4.3 Hematologic System

Overview

The hematologic system is responsible for the production of blood cells and consists of the bone marrow and blood cells. Together with the heart, the blood and blood vessels make up the cardiovascular system.

Blood is made up of cells, proteins and a liquid component. The cellular elements include red blood cells (RBCs), white blood cells (WBCs), and platelets.

The function of the blood is to carry oxygen, nutrients and waste products (Betts et al., 2013). It is also important in defence, regulating body temperature, and maintenance of homeostasis.

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Structures

Blood Cells

Red blood cells (RBC) are also known as erythrocytes. They carry oxygen and carbon dioxide and are the most common cells in the blood.

White blood cells (WBC) or leukocytes are identified as neutrophils, monocytes, lymphocytes, eosinophils, and basophils. These WBCs play different roles in the blood, including protecting the body from viruses, parasites, and bacteria.

Platelets: small, irregularly shaped fragments of cells. They are involved in blood clotting.

Plasma: the cell-free component of blood that contains clotting factors. It consists of water, proteins, nutrients, and hormones.

Serum: the cell-free component of blood that is left over after blood has clotted. It does NOT have clotting proteins because they have all been used up.

Common Blood Pathological Conditions

Anemia: A condition in which the number of red blood cells (RBCs) or hemoglobin is lower than normal

Cyanosis: An abnormal condition of “blue” characterized by blueish lips and nailbeds, typically caused by low oxygenation

Hemolytic: A disorder in which red blood cells are destroyed faster than they can be replaced

Hemorrhage: Excessive or uncontrolled bleeding from the blood vessels; can be internal (bleeding inside the body) or external (bleeding outside the body)

Leukemia: A type of cancer involving an abundance of leukocytes; affects the body’s blood-forming tissues, including the bone marrow and lymphatic system

Leukopenia: Lower-than-normal numbers of white blood cells

Pancytopenia: A condition in which all the cells in the blood are lower in number than normal

Sepsis: A potentially life-threatening condition that occurs when the body’s response to an infection damages its own tissues

Common Procedures

Bone marrow biopsy: A diagnostic test of a sample of bone marrow

Chemistry (“chem”) panel: A group of tests that measures liver and kidney enzymes, as well as electrolytes, glucose, and other proteins

Complete blood count (CBC) and differential: A collection of blood tests that count the different types of blood cells (RBCs, WBCs, and platelets) and the different types of WBCs (neutrophils, lymphocytes, monocytes, eosinophils, and basophils)

Hematocrit: A lab test that measures the percentage of red blood cells in a sample of whole blood; this represents how much of the blood is made up of red blood cells by volume

Vasodilator: A substance that dilates blood vessels

Venipuncture: Puncturing a vein to withdraw blood or administer medication or fluids

Additional Hematologic Terminology

Anticoagulant: A substance that slows or inhibits blood clotting

Blood pressure: The force exerted by blood on the walls of the blood vessels or the chambers of the heart

 

Blood smear: A small amount of blood spread on a slide for examination under a microscope

 

 

Hematology: The study of blood

Hematoma: A collection of blood outside the blood vessels, usually caused by trauma, disease, or surgery

Hemoglobin: A protein found in red blood cells that carries oxygen; abnormal amounts indicate a blood disorder

Intravenous: Pertaining to within the veins

Thrombus: a blood clot

References

Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., Kruse, D. H., Korol, O., Johnson, J. E., Womble, M., & DeSaix, P. (2013). Anatomy and physiology. OpenStax. https://openstax.org/details/books/anatomy-and-physiology, licensed under CC BY 4.0

Hamor, R. E. (2023). The conjunctiva in animals. In Merck veterinary manual: Eye diseases and disorders. Merck. https://www.merckvetmanual.com/eye-diseases-and-disorders/ophthalmology/the-conjunctiva-in-animals

Hinic-Frlog, S. (n.d.). Introductory animal physiology. University of Toronto Mississauga. https://ecampusontario.pressbooks.pub/introanimalphysiology, licensed under CC BY 4.0

Jennings, R., & Premanandan, C. (2017). Veterinary histology. Ohio State University. https://ohiostate.pressbooks.pub/vethisto, licensed under CC BY-NC 4.0

Molnar C., & Gair, J. (2021). Concepts of biology – 1st Canadian edition. BCcampus. https://opentextbc.ca/biology/, licensed under CC BY 4.0

Woodward, M. (2020). Otitis externa in animals. In Merck veterinary manual: Ear disorders. Merck. https://www.merckvetmanual.com/eye-diseases-and-disorders/ophthalmology/the-conjunctiva-in-animals

Image Credits
(images are listed in order of appearance)

Red blood cells (RBCs), platelets and white blood cells or leukocyte (neutrophil) on PBS by Ajay Kumar Chaurasiya, CC BY-SA 4.0

Serum-separation tube by Spiritia , CC BY-SA 4.0

1091 Composition of Blood by OpenStax College, CC BY 3.0

Complete blood count and differential by SpicyMilkBoy, CC BY-SA 4.0

Peripheral blood smear – stained and unstained by Coinmac, CC BY-SA 3.0

BP monitoring by Kelly Robertson, NorQuest College. Used with permission.