Blood cells

[Ref: WG21:p517-522; PK1:p235]

Bone marrow

In foetal life, blood cells are formed in liver (mainly) and spleen
* From 6 weeks to 7 months
* Peak at 5 months

From 6-7month in foetal life
--> Bone marrow becomes the main source of haemopoiesis

By age 18-20

• Active bone marrow are only in
  * Central skeleton (vertebrae, pelvis, ribs, sternum, skull)
  * Proximal end of femur and humerus
• Rest become infiltrated with fat (yellow marrow)

RBC vs WBC

75% of the bone marrows belong to the white cell producing myeloid series

25% of the bone marrow are maturing red cells

NB:

• RBC is about 500 times higher in concentration than WBC due to its longer lifespan

Differentiation

Pluripotential stem cells
--> Progenitor cells (committed stem cells)
--> Blood cells

Separate pools of progenitor cells for

• Megakaryocytes
• Lymphocytes
• Erythrocytes
• Eosinophils
• Basophils
• Neutrophils and monocytes (arise from a common precursor)

Stem cells also produce

• Osteoclasts
• Kupffer cells
• Mast cells
• Dendritic cells
• Langerhans cells

Progenitor cells are produced under the influence of

• IL-1
• IL-6
• IL-3
• GM-CSF