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Overview
Remember from the last lesson, the white blood cells of the immune system are composed of 5 major types:
- neutrophils,
- eosinophils,
- basophils,
- monocytes, and
- lymphocytes.
They can also be categorized into groups by their characteristics or actions such as phagocytes, macrophages, and granulocytes.
Each of these cells plays specific roles in the fight against invaders and the clean-up of damaged cells. Image 1 illustrates these cells and highlights a major role each cell type has. You will also notice in this image that some of the WBCs, white blood cells, are grouped as granulocytes and some are grouped as agranulocytes.
Granulocytes are white blood cells with granules in their cytoplasm that secrete chemicals. WBCs without these granules are grouped as agranulocytes “a” is a prefix in this word meaning “without” .
All WBCs, except for the lymphocytes, are categorized as phagocytes. Phagocytes are any cell that can engulf (or “eat”) another cell, invading organism, or particle (See image 2)
Monocytes are also categorized more specifically as a macrophage type of white blood cell that engulfs and digests by phagocytosis cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific to healthy body cells on its surface .
Check your understanding:
-All WBCs are categorized as “phagocytes” except for _______.
-Why are eosinophils, monocytes, basophils, and neutrophils considered phagocytes?
-Monocytes are not only in the category of phagocytes, but also are considered to be _________ due to the fact that they have one nucleus and have the ability to “eat” cancer cells, foreign substances, and microbes.
-Basophils contain granules that can secrete chemicals such as histamine. This characteristic classifies them as ____________.
All blood cells, including WBCs, originate from a hematopoietic stem cell in the bone marrow as mapped in Image 3. You will notice from this map that phagocytic white blood cells develop from a myeloid stem cell and lymphocytes develop from a lymphoid stem cell.
Check your understanding:
-What is the difference between the origination of lymphocytes from all other WBCs?
Dendritic cells are not a type of WBC, but do play a role in defense through their ability to engulf invading organisms. After engulfing, they present the invaders antigens a protein molecule capable of inducing an immune response to the body’s WBCs to activate the immune system. This process of presenting an invaders antigens is called “antigen presentation.”
Check your understanding:
-How would you describe antigen-presentation process?
