Merck Manual

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Overview of Hematopoietic System in Animals


Susan M. Cotter

, DVM, DACVIM, Cummings School of Veterinary Medicine, Tufts University

Reviewed/Revised May 2019 | Modified Oct 2022
Topic Resources

Blood supplies cells with water, electrolytes, nutrients, and hormones and removes waste products. The cellular elements supply oxygen (RBCs Red Blood Cells in Animals The function of RBCs is to carry oxygen to the tissues at pressures sufficient to permit its rapid diffusion. This is accomplished through the following mechanisms: a carrier molecule, hemoglobin... read more ), protect against foreign organisms and antigens (WBCs White Blood Cells in Animals The principal function of phagocytes is to defend against invading microorganisms by ingesting and destroying them, thus contributing to cellular inflammatory responses. There are two types... read more ), and initiate coagulation (platelets Platelets in Animals Platelets form the initial hemostatic plug whenever hemorrhage occurs. They also are the source of phospholipid, which is needed for the interaction of coagulation factors to form a fibrin clot... read more Platelets in Animals ). Because of the diversity of the hematopoietic system, its diseases are best discussed from a functional perspective. Function may be classified as either normal responses to abnormal situations (eg, leukocytosis and left shift in response to inflammation) or primary abnormalities of the hematopoietic system (eg, pancytopenia from marrow failure). Furthermore, abnormalities may be quantitative (ie, too many or too few cells) or qualitative (ie, abnormalities in function). (Also Veterinary.see The Biology of the Immune System The Biology of the Immune System .)

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