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.



  • Hemopoiesis depends on 3 important components:
  • the bone marrow stroma (Local control)
  • the hemopoietic stem and progenitor cells
  • the hemopoietic growth factors (Humoral control)

Stem Cell Theory

 All the blood cells are produced by the bone marrow.

They all come from a single class of primitive mother cells called as:


These cells give rise to blood cells of:

Myeloid series: Cells arising mainly from the bone marrow.

Lymphoid series: cells arising from lymphoid tissues.


Stem Cells

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”


Stem Cells: Types

Pluripotent Stem cells:

Has a diameter of 18 – 23 μ.

Giving rise to: both Myeloid and Lymphoid series of cells

Capable of extensive self-renewal.

Myeloid Stem cells: Generate myeloid cells:


Granulocytes: PMNs, Eosinophils & Basophils.


Lymphoid Stem cells: Giving rise only to:

Lymphocytes: T type mainly.


Properties of stem cells

Extensive proliferative capacity 
Cell cycle status 
Surface Markers 
Interact with microenvironment 

Sites of hemopoiesis

Yolk sac

Liver and spleen

Bone marrow

–Gradual replacement of active (red) marrow by inactive (fatty) tissue

–Expansion can occur during the increased need for cell production.


Sites of hemopoiesis

Active Hemopoietic marrow is found, in children throughout the:

Axial skeleton:





  • 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

Sites of Hemopoiesis

  • Hemopoiesis starts as early as yolk sac development.
  • 2-3 weeks after fertilization 3 layers are developed (ecto, meso, and endoderm)
  • Hemoangioblast which is derived from the mesoderm


In the embryo

2 week old embryo, hematopoiesis begins in yolk sac.
By 2 month old fetus, granulocyte and megakaryocyte production.
4th month, lymphocytes production.
5th month, monocytes were produced.
In the 3rd to 7th month of fetal life Hemopoietic stem cells will migrate to the liver and spleen, where hemopoiesis starts there and hemopoiesis is still mainly erythropoietic in nature, with minimal granulopoiesis.


The bone marrow (BM)

  • The stem cells then migrate to the bone marrow (BM) where hemopoiesis starts and continue all over the life. In the bone marrow, all types of blood cells are formed which include:
  • RBCS
  • Granulocytes: Neutrophils, Eosinophils, Basophils
  • Lymphocytes
  • Monocytes and macrophages
  • Platelets


The lifespan of blood cells

Cell type

Approximate lifespan

Red Cells

120  days


t½ 6 hours


7 days


t½ 10 days


Extramedullary Hemopoiesis

When required, yellow marrow can be replaced by red marrow.
Liver & spleen can aslo resumed.
This will multiply the production by 6.
Remark that Hemopoiesis within the marrow is called intramedullary or medullary hemopoiesis.

Hematopoietic Inductive Microenvironment

The stromal matrix plays an important role in presenting growth factors and nutrients to developing blood cells.
The  most immature cells have receptors which bind them to proteoglycan molecules on the matrix and to receptors on the stromal cells (i.e. macrophages, fibroblasts, fat cells and endothelial cells)
There are lineage specific regions ( "niches" ) which provide the molecular basis  for homing of transplanted stem cells.

The unique supportive microenvironment stem cell niche       - regulates proliferation and differentiation      - supports survival and inhibits apoptosis

Similar principles apply to malignant stem cells in myeloid leukemias.

The sinusoids are lined with specialized endothelial cells which play an important role by producing factors which regulate growth and differentiation.


Stromal Cells of BM

Endothelial cells
Fat cells

Haemopoietic growth factors

The haemopoietic growth factors are glycoprotein hormones that regulate the proliferation and differentiation of haemopoietic progenitor cells and the function of mature blood cells.

T lymphocytes, monocytes, macrophages and stromal cells are the major sources of growth factors except for erythropoietin, 90% of which is synthesized in the kidney and thrombopoietin, made largely in liver.

Haemopoietic growth factors

Granulocyte-Macrophage colony stimulating factor
Macrophage colony stimulating factor
Erythropoiesis stimulating hormone
(These factors have the capacity to stimulate the proliferation of their target progenitor cells when used as a sole source of stimulation)
Stimulates megakaryopoiesis


Haemopoietic growth factors

IL 1 (Interleukin 1)
IL 3
IL 4
IL 6
IL 9
IL 11
SCF (Stem cell factor, also known as kit-ligand)

Cytokines have no (e.g IL-1) or little (SCF) capacity to stimulate cell proliferation on their own, but are able to synergise with other cytokines to recruit nine cells into proliferation.

Stem Cells

Stem Cells: undifferentiated cells that give rise to all of the bone marrow cells.
Only 0.5% of all marrow nucleated cells.
Multipotential precursors.
High self-renewal – give rise to daughter stem cells that are exact replicas of the parent cell.
Not morphologically distinguishable At any time, the majority of stem cells (95%) are out of the cell cycle (they are in G0 mode/phase, also called quiescent).


Progenitor cells of the BM

Stem cells which undergo differentiation.
Limited self-renewal ability.
Multipotential but Gradually they become unilineage or committed progenitor cell.
~3% of total nucleated hematopoietic cells of bone marrow

Progenitor cells of the BM

Form colonies of cells in semisolid media in vitro – described as colony forming units (CFU).

CFU-GEMM (granulocytic, erythrocytic, monocytic,megakaryocytic,CFU-GM,CFU-Mk, etc. )

Survival and differentiation of progenitor cells influenced by growth regulatory glycoproteins, called cytokines – include interleukins, colony stimulating factors

Morphology of stem cells and progenitor cells

Stem cells & progenitor cells are not recognized morphologically but all look like small mononuclear lymphocytes.

Maturing blood cells

Majority of cells (>95%)

lose adherence receptors,  become deformable.

migrate through cytoplasm of  lining endothelial cell to enter  sinusoids.

Platelets are the exception.

Megakaryocytes   form  part of the sinusoidal wall.  They form long processes of proplatelets which fragment into nascent platelets.



Regulated physiological cell death
Morphological evidence
Enzymatic digestion of DNA and cell disintegration

Two major pathway of activation of caspases
Membrane signalling
Cytochrome c release


  • Eosinophils
  • Coarser & more deeply red staining granules
  • Rarely more than two lobes of nucleus
  • Special role in allergy, inflamation & parasite infection
  • Basophils
  • Occasionally seen
  • Dark cytoplasmic granules
  • Role in hypersensitivity response
  • Give rise to mast cells



  • Larger than lymphocyte
  • Oval or indented nucleus
  • Monocytes >>>>to macrophage
  • Specific function depends on the tissue type


Immunologically competent cells
Primary lymphoid organs
Bone marrow
Secondary lymphoid organs
Lymph nodes
Lymphoid tissues
B and T lymphocytes
NK killer cells



  • Platelet play a major role in primary hemostasis
  • Life span 7-10 days
  • Production, fragmentation of cytoplasm
  • Megakaryocytes undergoes endomitotic division
  • 1/3 in spleen



  • Normal haemopoiesis is necessary for the survival
  • It is under the control of multiple factors
  • Normal bone marrow environment is necessary for normal haemopoiesis
  • Decreased production results in cytopenias.




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