Monocytes are a type of white blood cell (leukocyte) that are produced from the pluripotent stem cells found in the bone marrow.
Once they are produced in the bone marrow, they remain there for a very short period of time (less than 24 hours) before moving to the circulatory system and the marginating pool. They also remain in these environments for a few days (2 to 3 days) and ultimately migrate to various tissues where they change into macrophages.
While monocytes are the largest white cells, they only make up about 5 percent of the total leukocytes in circulation. However, their numbers will increase during an infection (when bacteria or protozoa invade body tissues and cause inflammation).
Unstained, the different types of leukocytes are almost impossible to identify. However, staining a blood smear with such stains as Wright-Giemsa stain can help increase contrast and thus be in a position to differentiate the different types of white blood cells. Here, this technique will be used to identify monocytes.
* Fix the thin slide with acetone-free methanol before staining and allow it to dry completely
When viewed under the microscope at high power, the slide shows numerous red blood cells that appear to have a space in the middle. However, students will also be able to see several monocytes that will appear spherical or bean shaped with a dark material inside.
Compared to other leukocytes, monocytes will appear larger therefore setting them apart.
As mentioned, monocytes are spherical in shape or may appear amoeboid. They are large in size and have a large nucleus that is usually bean shaped. This characteristic differentiates monocytes from neutrophils, which have several lobes with a divided nucleus. In tissues, monocytes transform to macrophages.
As macrophages, monocytes play an important role of eliminating foreign material, tumorous cells and microorganisms through a process known as phagocytosis.
* Essentially, phagocytosis involves the cell engulfing foreign material or microorganisms in to the cell vacuole where they are ingested and destroyed by enzymes.
Depending on the tissue in which they reside, macrophages will have different names.
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