Hematopoiesis | Hematologic System Diseases | NCLEX-RN | Khan Academy

Summary

This educational script explores the fascinating process of hematopoiesis, the formation of blood cells within the bone marrow. It begins by illustrating the components of blood, including red blood cells, platelets, and white blood cells, and then delves into their origin from hematopoietic stem cells. The script differentiates between myeloid and lymphoid lineages, detailing the unique characteristics of T and B lymphocytes, erythrocytes, megakaryocytes, and various types of white blood cells like monocytes, neutrophils, basophils, and eosinophils. It concludes with the developmental stages of these cells, from blasts to cytes, offering a comprehensive yet concise overview of blood cell production.

Takeaways

• 🩸 Blood vessels contain various cells such as red blood cells, platelets, and white blood cells, but are not the site of their production.
• 🦴 Blood cells are produced in the bone marrow, which is a red spongy tissue found in the central cavity of bones.
• 🌱 Hematopoiesis, the process of blood cell formation, originates from hematopoietic stem cells within the bone marrow.
• 🔬 Hematopoietic stem cells differentiate into two main cell lineages: myeloid and lymphoid groups.
• 🛡️ Lymphoid cells include T cells (T-lymphocytes) and B cells (B-lymphocytes), which are key components of the immune system.
• 🔴 Red blood cells, or erythrocytes, lack nuclei and have a biconcave disc shape, appearing paler in the center compared to the edges.
• 💔 Megakaryocytes are large cells that produce platelets through the release of cytoplasmic fragments.
• 🛑 White blood cells of the myeloid group include monocytes, which are known for engulfing bacteria through a process called phagocytosis.
• 🔬 Neutrophils have a multi-segmented nucleus and are a primary component of pus, playing a crucial role in the body's defense against infections.
• 🔵 Basophils are characterized by their blue granules and are involved in immune responses, particularly in allergies.
• 🔴 Eosinophils contain red granules and are involved in combating parasitic infections and modulating inflammation.
• 📚 Immature blood cells are referred to as 'blasts' and mature forms are termed 'cyte', with the exception of neutrophils, basophils, and eosinophils, which develop from a myeloblast.

Q & A

Where are blood cells made?

Blood cells are made inside the bone marrow, which is located in the central cavity of bones.

What is hematopoiesis?

Hematopoiesis is the process of forming blood cells. 'Hemato' means blood, and 'poiesis' means to form or make.

What is the origin cell for all blood cells?

The origin cell for all blood cells is called a hematopoietic stem cell.

What are the two main cell lineages that hematopoietic stem cells give rise to?

Hematopoietic stem cells give rise to two main cell lineages: the myeloid group and the lymphoid group.

What are the two types of lymphoid cells?

The two types of lymphoid cells are T-lymphocytes (T cells) and B-lymphocytes (B cells).

What are erythrocytes and what is unique about their appearance?

Erythrocytes are red blood cells. They have a biconcave shape, making the center of the cell much lighter than the edges due to the concentration of hemoglobin.

What are megakaryocytes and what do they produce?

Megakaryocytes are large cells in the bone marrow that produce small cell fragments called platelets.

Describe the function of monocytes.

Monocytes are white blood cells that protect against bacteria and viruses by engulfing and digesting them, a process known as phagocytosis.

What is a unique feature of neutrophils?

Neutrophils have a multi-segmented nucleus, which is a distinguishing feature.

How can basophils be identified?

Basophils can be identified by their bright blue granules in the cell cytoplasm.

What makes eosinophils distinct?

Eosinophils are distinct due to their bright red granules in the cell cytoplasm.

What are the immature forms of blood cells called?

The immature forms of blood cells are called blasts.

What happens to blasts as they mature?

As blasts mature, they become cytes, which are the mature forms of the cells.

Which cell do neutrophils, basophils, and eosinophils develop from?

Neutrophils, basophils, and eosinophils all develop from a myeloblast.

Outlines

00:00

🩸 Blood Cells and Hematopoiesis

This paragraph introduces the process of drawing blood vessels and the various cells found within them, including red blood cells, platelets, and white blood cells. It explains that these cells are not produced in the blood vessels but are instead made in the bone marrow, a spongy tissue inside the bones. The concept of hematopoiesis is introduced, which is the formation or making of blood, derived from a hematopoietic stem cell. This stem cell is the origin of all blood cells and gives rise to two main cell lineages: the myeloid and lymphoid groups. The lymphoid group is further detailed, describing T cells (T-lymphocytes) and B cells (B-lymphocytes), both of which have large nuclei taking up most of the cell volume.

05:03

🔬 Myeloid Cells and Their Development

The second paragraph delves into the myeloid group of cells, which includes red blood cells (erythrocytes), megakaryocytes, monocytes, neutrophils, basophils, and eosinophils. Red blood cells are highlighted for their lack of a nucleus and their biconcave shape, which resembles a dumbbell. Megakaryocytes are unique for giving rise to platelets through cytoplasmic fragments. Monocytes are characterized by their kidney bean-shaped nucleus and their role in engulfing bacteria. Neutrophils are recognized for their multi-segmented nucleus and presence in pus. Basophils are distinguished by their blue granules in the cytoplasm, likened to a blueberry muffin, while eosinophils are noted for their red granules. The paragraph concludes by explaining the developmental stages of these cells, starting from blasts to cytes, with a special note on the development of neutrophils, basophils, and eosinophils from a myeloblast.

Keywords

💡Blood vessel

Blood vessels are tubular structures that carry blood throughout the body. In the video, the presenter begins by drawing a blood vessel to illustrate the cells present in the blood, such as red blood cells, platelets, and white blood cells.

💡Bone marrow

Bone marrow is the red spongy tissue inside bones where blood cells are produced. The video explains that although blood cells are found in the blood, they are actually made in the bone marrow, highlighting its crucial role in hematopoiesis.

💡Hematopoiesis

Hematopoiesis is the process of forming new blood cells. The term comes from Greek, with 'hemato' meaning blood and 'poiesis' meaning to make. The video describes how all blood cells originate from hematopoietic stem cells in the bone marrow.

💡Hematopoietic stem cell

A hematopoietic stem cell is a stem cell that gives rise to all the different blood cells. The video details how these stem cells differentiate into two main cell lineages: the myeloid group and the lymphoid group.

💡Myeloid group

The myeloid group includes various types of blood cells such as red blood cells, platelets, and some white blood cells. The video contrasts the myeloid group with the lymphoid group, explaining that each type of blood cell falls into one of these categories.

💡Lymphoid group

The lymphoid group consists of blood cells like T cells and B cells. The video describes the characteristics of these cells, emphasizing their role in the immune system and their origin from hematopoietic stem cells.

💡T-lymphocyte

T-lymphocytes, or T cells, are a type of lymphoid cell with a nucleus that takes up most of the cell. The video explains that T cells are crucial for the immune response and are often referred to as 'naked nuclei' due to their large nucleus.

💡B-lymphocyte

B-lymphocytes, or B cells, are another type of lymphoid cell with a large nucleus. Similar to T cells, they play a vital role in the immune system. The video highlights their appearance and function in the body's defense mechanisms.

💡Erythrocyte

Erythrocytes, or red blood cells, are responsible for carrying oxygen throughout the body. The video discusses their distinctive shape and how their hemoglobin content gives them their red color, illustrating their importance in oxygen transport.

💡Megakaryocyte

A megakaryocyte is a large bone marrow cell that produces platelets. The video describes how megakaryocytes release fragments of their cytoplasm to form platelets, which are crucial for blood clotting.

💡Platelet

Platelets are small cell fragments derived from megakaryocytes that play a key role in blood clotting. The video explains their formation and function, emphasizing their importance in preventing excessive bleeding.

💡Monocyte

Monocytes are a type of white blood cell known for their kidney bean-shaped nucleus. The video illustrates their role in engulfing and destroying bacteria, highlighting their function in the immune response.

💡Neutrophil

Neutrophils are white blood cells with a multi-segmented nucleus. The video mentions that they are the main component of pus and are crucial in fighting infections by engulfing pathogens.

💡Basophil

Basophils are white blood cells characterized by bright blue granules in their cytoplasm. The video compares them to blueberry muffins and describes their role in immune responses, particularly in allergic reactions.

💡Eosinophil

Eosinophils are white blood cells with bright red granules in their cytoplasm. The video explains their function in combating parasitic infections and their unique appearance, which distinguishes them from other white blood cells.

💡Blasts

Blasts are the immature forms of blood cells. The video describes how these cells develop into their mature forms, known as 'cytes,' emphasizing the stages of development in hematopoiesis.

💡Cytes

Cytes are the mature forms of blood cells that develop from blasts. The video explains the general pattern of blood cell maturation, using terms like erythrocyte and lymphocyte to illustrate the end stages of cell development.

Highlights

Drawing of blood vessel including red blood cells, platelets, and white blood cells.

Blood cells are not made in the blood but inside the bone marrow.

Bone marrow is the site of hematopoiesis, the process of forming blood.

Hematopoietic stem cells give rise to all different blood cells.

Blood cells differentiate into myeloid and lymphoid groups.

T cells and B cells are types of lymphoid cells, often referred to as naked nucleus cells due to their large nuclei.

Erythrocytes, or red blood cells, are characterized by their lighter center compared to their edges.

Megakaryocytes give rise to platelets through cytoplasmic blebbing.

Monocytes have kidney bean-shaped nuclei and engulf bacteria by surrounding them.

Neutrophils have a multi-segmented nucleus and are the main component of pus.

Basophils contain bright blue granules in their cytoplasm, resembling blueberry muffins.

Eosinophils have bright red granules and sometimes a nucleus in two pieces.

Immature blood cells are called blasts, and mature cells are called cytes.

Neutrophils, basophils, and eosinophils all develop from the same precursor cell, a myeloblast.

Discussion on hematopoiesis ends with the differentiation process from blasts to cytes.

Transcripts

Voiceover: I'm gonna start by drawing a blood vessel.

Inside the blood vessel I'm gonna draw in

some of the cells that you'd expect to see in normal blood.

I'm gonna put in a few red blood cells.

I'm gonna draw in a couple of platelets

which are just fragments of cells

and then I'm gonna put in a few white blood cells.

Even though all of these cells are found in the blood

they're actually not made there.

The cells in the blood are made inside the bone.

If you were to take a cross section of bone,

if you were to take a slice like this

and you looked at it,

you'd see that on the inside of bone

there's a central cavity.

This is the outside part of the bone.

The hard part and this is the central cavity.

Inside that cavity there's this red spongy tissue.

That stuff is called bone marrow.

Bone marrow.

Bone marrow is where all of these blood cells are made.

It's the site of hematopoiesis.

Hemato means blood

and poiesis means to form or to make.

Hematopoiesis is just a scary Greek word

that means to make blood.

Let's take a look at what goes on inside the bone marrow.

What's interesting is that

as different as all of the blood cells are

they all actually originate from the same cell

and that cell is called a hematopoietic stem cell.

This stem cells gives rise

to all of the different cells that you see in the blood.

It gives rise first to two different cell lineages

or two different cell groups.

First there is the myeloid group.

Myeloid group.

which is different from the lymphoid group.

The lymphoid group.

All of the cells that you see in the blood

belong to either the myeloid group

or the lymphoid group.

The lymphoid group includes

two different types of blood cells.

First there is the T cell

or actually that's too big

because this is a very little cell.

That seems about right.

There's a T cell and the majority of the cell

is taken up by the cell's nucleus,

and that's what I'm shading in over here.

So much so that this cell has a nickname.

It's often referred to as a naked nucleus

because it looks like the nucleus

isn't surrounded by very much cytoplasm.

This is a T cell or a T-lymphocyte.

T-lymphocyte.

It's very similar in appearance

to the other type of lymphoid cell.

This cell also has a nucleus

that takes up the majority of the cell

and this cell is a B cell or a B-lymphocyte.

B-lymphocyte, lymphocyte.

Those are the two different types of lymphoid cells.

What about the different types of myeloid cells.

For starters we have a red blood cell.

I guess we should draw that in red.

This is also very small cell.

I'm gonna shade in this cell

so that I can show you that the center of this cell

is much lighter than the edges

or the periphery of the cell.

This is not the cell's nucleus, guys

because we know that red blood cells

don't have nuclei.

What I'm trying to show is that the center of the cell

is much lighter than the periphery of the cell.

I guess I could do a better job of that

if I showed you what this cell looks like on its side.

This is what a red blood cell looks like

when it's laid on its side.

It kind of looks like a dumbbell

where the edges are much thicker

or much wider than the center.

The edges would since they're thicker

they would be much more densely packed with hemoglobin.

Since we know that hemoglobin

is what gives red blood cells their red color,

the edges would then be darker than the center.

Since the center is much thinner

it would have a lot less hemoglobin.

It would be a lot paler in comparison.

We said that this is a red blood cell

but since in science

we never use a plain and ordinary name of things

we call this an erythrocyte.

Erythrocyte which is just a fancy name

for a plain old red blood cell.

What are some of the other types of myeloid cells?

We have this one cell that I'm drawing in over here.

You might say well, that looks nothing like a cell

and you'd be totally right.

This is a very odd-looking, very large cell

and it's called a megakaryocyte.

Even if you never heard of a megakaryocyte before

you may have heard of what it gives rise to

because a megakaryocyte gives off

little blebs of its cytoplasm

to form this small cell fragments

and these fragments are known as platelets.

You may have heard of the platelets before.

The rest of the myeloid cells

are actually different types of white blood cells.

For example you have this one type of white blood cell

and the rest of these white blood cells

are about twice the size of a red blood cell

so that looks like it's twice the size

of a red blood cell to me.

This cell is called a monocyte.

It's known for having this nucleus

that's in the shape of a kidney bean.

That kind of looks like a kidney bean to me.

This is a really cool white blood cell

because it protects us from bacteria

and viruses and other invading organisms

just like any other white blood cell does

but it does so in a very interesting way.

Let's say that this was a bacterium

or actually, no I like the color pink

so let's use a color I don't like.

Let's say that this was a bacterium.

The monocyte would defend us against it.

It would attack this bacterium

by engulfing itself around the bacterium.

When it does that it kind of looks like

it's eating the bacteria.

It looks like its eating the bacterium.

That's a very interesting way

of dealing with these invading organisms.

Let's clear out that.

Mono actually refers to the fact that

this cell has a nucleus that's in one piece

and I guess a lot of these cells have nuclei

that are in one piece.

It makes us wonder what types of cells

have nuclei that are not in one piece

and that would bring us to a neutrophil.

This is a neutrophil.

A neutrophil.

It has a nucleus like I'm drawing in

that is broken up into several different pieces or segment.

The segments are still held together

by little pieces of string.

This is called a multi segmented nucleus.

Even if you've never heard of a neutrophil before

I'm sure you've seen them before

and how do I know that?

It's because neutrophils

are actually the main component of pus.

If you like anybody else has ever popped a pimple

you've looked at a bunch of neutrophils.

What are the other types of myeloid cells?

Well, we have this one cell that's called a basophil.

Basophil.

It looks something like this.

You might say, well, that looks

an awful lot like a monocyte

and you'd be completely correct

except this cell has a very unique feature

that the monocyte doesn't have,

and that is that it has these bright blue granules

in its cell's cytoplasm.

That make it stick out.

The way I like to think of a basophil is like

a basophil is like a blueberry muffin

and that reminds that it has these

bright blue granules in its cell's cytoplasm.

For the last type of myeloid cell we talked about.

Whoops.

For the last type of myeloid cell that we talked about

is an eosinophil.

It's an eosin-O-P-H, P-H-I-L, eosinophil, okay?

It has a nucleus that can sometimes be found

in two pieces.

This is the first piece and this is the second piece

but that's not what makes it so unique.

What it's really well known for

is the fact that it has these bright,

beautiful red granules in its cell cytoplasm.

Those are all of the different blood cells

with all the lymphoid cells on this side

and all the myeloid cells on this side.

It turns out that all of these cells

don't directly develop from hematopoietic stem cell.

Instead they undergo multiple stages of development

to mature into their adult form,

but don't worry guys we're not gonna hash out

each of those different forms and their names

and physical characteristics.

Instead we're gonna make a very general statement.

I guess we could put that up here.

We're gonna say that the immature forms.

the immature forms of all these cells

are called blasts.

When the blast mature, they mature

they are called cytes.

Let me show you what I mean.

To spare you guys the agony

of having to watch me draw out

all of those different forms

I just pasted them in here.

We can see here that what we said about

the immature forms being called blasts

and the more mature form being called cytes is true.

The T-lymphocyte develops from a T lymphoblast

just like an erythrocyte develops

from an erythroblast

and a megakaryocyte develops from a megakaryoblast.

You guys get the pattern.

The only wrench I'm gonna throw into this pattern

is with the neutrophil, basophil and eosinophil

which all actually develop from the same cell

and that cell is called a myeloblast.

I think that that's a reasonable place

to end our discussion on hematopoiesis.