An introduction to Haematopoesis

hello in this video we're going to talk

about H poesis hamat poesis as a name

suggests Hamato refers to uh the blood

and poesis is essentially I guess

formation of and hop poesis it refers to

the commitment and differentiation

process of a stem cell to the different

types of cells we found in the blood for

example our red blood

cells now metap poesis which is the

making of these different cells they

occur mainly in the bone marrow and this

is particularly in adults this is

referred to as Moler hematopoesis but

hematopoesis can also occur in other

tissues such as the liver thymus and

spleen and this is called extra

hematopoesis and we'll learn about that

in this video so let's begin by zooming

into the bone marrow and in the bone

marrow we can find hematop potic stem

cells hematopoetic stem cells can first

of all differentiate into either what's

called a common lymphoid progenitor cell

or a common myoid progenitor cell the

common lymphoid progenitor cell then

further differentiates into different

lymphoblasts with different genetic

profiles and this will allow them to

form and mature into different types of

lymphocytes so here I'm just drawing the

bloodstream because as cells exit the

bone marrow they will enter the blood so

these different lymphoblasts they with

the different genetic profiles will uh

will become either naive B cells pre-t

cells or natural killer

cells now also common lymphoid genital

cells can differentiate into certain

types of dendritic cells the dendritic

cells when it's formed will move into

tissues and come and becomes what's

known as lymphoid dendritic cells

dendritic cells are peripheral antigen

presenting cells that are actually very

important in the connection between the

innate immune system and the Adaptive

immune

system so that was the lymphoid

progenitor cell

lineage now let's look at the common

myoid progenitor cell lineage and it's

important to know that the outcome of

these of these lineage are cells that

can circulate in the blood so hence

hematopoetic so again from the from the

hematopoetic stem cell it can become a

common myoid progenitor cell

and there are different maps of of

hematopoesis that depicts common mid

progen progenitor cell differentiation

but how I'm going to show you is what I

think is the easiest anyway the common

myoid progenitor cell can become Milo

blasts and eventually become

granulocytes these granulocytes are

cells containing granules and they can

either be band

neutrophils band basophils and band

eils so neutrophils basophils eils and

these granulocytes are band cells

because they are immature but once they

enter the circulation they mature and

become what we know as neutrophils

basophils and eils

respectively neutrophils are important

in the acute response to infection and

inflammation basophils are important in

allergy and parasitic infections and

eils are also important in allergies and

sensitivity the common myo progenitor

cells can differentiate and become Pro

monocytes and Mast Cell

precursors the

prosites then mature and become what we

know as monocytes monocytes are

essentially circulating macrofagos and

so once they move into a tissue such as

the skin they become tissue

macrofagos and macrofagos are antigen

presenting cells which again are

important in the connection between the

innate immune system and the Adaptive

immune

system the monocytes or Pro monocytes

can also become dendritic cells and if

they become dendritic cells in the

tissue they are referred to as the myoid

dendritic cells

so again we have two important antigen

presenting cells the maccrage and the

dendritic

cell the muscel

precursor um can become mature muscels

once they enter circulation and move

into tissues M cells are very important

cells in allergy the inflammatory

response and hypers

sensitivity finally the common myoid

progenitor cell can different and become

Mega oyes with stimulation of Throop

potin a hormone produced by the liver

and the

kidneys or the myoid progenitor cell can

become erythroblasts through stimulation

of erythropoetin a hormone released by

the

kidneys let's look at Mega Cario sites

first mega Cario sites are normally

present in the bone marrow not in the

circulating blood but these guys give

rise to the platelets we find in the

blood Mega Cario sites rupture releasing

PL platelets into circulation and

platelets are very important in

clotting Arro blasts are still nucleated

red blood cells meaning that they have a

nucleus but once these arthro blasts

enter circulation and mature they become

erthrocytes which are

anucleated erthrocytes are our red blood

cells in adults healthy adults

hematopoesis occurs in the bone marrow

particularly in the pelvis the vertebrae

and sternum however hematopoesis can

occur in other organs and this is called

extra medary homat poesis and let us

look at a graph with being the

timeline here is birth and down the

xaxis to 70 years old and on the Y AIS

is hematopoesis where the blood cells

the different blood cells are made so

before birth so when you are a fetus in

the uterus hematopoesis occurs

predominantly in the liver and the

spleen and this is the fetus we're

talking about so in the fetus

hematopoesis occurs in the liver and

spleen but then it drops off by birth

and this is because slowly the bone

marrow will take over um the role and by

adulthood the bone marrow has the main

role in hematopoesis

parly the vertebrae bone marrow and the

pelvis and

sternum hop poesis occurring in the bone

marrow is termed mol hamop

poesis it's interesting to note that hop

pois also Al occurs in the lymph node

during adulthood but at a much lower

concentration and usually occur uh more

often uh during periods of

infections so what is very interesting

is that the liver and spleen as one

might suspect has no to minimal role in

hematopoesis after birth however they

actually do have a role particularly

during periods of infections or during

pathological changes such as in certain

diseases when other organs perform

hematopoesis asides the bone marrow such

as if it happens in the lymph node

spleen or liver this is called extra

hematopoesis

when you think about it a child with an

infection their liver or spleen can

sometimes enlarge and this is because

the spleen or the liver is working

harder to make more blood

cells but these are but this is usually

self-limiting and goes away