The hematopoietic system is the organ system comprising the blood and tissues responsible for blood cell generation through the process of hematopoiesis (see figure illustrating ).
Normal hematopoiesis. BFU-E, burst-forming unit-erythroid; CFU, colony-forming unit (-Baso, -basophil; -E, -erythroid; -EO, eosinophil; -G, granulocyte; -GM, granulocyte macrophage; -GEMM, -granulocyte/erythrocyte/macrophage/megakaryocyte; -L, leukemic; -M, macrophage; -MK, megakaryocyte progenitor; -S, -spleen).
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The cellular elements of blood deliver oxygen to cells (RBCs), protect against foreign organisms and antigens (WBCs), and initiate coagulation (platelets), whereas the noncellular component of blood (plasma) supplies cells with water, electrolytes, nutrients, and hormones and removes waste products.
Because of the hematopoietic system's diversity, its diseases are best discussed from a functional perspective. Functions can be classified as either appropriate responses to abnormal situations (eg, leukocytosis and left shift in response to inflammation) or primary abnormalities of the hematopoietic system (eg, pancytopenia from bone marrow dysfunction). Furthermore, abnormalities can be quantitative (ie, too many or too few cells) or qualitative (ie, abnormalities in function). (Also see The Biology of the Immune System.)
For More Information
Lattimer KS, ed. Duncan and Prasse's Veterinary Laboratory Medicine: Clinical Pathology. 5th ed. Wiley-Blackwell; 2011.
eClinpath. Physiology: hematopoiesis.
Also see pet owner information regarding an introduction to blood disorders in dogs.
