Page 301 - Textbook of Pathology, 6th Edition

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Figure 12.2 A normal bone marrow in an adult as seen in a section CHAPTER 12
after trephine biopsy. Bony trabeculae support the marrow-containing
tissue. Approximately 50% of the soft tissue of the bone consists of
haematopoietic tissue and 50% is fatty marrow.

The stem cells, after a series of divisions, differentiate into
two types of progenitors—lymphoid (immune system) stem
cells, and non-lymphoid or myeloid (trilineage) stem cells. The
former develop into T, B and NK cells while the latter
Figure 12.1 Sites of haematopoiesis in the bone marrow in the
adult. differentiate into 3 types of cell lines—granulocyte-monocyte
progenitors (producing neutrophils, eosinophils, basophils
poiesis in certain pathologic conditions. The spleen and liver and monocytes), erythroid progenitors (producing red cells),
can also resume their foetal haematopoietic role in certain and megakaryocytes (as the source of platelets). The develop-
pathologic conditions and is called extramedullary ment of mature cells (i.e. poiesis)—red cells (erythropoiesis),
haematopoiesis. granulocytes (granulopoiesis), monocytes, lymphocytes
In the bone marrow, developing blood cells are situated (lymphopoiesis) and platelets (thrombopoiesis) are
outside the marrow sinuses, from where after maturation considered in detail later in relevant sections.
they enter the marrow sinuses, the marrow microcirculation Myeloid haematopoiesis or myelopoiesis includes
and thence released into circulation. differentiation and maturation of granulocytes, monocytes,
erythroid cells and megakaryocytes (Fig. 12.3). The Introduction to Haematopoietic System and Disorders of Erythroid Series
HAEMATOPOIETIC STEM CELLS differentiation and maturation of each series of these cells
from stem cells are regulated by endogenous glycoproteins
Haematopoieisis involves two stages: mitotic division or called as growth factors, cytokines and hormones. These are as
proliferation, and differentiation or maturation. under:
It is widely accepted that blood cells develop from a small
population of common multipotent haematopoietic stem Erythropoietin
cells. The stem cells express a variety of cell surface proteins Granulocyte colony-stimulating factor (G-CSF)
such as CD34 and adhesion proteins which help the stem Granulocyte-macrophage colony-stimulating factor (GM-
cells to “home” to the bone marrow when infused. The stem CSF)
cells have the appearance of small or intermediate-sized Thrombopoietin
lymphocytes and their presence in the marrow can be Each of these growth factors acts on specific receptors
demonstrated by cell culture techniques by the growth of for growth factor to initiate further cell events as shown
colony-forming units (CFU) pertaining to different cell lines. schematically in Fig. 12.3.
The stem cells have the capability of maintaining their
progeny by self-replication. The bone marrow provides a BONE MARROW EXAMINATION
suitable environment for growth and development of stem
cells. For instance, if haematopoietic stem cells are infused Examination of the bone marrow provides an invaluable
intravenously into a suitably-prepared recipient, they seed diagnostic help in some cases, while in others it is of value in
the marrow successfully but do not thrive at other sites. This confirming a diagnosis suspected on clinical examination or
principle forms the basis of bone marrow (or stem cell) trans- on the blood film. A peripheral blood smear examination,
plantation performed for various haematologic diseases. however, must always precede bone marrow examination.