Credit: http://commons.wikimedia.org/wiki/File:AML-M5B.jpgMore commonly known as white blood cells, leukocytes are the only type of formed elements that is a complete cells, having organelles and nuclei. When compared to the red blood cells, leukocytes are far less numerous.
General Structure and Functional CharacteristicsCredit: http://www.nature.com/icb/journal/v85/n2/fig_tab/7100019f1.html
Leukocytes are the body’s own personal army. They are in the frontlines of our defense against disease and helps in protecting the body against viruses, bacteria, toxins and parasites. Because of such enormous responsibility, the white blood cells have special functional characteristics.
Red blood cells carry out their roles and function within the confines of the bloodstream. White blood cells are special since they can perform diapedesis, an ability to move out of the capillaries. The leukocytes simply use the circulatory system’s branching network of vessels as transport to various areas of the body where they are needed.
Adhesion molecules or selectins releases a signal that prompts the leukocytes to leave the bloodstream and arrive at a specific location where their services are needed. As the leukocyte leaves the bloodstream, it reaches its destination by way of amoeboid motion. They can pinpoint the location damaged tissues or infection by way of following chemical trails released by the damaged cells.
In the event that the white blood cells are needed for action, the body’s response is to double the production of white blood cells. Within only a few hours, twice the number of white blood cells will be present in the blood stream.
Granulocytes are one of the two major categories of leukocytes. They contain membrane-bound cytoplasmic granules and include basophils, eosinophils and neutrophils. All of them have the same spherical shape. When compared to erythrocytes, they are much larger but lives shorter. Functionally, all of the granulocytes are considered to be phagocytes to a greater or lesser degree.
Neutrophils account for almost 50-70% of the entire white blood cell population. They derived their name from being neutral, taking up both basic and acidic dyes. Neutrophils are active phagocytes and are chemically attracted to inflammation sites. Neutrophils are branded as the body’s bacteria slayers and their number will increase exponentially during acute infections.
The most important role that eosinophils play is its role as the leader that counterattacks against parasitic worms such as roundworms and flatworms, which are too large for the Neutrophils to eat or to phagocytized. The secondary role that eosinophils play is it lessens the severity of allergies by its ability to inactivate some inflammatory chemicals being released.
Basophils account for only 1% of the total white blood cell population, making it the rarest. The cytoplasm of basophils has granules that contain histamine. Histamine is an inflammatory chemical that has the ability to dilate blood vessels and attracts other WBC to the site.
Agranulocytes are special WBC that lacks cytoplasmic granules. It includes monocytes and lymphocytes. Although physically the two cells look the same, they do have functional differences.
Lymphocytes account for more than 25% of the WBC population, making it the second most abundant leukocyte in the blood. Of the 25% that exists throughout the body, only a small portion navigates the bloodstream. The name lymphocytes are derived because they are firmly enmeshed in lymphoid tissues; lymphocytes play an important role in our immunity.
As the monocytes leave the blood stream, they transform into highly mobile macrophages which has remarkable appetites. Macrophages are very crucial in the defense of the body against viruses and certain bacteria because they are actively phagocytic.