1) Hematopoiesis is the production and development of blood cells, including erythrocytes, leukocytes, and thrombocytes, which begins in the fetal liver and spleen and later occurs mainly in the bone marrow. 2) There are two main stages of hematopoiesis - the primitive stage which occurs in the yolk sac, and the definitive stage which occurs in the embryo itself and continues throughout adult life in the bone marrow. 3) Hematopoiesis is regulated by hematopoietic stem cells in the bone marrow, which can self-renew and differentiate into various blood cell types through committed progenitor cells and growth factors.

1. Muhammad Asif Zeb
Lecturer Hematology
IPMS_KMU

2. Things to learn:-
Hematopoiesis or hemopoiesis
Site of Hemopoiesis
Stages of hemopoiesis,
Regulating factors on hemopoiesis

3.  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!

4.  Primitive
 Definitive

5.  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

6. 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primitive system superceded by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)

7.  Throughout fetal life, the liver is the chief organ
for production of myeloid and erythroid cells
After birth, BONE
MARROW becomes
main
hematopoietic
organ.

8. • Mesoblastic stage-
in the yolk sac
Starts at 2 weeks of intrauterine life
intravascular
• Hepatic stage-
2-7 months
Both liver and spleen

9. • 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

12.  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.

13. 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.

14.  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”

15. PLURIPOTENT STEM CELL
STEM CELL
MULTIPLICATION COMMITTMENT
COMMITTED
STEM CELL
COMMITTED
STEM CELL
MULTIPLICATION
PROGENITOR
CELL
CFU: COLONY
FORMING UNIT

16. 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.

17. • 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

19.  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.

20.  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)

23. Growth factors

27. Thank you