40 – Hematopoietic System

This chapter discusses about toxicologic pathology of hematopoietic system. Toxic responses in humans and animals may involve the hematopoietic system directly or indirectly through injury to other body systems. Thus, examination of the blood and bone marrow is a standard procedure of dose-response studies utilizing laboratory species as well as in human and animal clinical situations where systemic toxicities are the suspected cause of disease. Primary or direct effects on hematopoietic cells occur as with myeloid hyperplasia in response to lithium; secondary or indirect effects are because of toxic injury to a major organ system. In a similar manner, a direct toxic effect on erythropoiesis by heavy metals may result in anemia, whereas anoxia of various causes may have the indirect result of causing erythrocytosis. Much of the classical information learned about the hematopoietic system has been derived from studies on the dog and pig, whereas documentation of toxic effects on the hematopoietic system has largely been derived from studies on smaller laboratory species. This chapter discusses about morphologic and kinetic background for understanding toxic effects on the hematopoietic system and demonstrates the way alterations in patterns of maturation in hematopoietic production can point to the mechanism of injury, its degree, and possible causes. Stem cells today are universal tools not limited to body systems but defined on the basis of the environmental and humoral factors that dictate their direction of differentiation. Instead of a huge reserve of cells in the marrow, it appears that nature has been conservative and the marrow granulocyte reserves are no larger than the cohort normally present in the peripheral blood. Therefore, it is important that professionals develop newer systems to assess the subtle, morphologic changes in blood that suggest that the hematopoietic system is under stress before cellular levels are above or below normal ranges.