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Things to learn:-
Hematopoiesis or hemopoiesis
Site of Hemopoiesis
Stages of hemopoiesis,
Regulating factors on hemopoiesis
Hemo: Referring to blood cells Poiesis: “The development or production of” The word Hemopoiesis refers to the production &
development of all the blood cells: ◦ Erythrocytes: Erythropoiesis ◦ Leucocytes: Leucopoiesis ◦ Thrombocytes: Thrombopoiesis.
Begins in the 20th week of life in the fetal liver & spleen, continues in the bone marrow till young adulthood & beyond!
Derived from the extra- embryonic YOLK SAC;
Consists mainly of nucleated erythroid cells that carry oxygen to the developing embryonic tissues… an early circulatory system.
Probably starts 2 weeks of
intrauterine life
As the embryo’s size increases,
primitive system superceded by
definitive hematopoietic system,
which originates in the embryo
itself and continues throughout adult
life.
1st definitive multipotent
hematopoietic stem cells are
generated within the embryonic
AGM region of the para-aortic
splanchnopleuric mesoderm (day 30-
37 in human)
Throughout fetal life, the liver is the chief organ for production of myeloid and erythroid cells
After birth, BONE MARROW becomes main hematopoietic organ.
• Mesoblastic stage-
in the yolk sac
Starts at 2 weeks of intrauterine life
intravascular
• Hepatic stage-
2-7 months
Both liver and spleen
• Occurs in bone marrow
• Starts at 5 months of fetal life and takes over completely at birth
• Red bone marrow of all bones
• Late adult life, red marrow of flat bones
Active Hemopoietic
marrow is found, in
children throughout
the:
◦ Axial skeleton:
Cranium
Ribs.
Sternum
Vertebrae
Pelvis
◦ Appendicular skeleton:
Bones of the Upper &
Lower limbs
In Adults active
hemopoietic marrow is
found only in:
◦ The axial skeleton
◦ The proximal ends of
the appendicular
skeleton.
The bone marrow is actually one of the largest organs in
the body, approaching the size and weight of the liver. It is
also one of the most active.
Normally, 75% of the cells in the marrow belong to the
white blood cell-producing myeloid series and only 25%
are maturing red cells, even though there are over 500
times as many red cells in the circulation as there are white
cells.
This difference in the marrow reflects the fact that the
average life span of white cells is short, whereas that of red
cells is long.
These cells have extensive proliferative capacity and
also the:
◦ Ability to give rise to new stem cells (Self Renewal)
◦ Ability to differentiate into any blood cells lines
(Pluripotency)
They grow and develop in the bone marrow.
The bone marrow & spleen form a supporting
system, called the
“hemopoietic microenvironment”
PLURIPOTENT STEM CELL
STEM CELL
MULTIPLICATION COMMITTMENT
COMMITTED
STEM CELL
COMMITTED
STEM CELL
MULTIPLICATION
PROGENITOR
CELL
CFU: COLONY
FORMING UNIT
Hematopoietic stem cells (HSCs) are bone marrow cells
that are capable of producing all types of blood cells.
They differentiate into one or another type of committed
stem cells (progenitor cells). These in turn form the various
differentiated types of blood cells.
There are separate pools of progenitor cells for
megakaryocytes, lymphocytes, erythrocytes, eosinophils,
and basophils; neutrophils and monocytes arise from a
common precursor.
• Totipotential stem cells- convert into any tissue type
• Pluripotent stem cell- Pluripotent hematopoeitic stem
cell
• Committed stem cells- CFU E, CFU G, CFU M, etc
Committed stem cells lose their capacity for self-
renewal.
They become irreversibly committed.
These cells are termed as “Progenitor cells”
They are regulated by certain hormones or substances
so that they can:
◦ Proliferate
◦ Undergo Maturation.
BFU-E: Burst Forming Unit – Erythrocyte:
◦ Give rise each to thousands of nucleated erythroid
precursor cells, in vitro.
◦ Undergo some changes to become the Colony Forming
Units-Erythrocyte (CFU-E)
◦ Regulator: Burst Promoting Activity (BPA)