1. Granulocytes (These are also called 'Myeloid Cells.')
2. Monocytes
3. Lymphocytes
Some sources combine the monocytes and lymphocytes into one category and
just call them all 'mononuclear leukocytes.' (You probably are beginning to realize that
the real challenge in learning this is just learning the vocabulary.)
Granulocytes inlcude the neutrophils, eosinophils, and basophils. (It shouldn't surprise
you to learn that their cytoplasm is often filled with granules.) These are the work horses of
acute inflammation (and other processes). Make sure you learn the neutrophil. In pathology and immunology, you'll call
this same cell the PMN (polymorphonuclear leukocyte). Eosinophils are involved in allergic reactions
and parasitic infections. Another cell to mention here (although it is NOT a
granulocyte) is the Mast Cell. It's very similar to the basophil: both release histamine (and other mediators).
Some think that the mast cell is derived from the basophil. Just remember that the basophil circulates
and the mast cell is found in peripheral tissues. Other than that, they are quite similar.
Monocytes include the monoctye and the macrophage. The monocyte circulates in the blood until
it receives the signal to extravasate into the peripheral tissue. Once in the tissue, it matures
into the macrophage. It can also mature even further into other cells, but that is beyond the scope
of this course. The monocyte/macrophage is the work horse of chronic inflammation.
Lymphoctyes are often overlooked when we consider blood, but they are white blood cells.
Indeed, they originate in the bone marrow and are derived from the same stem cell as the rest
of the erythrocytes and leukocytes. These are the T-cells and B-cells that direct the immune
system and produce antibodies, respectively. They are the central cells in our cell-mediated
and humoral (antibody) defense mechanisms. Also keep in mind that the B-cell can mature into
the plasma cell.
If you remember nothing else... Know that as a rule of thumb, bacterial infections cause
granulocytosis and viral infections cause lymphocytosis. There are exceptions to this, but this
is a very basic (and important) concept. You'll learn more about why this is in immunology.
This should give you a good place to start. Spend some time learning the pathways from the original
stem cell and realize that it gives rise to all these cells. It will be well worth your time to
really learn this. You will be glad that you did (just ask any pathology student).
Your goal here should be more than to just get by.
Good Luck!
