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- Most cells in the human body just go about their
- business on a daily basis in a fairly respectable way.
- Let's say that I have some cell here.
- This could be maybe a skin cell or really any cell in
- any tissue in the body.
- As that tissue is growing or it's replacing dead cells
- the cells will experience mitosis
- and replicate themselves
- make perfect copies of each other.
- And then those two maybe will experience mitosis
- and then if they realize that, gee, you know
- it's getting a little bit crowded.
- There are other cells in my neighborhood.
- They'll recognize that, and say, you know, I'm going to
- stop growing a little bit.
- That's called contact inhibition.
- And so they'll just start growing.
- And then let's say
- one of them experiences a little defect,
- and he says, you know what, gee,
- something's a little bit wrong with me.
- I, the cell, recognize this in myself, and the cells will
- actually kill themselves.
- That's how good of cellular citizens they are.
- They'll kind of make way for other healthy cells.
- So this guy might even kill himself if he realizes that
- there's something wrong with him.
- There's actually a cellular mechanism that does that
- called apoptosis.
- And I want to make this very clear.
- This isn't some type of outside influence on the cell.
- The cell itself recognizes that it's somehow damaged
- and it just destroys itself, so apoptosis.
- So that's the regular circumstance even when there
- is a mutation.
- And just to give you an idea, even if mutations are
- relatively infrequent.
- And I don't know the exact frequencies at
- which mutations occur.
- I suspect it's of different frequencies in different types
- of tissues.
- There are on the order of 100 billion.
- Let me do it in a different color.
- There are on the order of 100 billion
- new cells in the human body per day.
- So even if a mutation only occurs one in a million times,
- you're still dealing with roughly 100,000 mutations, and
- maybe most of the mutations, maybe they're just some little
- random things that don't really do a lot.
- But if the mutations are a little bit more severe, the
- cell will recognize it and destroy itself.
- And I want to make a very clear point here.
- I'm talking about the cells of the body or most of the body.
- These could be cells in my eyes
- or the cells in my brain or the cells on my leg.
- These aren't my germ cells.
- So these mutations, even if the cell survives
- will not be passed on to my offspring.
- That's an entirely different discussion when
- we talk about meiosis.
- These are all my body cells and they're replicating, and
- we've gone over this with mitosis.
- So any mutations here, they'll either do nothing, or the
- cells might malfunction a little bit, or the cells might
- hurt themselves or hurt me, but they're not going to
- affect my offspring.
- And I want to make that point very clear.
- Now, you're saying, hey, Sal, 100 billion new cells a day?
- That must mean like every cell in my body has created, well
- that just gives you an idea of how many cells we have. We
- actually have on the order of, and you know it's obviously
- not an exact number, but actually in the human body,
- there's on the order of 100 trillion cells.
- And if you look at it that way, you say on average, one
- thousandth of your cells replicate each day, but the
- reality is some cells don't replicate that frequently at
- all and some cells replicate much more frequently.
- Just to take a little side note here, this gives you an
- appreciation, I think, for the complexity of the human body.
- I mean we think of our own world economy and world
- society as so complex, it's made up of 6 billion humans.
- We're made up of 100 trillion cells.
- Let me rewrite 100 trillion in billions.
- 100 trillion can be rewritten as 100,000 billion cells.
- And each one of those 100,000 billion cells are these huge--
- I know I shouldn't use the word huge-- but they're these
- complex ecosystems in and of
- themselves with their nucleuses.
- And we'll talk about all the different organelles they
- have, and we talked about cellular replication, DNA
- replication and how the cell replicates.
- So these things aren't jokes and they have all of these
- complex membranes that take things into them.
- They are creatures to themselves, but they live in
- this complex environment or society that is each of us.
- So that's just a side note just to appreciate how large
- and how complex we are.
- But you can imagine, and this is how I got off on this
- tangent, if we're making on the order of 100 billion new
- cells every day, you're going to have a lot of mutations,
- and maybe some of the mutations, you know I said
- some of them don't do anything.
- Some of them, the cell recognizes that the cell is
- just going to be kind of dead weight so the cell kind of
- eliminates itself.
- But every now and then, you have mutations where the cell
- doesn't eliminate itself and it also deforms the cell.
- So when you have that, let's say I have some cell here.
- I have some cell and it's got some mutation.
- I'll do that mutation with a little x right here.
- That's in its DNA.
- Maybe it's got a couple of mutations.
- So one of the mutations keeps it from experiencing
- apoptosis, or destroying itself, and maybe one of the
- mutations makes it replicate a little bit
- faster than its neighbors.
- So this cell, through mitosis, it makes a bunch of copies of
- itself or a ton of copies of itself.
- And this kind of body of cells that essentially has a defect,
- they're all from one original cell that kept duplicating and
- then those duplicating, but all these are defective cells.
- If you were to look at them compared to the tissue around
- it, it would look abnormal in some way.
- Maybe it wouldn't function properly.
- This is called a neoplasm.
- Now, a lot of neoplasms, well they don't have to
- form a body like this.
- Sometimes they might somehow circulate in the body, but
- most of the time they form this kind of big lump.
- And if they get large enough, they're noticeable.
- And that's when we call it a tumor.
- So if this is actually a lump of kind of differentiated
- tissue that's definitely abnormal, that's
- what you call a tumor.
- So the term neoplasm and tumor are often used
- interchangeably.
- Tumor is the word we use more in our everyday vocabulary.
- Now, if this lump just kind of grows to a certain size, it's
- just there, it doesn't really do anything dangerous, it's
- not replicating out of control.
- I guess it's not replicating a lot faster than its
- neighboring cells and it's just hanging out, maybe
- growing a little bit, but not in any significant way harming
- our environment, we call that a benign
- tumor or a benign neoplasm.
- And benign essentially means harmless.
- Benign tumor.
- That means that's good.
- You want to hear that.
- If you got a lump-- God forbid you have a lump either way--
- but if you do and it's a benign tumor, that means that
- lump, it can kind of stick around, no damage done.
- But if these DNA mutations, and maybe some of these are,
- it is benign, but maybe one of the benign ones has another
- mutation in it that starts making it grow like crazy.
- And not only does it grow like crazy,
- but it becomes invasive.
- And invasive means that it doesn't care what's
- going on around it.
- It just wants to infiltrate everything.
- So let's say that guy grows like crazy.
- Let me do it in a different color.
- And he starts infiltrating other
- tissue, so he's invasive.
- So super growth, he's invasive.
- So he doesn't care what's going on.
- He's all of a sudden turned into some type of a cellular
- psychopath.
- And even worse, his descendants, it's not just one
- cell anymore.
- He just keeps duplicating and passing on this kind of broken
- genetic information that makes it want to replicate.
- And then maybe there could be more and more things that
- break down in its I guess offspring or the DNA that
- comes from its replications.
- And actually, that's a good likelihood, because the same
- parts of its DNA that broke down, some of the DNA that
- broke down in this guy, some of the mutations might have
- actually hurt the DNA replication scheme, so that
- mutations become more frequent.
- So more frequent mutations.
- So as these replicate, more and more mutations appear, and
- then maybe eventually one of the mutations appears that
- allows these cells to break off and then travel to other
- parts of the body.
- And then those parts of the body start to take over and
- start taking over all of the cells.
- And this process is called the cell has-- this is one of the
- hardest words for me to say, something wrong with my
- brain-- but the cell has metastasized.
- You might have heard the word metastasis, and that's just
- the notion of these run amok cells all of a sudden being
- able to travel to different parts of the body.
- And I think you guys know what we call these cells.
- These cells that aren't respecting their cellular
- neighborhood.
- They're growing like crazy.
- They don't experience that contact inhibition.
- They're invasive.
- They start crowding out other cells and
- hogging up the resources.
- And they keep mutating really fast because they have all of
- these genetic abnormalities.
- And eventually they might even break away and start
- infiltrating other parts of the body.
- These are cancers or cancer cells.
- And so you might have an appreciation for
- why this is so hard.
- Cancer is such a hard disease to quote, unquote, cure.
- Because it really isn't just one disease.
- It's not like one type of bacteria or one type of virus
- that you can pinpoint and say let's attack this.
- Cancer is a whole class of mutations where the cells
- start exhibiting this fast invasive growth and this
- metastasis.
- So you might look at one type of cancer and be able to say,
- hey, let's target the mutation where the cells look like this
- and you're able to knock out some of them.
- Let me do this in this color.
- So maybe you're able to knock out that guy,
- that guy, that guy.
- But because their DNA replication system might be
- broken in some way, they continue to mutate, so
- eventually you have one version that's able to not be
- knocked out by whatever method you get.
- And so you have this kind of new form of cancer, and then
- that new form of cancer is even harder to kill.
- So you can imagine that cancer is kind of a
- never ending fight.
- And you kind of have to attack the general idea behind it.
- Chemotherapy and radiation, all of these type of things.
- They try to attack things that are fast growing because
- that's the kind of one common theme
- behind all of the cancers.
- And we could do a whole playlist on what cancer is and
- how people are attacking it, but I wanted to at least show
- you in this video that cancer really is just a byproduct of
- broken mitosis, or even more specifically, broken DNA
- replication.
- That we have all of these cells replicating themselves
- every day on the order of 100 billion, and every now and
- then something breaks.
- Usually when they break, either nothing happens or the
- cell kills itself.
- But every now and then, the cells start replicating even
- though they're broken.
- And sometimes they start replicating like crazy.
- If they just replicate, but they're really not doing any
- harm, it's benign.
- But if they start replicating like crazy, taking over
- resources and spreading through the body, you're
- dealing with a cancer.
- So hopefully, you found that interesting.
- You already know a good bit of the science that kind of deals
- with what is probably one of the worst ailments that we
- deal with as creatures.
- I mean, obviously, we're not the only people who can
- experience cancers.
- Even plants have cancers.