HAEMATOPOIESIS & BONE
MARROW
Definition
• A process by which mature blood cells
develop from precursors
• Adults – takes place in the bone marrow ,
skull,sternum, vertebral column, pelvis and
proximal ends of long bones
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Before adulthood several sites are present
Early embryo – yolk sac
3 -7 months the spleen is the major site
During bone formation 4 – 5 months,
granulocytes & platelets formation begins
in bone marrow
• Erythropoesis - 7 months
• By birth haemopoesis is almost exclusive
to bone marrow
Monophyletic theory
• Lineage of blood cell types is derived from
a single primitive stem cell type –
multipotential (pluripotential) stem cells
• It replicates slowly differentiating into 5
discrete type of unipotential stem cells
Each is committed to different
developmental lineage:
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Erythrocytes
Granulocytes
Lymphocytes
Monocytes
platelets
• In vitro cultures progenitor cells are
described colony forming units CFU
• Division is modulated by hormones called
poietins e.g erythropoietin and locally
produced colony stimulating factors &
interleukins
Bone marrow
• 2 types
• Yellow – plenty of adipocytes
• Red - heamatogenous
Red bone marrow
• Stroma – meshwork of reticular cells and
delicate web of reticular fibers. These
contain heamatopoietic cells and
macrophages
Collagen types I & III, fibronectin,laminin,
proteoglycans
• Sinusoidal capillaries
discontinuous type
discontinuous basal lamina
discontinuous layer of reticular cells and
loose network of fibers support the
capillaries
• Adipocytes
reticular cells that accumulate lipids
become adipocytes