surface of that antigen to its surface. It's then
going to link up with a CD4, which is another protein on the surface of the helper T cell.
So let me get all of this scribbling out of the way. So there will actually be a connection
between those two cells. And what it's really sending is this shape of that antigen to that
helper T cell. Okay. Now it's activated the helper T cell. It know the shape of that antigen
so the macrophage isn't required anymore. It's going to go eat some more of those antigens.
And now that helper T cell can send that message to a B cell. So it can make plasma cells.
Make more antibodies. It could also make more memory cells. It's also going to activate
a killer T cell. And a killer T cell now knows that shape as well. And it's going to target
any cell inside our body that's actually infected with that. And so by passing that message
off just like a post it note, we're sure what that shape is. Next one is the idea of a local
regulator. Now there's a distance between those two cells but we still have to make
sure that message gets across. A perfect example of this would be when neurons are connected.
And so a neuron is going to take a message. So let's say I poke my finger right here.
It's going to send that message eventually to my spinal cord, eventually to my brain
and then back again so it can act on that. And so that message is going to travel in
this direction. And it's eventually going to hit another neuron. And so it's eventually
going to have to travel over here. But what's interesting is right here where those two
neurons come together, they're not actually connected. Now we still want to make sure
that message gets across. Because we want to make sure that message keeps going all
the way down here to the brain. But they're not connected. And so we have to use a local
regulator to make sure that message gets across. An example would be a neurotransmitter. And
so that message is coming down neuron A. It's going to move down neuron B. But the way it
works is that we're actually going to release chemicals. Those are called neurotransmitters.
They'll move across that synapse or across that gap. They're going to open up some other
channels. Which is eventually going to get an influx of ions and it's eventually going
to send that message on it's way. And so these right here, neurotransmitters, are chemicals.
And those chemical signals are going to float right across that gap. Now they're not really
going to float out to another neuron. They're quickly going to breakdown. And so it's just
like an e-mail. It's a message going from this cell to this cell. Now you might think
if you're smart, you might think what's the point of that? In other words, wouldn't it
be smarter to just have those two neurons connected together so the message is going
to go across quicker? That's a really good question. And what we think, scientists think,
is that by opening it up, by allowing theses local regulators to go across, it gives us
control over how much of that signal gets through. If it gets through. If we can block
this signal so it doesn't get across. And so we think that our brains have gotten bigger
and bigger and bigger by adding more neurons, but probably what's more important than adding
more neurons is adding these connections between neurons. Let me give you an example of this.
I'm a distance runner and so I love these beta endorphins. Endorphins are natural opiates
made by your body. Now what they do is they block pain. And so if you go for a run, here's
Paula Radcliffe, she's a marathon runner, if you go for a run and you're out there for
10 minutes, you won't feel these. Or 40 minutes, you won't feel these. But a couple of hours
in, if you're out there for two hours, if you could make it that long, you're body is
going to start secreting these beta endorphins. And those are neurotransmitters. They'll move
into nerves in your central nervous system. What they'll do is they'll block pain. And
so even though the signal is actually a pain is traveling into your brain from your body.
It really hurts to run that far, you're actually breaking it, that connection. And that shows
you how it's important to have control over that synapse. Now humans have created things
that mirror this. And so heroin or morphine, they really resemble the structure of endorphins
because they're going to trigger those same responses inside our brain. Last thing I want
to talk about is that Facebook status post. When you want to send a message and it's going
to go to everybody. And they're going to figure out how to act on that. An example I'll talk
about would be, I mean this is a hormone that we're now talking about. A hormone is simply
going to be a chemical. And that chemical is going to spread throughout your whole body.
And so an example of one would be the growth hormone. Growth hormone is especially going
to be secreted by the pituitary as a human goes through puberty. And so as your body
gets larger and larger and larger, the way that works is we secrete a growth hormone.
The cells are going to pick it up. So for example muscles will grow. Bones will grow.
And here's actually a list of all the things that will happen as we increase the amount
of growth hormone. So for example all of the organs will grow but the brain won't grow.
And we'll get glucogenesis in the liver. Or uptake of glucose. Or stimulates the immune
response. In other words, all of these cells in your body are receiving that same message
from human growth hormone. But they're acting on that. And so that's like that status post.
It goes to everybody, but you can choose to like it or ignore it or act as a result of
that. Sometimes the message will go out of control. And so this is Robert Wadlow. Robert
Wadlow is a pituitary giant. And the reason he was a pituitary giant we now know is that
he had a tumor that was pushing on his pituitary gland. As a result of that he created more
human growth hormone. And more human growth hormone and more human growth hormone and
you can see he was, I don't know, well over 8 feet tall. And so this is just a hormone
and it's acting on all the cells in your body. And so when the distance is large and you
want to touch a lot of different cells, you're going to use something like a hormone. And
so that's how cells communicate. It's not that different from the way that we communicate.
You just have to know your audience and send a message that's appropriate. So I hope that's
helpful.