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Course: Health and medicine > Unit 6
Lesson 8: Myeloproliferative disordersWhat are myeloproliferative disorders?
Learn about 4 different cancers that involve the bone marrow and produce a large number of cells in the blood stream. By Raja Narayan.
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Want to join the conversation?
- is chronic myelogenous leukemia different from chronic myeloid leukemia?(2 votes)
- Actually this terminology is used to refere to the same myeloproliferative disorder, The same happens with lymphoblastic/lymphoid leukemia.(3 votes)
- Whats so bad about Polycythemia Vera?(0 votes)
- Too much of a good thing is a bad thing. Physiology is about balance. Here we have a bone marrow stem cell making too many RBCs and in the short term the blood is thicker and more likely to clot. So, the blood pressure rises as the heart works harder to move the blood and thrombi or blood clots can form blocking off oxygen to tissue, causing it to die. Overtime, other types of bone marrow products such as WBCs and platelets can increase as well because the bone marrow stem cells are out of control.(5 votes)
- Do myeloproliferative diseases typically not affect the lymphoid lineage?(1 vote)
- If you have all those extra bone marrow wouldn't that make me super strong?(1 vote)
- No - compact bone is what gives bone its rigidity.(1 vote)
- isn't it wrong to depict all this occurring in the femur seeing it's not really a site of haematopoeisis in adults?(1 vote)
- Depicting all hematopoietic stem cells in the femur is not properly illustrative; however, it is a common representation that is easily drawn opposed to drawing every bone that can possibly produce blood cells.(1 vote)
- Would your physical appearance change if your liver or spleen swells up like that?(1 vote)
- aren't haematopoeitic stell cells multipotent rather than pluripotent (pluripotent meaning the cell can differentiate it any of the 3 germ layers). could anyone shed any light on this? i'm aware that the origins of some blood cells are not all that clear, especially mast cells, for example, but i'm pretty sure they all originate from the mesoderm.(1 vote)
- I have had this same question. Hematopoietic stem cells seem to be interchangeably called multipotent and pluripotent. Someone described it to me as this: Blood stem cells can produce all blood lineage cells therefore it is a Pluripotent Hemopoietic Stem Cell (Multipotent would be just as appropriate). It's not precisely correct but in terms of pluripotency of upstream stem cells but using Pluripotent with Hematopoietic indicates the exact stem cell.(0 votes)
Video transcript
- [Voiceover] So in the
next couple of videos, we're going to talk about myeloproliferative disorders. Myeloproliferative disorders. This group of diseases
involves the bone marrow because that's what myelo means. It's just a term for the bone marrow. And in this group of disorders,
you are proliferating, you are proliferating or you are making too much bone marrow. Now to be clear, there are a lot of things that we make in the bone marrow, so I've drawn a bone right here. This is your standard femur and the marrow is usually
located in the shaft of long bones like the
femur or maybe the humerus or even in your vertebral
bodies in the spinal column. But we'll use this as
an example right here. The bone marrow makes
all of the blood cells in our blood stream, and it all starts from a single precursor that's known as a pluripotent. Pluri meaning almost the
same thing as plural, so many potency in making hematopoietic, hematopoietic, which you might
recognize as the same sound as the term hematology, which is the study of blood, stem cells. So pluripotent hematopoietic
stem cells are cells within the bone marrow
that have the ability to make all different types of blood cells that we find in the blood stream. So I'll draw one of them right here, and let's go through
and make a quick chart of all the different types of
blood cells that we can have. There's one key lineage up there and I'll draw another one down here that's gonna be less important for these disorders we're
about to talk about. Both of these are also stem cells, so I'll code them both in yellow. Up here we're talking about
the myeloid stem cells. This is the myeloid stem cell which is why it's most relevant for
the type of disorders we're about to talk about. Whereas down here we are talking about the lymphoid stem cell. The lymphoid stem cell
that you might recall sounds a lot like lymphocytes and that's sure enough what it produces. The lymphoid stem cell will go on to make three main types
of cells over time, so I'm sort of abbreviating it here. There are many steps in between. And I'll draw them out
in this color right here just to distinguish them
'cause they're not stem cells but they have a different property that I'll mention in a minute. But the lymphocytes or the lymphoid cells that you end up with are your B cells, you get some T cells as well, and in addition you also get
these natural killer cells. And that's all I'll say
about that lineage for now. Up here for the myeloid stem cells, there are four specific types of pathways that we go through, so I'll
draw them out right here. The first type of cell that can branch off a myeloid stem cell is called a proerythroblast. A proerythroblast. And this guy will go through a whole bunch of divisions to eventually
make what's referred to as a, or rather, as an erythrocyte. So this is an erythrocyte that you may more commonly refer to
as a red blood corpuscle, or a red blood cell. Next down here, what we can make off the myeloid stem cell is something that's called a myeloblast. A myeloblast. And the myeloblast itself can divide into three different
types of cells as well. And I'll draw them each right here, but the sizes are not going
to be quite representative. I'm just trying to show
them here schematically. We'll get some basophils, which you may have heard of before, eosinophils. So that's eosinophils. And finally you can also
get some neutrophils. Neutrophils. Another lineage that you
can have dividing off of the myeloid stem cell
is through the monoblast, so a monoblast. And this guy, which you
may be able to guess, will divide into this cell right here, which is known as a monocyte. And for the final lineage, I'm going to draw somewhat
of a bigger cell right here because it's supposed to
accommodate a bigger nucleus. This is a megakaryoblast. A megakaryoblast. Mega meaning big, karyo meaning nucleus. The megakaryoblast will divide
into big megakaryocytes, so I'll write that here, megakaryocyte, and then these then will fragment. It's very unusual. It's not like the other
cells we talk about above, but these cells will
break apart into pieces. So there are six pieces I drew here. So there should be six
pieces that come out on the other side right here. And these aren't perfect but they show that there are six pieces
coming off the megakaryocyte, and each of these pieces
are known as a platelet. So these are your platelets right here. And that's the gist of how you get all the different blood cells off of this single pluripotent
hematopoietic stem cell in the bone marrow. Myeloproliferative disorders
occur when there's a defect, so I'll write that up here. There's a defect in a
receptor tyrosine kinase, which may be something
you've heard of before if you're familiar with enzymes. A defect in a receptor tyrosine kinase that is responsible or
involved in cell division. The activation of this
receptor tyrosine kinase regulates whether cells
are allowed to divide along these various lineages or if not, if they're supposed to pause until it's more appropriate
for them to divide. The mutation that occurs allows this receptor tyrosine
kinase to just always be on, and there are different
points along the way where we can have this receptor
tyrosine kinase turned on. Say if we have the mutation occurring along this path right here. That defect is associated with
a myeloproliferative disorder known as polycythemia, polycythemia vera, where you have poly, meaning a lot of different cells that are produced, and so you'll get a bunch of erythrocytes, basophils, neutrophils, all of these guys, in the blood stream. Or let's say you have
the defect right here, where the myeloblast branches off. In that case, you would have a disorder known as chronic myelogenous, chronic myelogenous leukemia. Chronic myelogenous leukemia. And you might recall leuk meaning white, which refers to leukocytes, which I've colored in all of
these little beige colors here. All of these refer to leukocytes. This defect will produce a
whole bunch of leukocytes and it'll mainly be
these that we see up here through the myeloblast lineage. Or let's say we have a defect in the platelet lineage around here. We can have a disorder
that's known as essential, essential thrombocythemia. Thrombocythemia. And thrombocyte, I should've mentioned this earlier when I was writing out platelets, but thrombocyte means the
same thing as platelets. Or finally you could even have a defect so early on right here,
before you even get to the pluripotent
hematopoietic stem cell. And you have what's referred
to as primary myelofibrosis. Primary myelofibrosis,
which you might recall as meaning fibrosis or
connective tissue being put in the bone marrow, which
is not where it should be. So that would be a big problem for us. And when this occurs, you'll
get an additional defect known as myeloid metaplasia, which means various other
organs in your body, like what I've drawn here is
your liver or your spleen, will start making these
hematopoietic stem cells, causing them to become really big. So your liver might end up
being that big and bulge out, or your spleen could also
become pretty large as well. And in fact, when you have
enlargement of your liver, or what's known as hepatomegaly, or enlargement of your spleen, which is known as splenomegaly, these were things that you can also see with these other disorders
that I've mentioned up here, because now they're kicked into overdrive in producing these types of cells. And not just in these organs
but in other bones of the body like the skull, for instance. You can start having these
hematopoietic stem cells put out these cells at a rate that they're not supposed to be, which can cause the
bones to grow and produce an abnormal appearance
that's very recognizable. Many of these disorders can also go on to produce what are
called acute leukemias. I think we know what
leukemias are already, but acute just refers to
what stage of development these leukocytes will be put
out into the blood stream. And acute leukemias will
happen when you have a defect that occurs before the
leukocytes are put out. So can you guess which
of these four right here would not have an acute
leukemia associated with it? I think you reasoned correctly. If you think about polycythemia vera, we have the defect here and so sure enough we can produce abnormal
amounts of leukocytes. Chronic myelogenous leukemia, that's before leukocytes are produced. Primary myelofibrosis, the defect is here. That's definitely before
leukocytes are produced down here. But with essential thrombocythemia, the defect happens after
your leukocytes branch off. So you will not see acute leukemias occur with essential thrombocythemia. And there are small
nuances sort of like that that we can talk about to
describe the different types of myeloproliferative disorders and how you can differentiate when one occurs versus the other, which we'll talk about in
the next couple of videos.