Page 18 - Essential Haematology

4 / Chapter 1 Haemopoiesis

Multiplication
Self Differentiation
renewal

(a)

Mature
cells

Stem Multipotent Recognizable
cells progenitor cells committed
marrow
(b) precursors

Figure 1.3 (a) Bone marrow cells are increasingly differentiated and lose the capacity for self - renewal as they

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mature. (b) A single stem cell gives rise, after multiple cell divisions (shown by vertical lines), to > 10 mature
cells.

Stem cell

Extracellular
matrix

Macrophage
Fat cell

Endothelial cell Fibroblast

Adhesion molecule Ligand
Growth factor Growth factor receptor

Figure 1.4 Haemopoiesis occurs in a suitable microenvironment ( ‘ niche ’ ) provided by a stromal matrix on which
stem cells grow and divide. There are specifi c recognition and adhesion sites (see p. 13 ); extracellular glycopro-

teins and other compounds are involved in the binding.

The stromal cells include adipocytes, fi broblasts, In addition, stromal cells secrete several growth
osteoblasts, endothelial cells and macrophages and factors necessary for stem cell survival.
they secrete extracellular molecules such as collagen, Mesenchymal stem cells , also called multipo-
glycoproteins (fibronectin and thrombospondin) tent mesenchymal stromal cells or adherent stromal

and glycosaminoglycans (hyaluronic acid and chon- cells, are critical in stromal cell formation. Together
droitin derivatives) to form an extracellular matrix. with osteoblasts they form niches and provide the