Blood cells form and develop mostly in the bone marrow, that is, the tissue located in the cavities of bones. Blood performs a variety of important functions as it circulates throughout the body. It delivers oxygen and vital nutrients (such as vitamins, minerals, fats, and sugars) to the tissues. It carries carbon dioxide to the lungs to be exhaled and waste products to the kidneys and liver to be eliminated from the body. It transports hormones, which are chemical messengers, to various parts of the body, allowing those parts to communicate with each other. Blood also includes cells that fight infection and control bleeding.

There are 3 cellular elements of blood: red blood cells, white blood cells, and platelets. Basically, red blood cells supply the body with oxygen, white blood cells protect against infection, and platelets start the formation of blood clots.

Types of Blood Cells*
*See chapter text for descriptions and functions.

Blood is a complex mixture of plasma (the liquid component), red blood cells, white blood cells, and platelets.

Blood disorders are quite diverse. They can occur as normal responses to abnormal situations; for example, a significant increase in the number of white blood cells in response to an infection or disease. They may also occur as primary abnormalities of the blood; for example, a deficiency of all cellular elements of the blood due to bone marrow failure. Furthermore, abnormalities may be quantitative (too many or too few cells) or qualitative (abnormalities in the way cells function). It is helpful to understand what the names of some blood disorders mean, as they often provide a description of the disorder itself (see Blood Disorders of Dogs: Suffixes Used in Names of Blood Disorders).

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Suffixes Used in Names of Blood Disorders Suffix Definition Example “philia” Increase in blood levels of that type of cell Neutrophilia “osis” An abnormal increase in blood levels of that type of cell; can also refer to a disease process Lymphocytosis “penia” Decrease in blood levels of that type of cell Neutropenia “lysis” Destruction of that type of cell Hemolysis “emia” Denotes the presence of a substance in the blood Polycythemia “stasis” To stop or stabilize Hemostasis

Just as there are various blood types in humans, there are multiple blood types in dogs, cats, horses, and other animals. A few blood banks for animals have been established. Like human blood banks, they depend on donated blood and can provide type-matched blood for use in emergencies or surgeries.

Last full review/revision July 2011 by Peter H. Holmes, BVMS, PhD, Dr HC, FRCVS, FRSE, OBE; Nemi C. Jain, MVSc, PhD; David J. Waltisbuhl, BASc, MSc; Michael Bernstein, DVM, DACVIM; Karen L. Campbell, MS, DVM, DACVIM, DACVD; Timothy M. Fan, DVM, PhD, DACVIM; Wayne K. Jorgensen, BSc, PhD; Sarah E. Payne, DVM, DACVIM