Chapter 8 - Hematopoiesis
Hematopoiesis is the development and formation of blood cells. Blood cells arise from hematopoietic stem cells rather than from the division of mature blood cells. This complex process involves the formation of many intermediate stages and cell types that become progressively more differentiated.
In adults, hematopoiesis occurs in bone marrow and generates hundreds of millions of new blood cells every day.
Bone marrow is a specialized connective tissue composed of developing blood cells within a supportive stroma of reticular tissue. It is found between the trabeculae of the spongy portions of bones.
Bone Marrow Smear
Similar to blood smears, the histology of developing blood cells is studied in bone marrow smears prepared by spreading a small amount of bone marrow into a thin layer on a microscope slide. This separates the individual cells so their morphology can be more easily examined.
A high resolution scan from the zone of best morphology of a bone marrow smear was obtained using an oil immersion 60x lens (NA 1.4). The increased resolution allows the morphology and staining characteristics of the different cell types to be more easily examined.
Erythropoiesis is the development of red blood cells. As the precursor cells mature, they decrease in size, chromatin becomes more condensed, nuclei are eventually extruded, and cytoplasm changes in color from blue to pink. Granules are never seen in the lineage of red blood cells.
Granulopoiesis is the development of granulocytes that comprise neutrophils, eosinophils, and basophils. Key events in the maturation of granulocytes are the production of azurophilic granules, specific granules, and nuclear lobulation.
Lymphopoiesis and monopoiesis are the development of lymphocytes and monocytes, respectively. Unlike granulocytes, they do not contain specific granules or show nuclear lobulation.
Thrombopoiesis is the development of platelets. The largest cells found in bone marrow are megakaryocytes which give rise to platelets.
This diagram allows the morphology and staining characteristics of the different stages of blood cell development to be compared.
Bone marrow contains a survival niche that allows plasma cells to continuously secrete antibodies with a life span of months to years.
Viewing of these slides is not required. However, they demonstrate the variability seen between different preparations of bone marrow smears.