0:00:01.826,0:00:05.110
Voiceover: All over our[br]body we have blood vessels

0:00:05.110,0:00:07.115
and in those blood[br]vessels we've talked about

0:00:07.115,0:00:10.610
how we have lots of different[br]kind of blood cells.

0:00:10.610,0:00:14.163
We have some red blood[br]cells that I'm drawing here.

0:00:14.609,0:00:16.297
But if you watched our[br]immune system videos

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you'll also know that we have some T-Cells

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and some B-Cells and some macrophages

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and some platelets.

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And all in all actually there's[br]pretty much 10 different

0:00:32.450,0:00:36.829
kinds of blood cells that we[br]have in our blood at all times.

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In this video I'd like to[br]talk a little bit about where

0:00:39.114,0:00:42.162
they're made, which[br]you might already know.

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And also from what precursor[br]cells they're made,

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because cells don't[br]just come out of nowhere

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they come from precursor cells that divide

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and produce new ones.

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So do you know where all[br]these cells come from?

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Where they're made?

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I'm going to draw the[br]answer cartoonish as always

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and not to scale with this blood vessel.

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So here's a bone and the answer is that

0:01:01.994,0:01:04.532
all these cells come from the bone marrow,

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which is inside the bone here.

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Voiceover: Now when I[br]first heard this I thought

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to myself, "How is it[br]possible that blood cells come

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"from inside the bone,[br]get through the surface

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"of the bone and get into blood vessels?"

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Well you might be[br]surprised to know that all

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these bones are actually[br]profuse with blood vessels

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themselves, they're very[br]small and difficult to see.

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So it's actually quite[br]easy for cells to hop into

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these blood vessels and[br]go into blood vessels

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of the body.

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But now let's talk about[br]those precursor cells.

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So it turns out and this is something

0:01:36.139,0:01:37.938
that we didn't know for a long time.

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But it turns out that there's[br]one powerful stem cell

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in your bone morrow that[br]can make all 10 kinds

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of blood cells and that one[br]cell, that very powerful cell,

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has a bit of a complicated name[br]which we'll write out here.

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It's called a pluripotent ...

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Pluripotent if you're good[br]with your latin you know

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that this means, I guess,[br]"Able to do a lot of things."

0:02:02.462,0:02:04.755
That might be a poor[br]translation but anyway.

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Pluripotent hematopoietic[br]because hematopoiesis

0:02:09.231,0:02:16.556
is the process of producing blood cells.

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So that's pluripotent[br]hematopoietic stem cell.

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Because Stem Cells as[br]you may know are cells

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that can divide into multiple[br]different kinds of cells.

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And now I'd like to ask[br]you a question which is,

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do you think that a macrophage which,

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if you watched the[br]immunology video as you know,

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is a big phagocytic cell[br]so it's like to swallow

0:02:40.596,0:02:43.556
invaders or debris, do you[br]think that the macrophage

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is more closely related to a B-Cell which

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as you know produces[br]anti-bodies or a red-blood cell?

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You might be surprised by the answer.

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The answer is actually[br]macrophage is more closely

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related to the red blood[br]cell, which is kind of weird

0:02:59.115,0:03:03.069
because macrophages and[br]B-Cells are both immune cells.

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And red blood cells are not.

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This pluripotent hematopoietic[br]stem cell gives rise

0:03:08.348,0:03:11.732
to two main lineages[br]and I'll draw them here.

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The first is the myeloid lineage ...

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And the other is the lymphoid lineage.

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So when this pluripotent[br]cell here first divides,

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It can give rise to one[br]of these or one of these.

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And these are also precursor[br]cells to the 10 kinds

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of red blood cells that we[br]actually find in our blood.

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So these are not the ones[br]that are going to end up

0:03:43.693,0:03:46.661
in our blood, these are guys[br]who sit in the bone marrow

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and make the cells that[br]end up in our blood.

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So now it turns out that[br]this lymphoid progenitor cell

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can make actually three[br]different kinds of immune cells

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in our body, it makes an NK cell ...

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It makes a B cell ...

0:04:05.827,0:04:08.481
And it can make a T Cell.

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And this is three out[br]of our ten blood cells

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that we talked about[br]and so the other seven

0:04:22.299,0:04:25.157
are going to be from the myeloid lineage.

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And one of those is, as[br]you could've guessed ...

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The red blood cell.

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Another is the megakaryocyte[br]which you may not

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remember what it does so[br]I'll tell you in a moment

0:04:41.397,0:04:43.370
but try to remember.

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The megakaryocyte is actually[br]what makes platelets.

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So the megakaryocyte[br]buds off little pieces

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of it's cytoplasm surrounded by membrane

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and these are platelets.

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But the myeloid lineage also[br]makes a bunch of immune cells

0:05:04.741,0:05:09.360
in addition to the red blood[br]cells and the platelets.

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And you may not have heard of these,

0:05:12.733,0:05:14.549
so I'll just list them here.

0:05:14.549,0:05:16.925
One of them is the neutrophil, that one

0:05:16.925,0:05:19.009
you're most likely to have heard of

0:05:20.470,0:05:22.224
and there's two other cells

0:05:22.224,0:05:23.749
which are very similar to the neutrophil,

0:05:23.749,0:05:26.688
one is called the basophil ...

0:05:27.657,0:05:30.396
And one is called the eosinophil.

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And don't feel too bad[br]about not having heard

0:05:33.689,0:05:35.176
about these because they're[br]actually pretty rare

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in your blood, they are there,

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but there aren't many of them.

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And then there's also a[br]monocyte which is fairly

0:05:40.949,0:05:45.241
similar to these three[br]above and the monocyte

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is actually what becomes[br]a macrophage later on.

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You're probably familiar with macrophage,

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a monocyte is just a[br]slightly less differentiated

0:05:53.690,0:05:55.865
version of a macrophage.

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And finally, there's also mast cells.

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And mast cells are the ones that ...

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So these are our seven other cells ...

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and as you can see what we[br]said in the very beginning

0:06:16.750,0:06:18.545
is in fact true.

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The red blood cell is more closely related

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to the monocyte or the[br]macrophage than is a B cell

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or a T cell or something like that.

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And now I'm adding an[br]addendum to this video

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to mention one other kind[br]of cell that we've talked

0:06:37.391,0:06:40.231
about in the past videos but[br]that I didn't put on this chart.

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And that kind of cell[br]is the dendritic cell,

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it's one of the antigen[br]presenting cells that we talked

0:06:45.625,0:06:47.729
about and I want to ask you, do you think

0:06:47.729,0:06:50.873
the dendritic cell comes[br]from the myeloid lineage

0:06:50.873,0:06:52.912
or the lymphoid lineage?

0:06:53.297,0:06:54.697
And it's actually a trick question because

0:06:54.697,0:06:57.185
the answer is it comes from both.

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So we have some dendritic[br]cells that I'm drawing here,

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which come from the myeloid lineage.

0:07:02.689,0:07:05.228
And some which I'm[br]drawing right next to it

0:07:05.228,0:07:08.493
which come from the lymphoid lineage.

0:07:08.493,0:07:10.145
And it turns out that[br]the ones that come from

0:07:10.145,0:07:14.524
the myeloid lineage are[br]created from monocytes

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whereas the ones that come[br]from the lymphoid lineage

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are not really descendants[br]of B or T cells,

0:07:20.937,0:07:23.441
they come from some lymphoid precursor.

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So dendritic cells are[br]kind of a weird exception

0:07:25.617,0:07:28.553
they can be made from[br]either line and I wanted to

0:07:28.553,0:07:30.521
add yet another piece[br]of information hopefully

0:07:30.521,0:07:33.105
not overloading this too[br]much just to remind you

0:07:33.105,0:07:35.569
once again that monocytes in addition to

0:07:35.569,0:07:40.137
becoming dendritic cells[br]can also become macrophages.

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And macrophages we are[br]certainly familiar with,

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At least we've talked about[br]them in the other videos.

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So here's a macrophage, and macrophages

0:07:47.561,0:07:49.641
if you remember are[br]kind of like sentinels,

0:07:49.641,0:07:52.984
they sit out in the tissues[br]and watch for invaders

0:07:52.984,0:07:55.697
and dendritic cells also behave like that.

0:07:55.697,0:07:57.178
So what about this monocyte?

0:07:57.178,0:07:58.181
Does he do the same thing?

0:07:58.181,0:08:00.420
Well actually no, it[br]turns out the monocyte

0:08:00.420,0:08:04.145
is kind of like a circulating[br]version of macrophages

0:08:04.145,0:08:05.537
or dendritic cells.

0:08:05.537,0:08:06.841
So what do I mean by circulating?

0:08:06.841,0:08:08.842
I mean that it's actually in the blood.

0:08:08.842,0:08:10.961
So monocytes move around in the blood

0:08:10.961,0:08:13.689
and then when they go into[br]the tissues to settle down

0:08:13.689,0:08:16.385
and become sentinels,[br]that's when they are turned

0:08:16.385,23:59:59.999
into either macrophages[br]or dendritic cells.