OVERVIEW OF HAEMATOPOIESIS

Question 1

INTRODUCTION

Answer 1

Haemopoiesis is defined as the formation, development and differentiation of blood cellular components.
Includes: Erythropoiesis, Myelopoiesis(granulocytes and monocytes), Lymphopoiesis and thrombopoiesis

Question 2

HAEMOPOIETIC SITES

Answer 2

3phases, the mesoblastic, hepatic and myeloid phase
The mesoblastic phase- 2nd week to 3rd month (cells cluster in the yolk sac)

The hepatic phase- the 2nd month to the 7th month ( mainly the liver with the supplementation of the spleen)

The myeloid phase- from the 6th month to adult life, The red bone marrow

In infancy all the bone marrow is haemopoietic
but during childhod there is progressive fatty replacement of the marrow throughout the long bones
Hence in Adults only the central skeleton, and the proximal end of the femurs and humeri have haemopoietic marrows

Question 3

THE HAEMOPOIETIC STEM CELL AND BONE MARROW

Answer 3

Stages in haemopoietic cell development 
Lineage selection
Physical maturation
Functional maturation
And
Cell death

The haemopoietic stem cell is the starting point of haemopoiesis
Capacity of cell reproduction

Pluripotent i.e it can generate different types of tissues

THE BONE MARROW
It provides suitable environment for the stem cells to survive and grow
Composed of Stromal cells and Microvascular network

BONE MARROW STROMAL CELLS

• Consists of adipocytes, fibroblastss, endothelial cells and macrophages
• they form extracellular matrix composed of collagen, glycoproteins and glycosaminoglycans
• secrete growth factor for stem cell survival

Question 4

THE PROGENITOR CELLS & PRECURSORS

Answer 4

Cell differentiation occurs from stem cells via haemopoietic progenitors, they are formed as a result of loss of one or more developmental potential of the HSC

Characteristics of Progenitor cells

• loss of pluripotency
• lack of capacity of self renewal
• higher fraction of cells transversing the cell cycle
• 2 types: multipotential and commited

They’re either Myeloid progenitor or Lymphoid progenitor

Not morphologically identifiable but through in vitro techniques

THE PRECURSORS
By the way are morphologically identifiable and they eventually develop to become mature cells

Question 5

REGULATION OF HAEMOPOIESIS & HAEMOPOIETIC GROWTH FACTORS intro

Answer 5

A balance between cell production and cell death is required
When necessary such as In haemorrhage, cell production will exceed cell death

Haemopoietic growth factors are glycoproteins that regulate the proliferation and differentiation of progenitor cells

They may act locally at site of formation or circulate in plasma. They can cause; cell proliferation, cell differentiation, maturation, prevent apoptosis and affect function of normal cells

Major sources of growth factors;
- stromal cells
- T-lymphocyte
- monocytes ( macrophages)
Kidneys produce erythropoietin and Liver produces Thrombopoietin

Question 6

HAEMOPOIETIC GROWTH FACTORS

Answer 6

Include:

GM-CSF (Granulocyte Macrophage Colony Stimulating factor)

M-CSF (Macrophage Colony Stimulating Factor)

Erythropoietin (Erythropoiesis stimulating hormone)

Thrombopoiesis (Megakaryopoisis stimulating hormone)

Cytokines- InterLeukin, SCF(stem cell factor) or Kit-ligand

Question 7

GENERAL CHARACTERISTICS OF HAEMOPOIETIC GROWTH FACTORS

Answer 7

Can act in low concentration 
Can affect more than one lineage
Show synergistic action
Act on neoplastic and normal cells
Act hierachically
Produced by many cells
Usually active on stem/progenitor cells and on functional end cells

Question 8

CLINICAL APPLICATION OF GROWTH FACTORS

Answer 8

Treatment of anemia

Treatment of neutropenia

Treatment of thrombocytopenia

Haemopoietic stem cell transplantation