Muhammad Asif Zeb Lecturer Hematology

IPMS_KMU

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!

Primitive

Definitive

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primitive system superceded by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)

Growth factors

Thank you