Video 9 White Blood Cells Types and Functions

09) White cell types and functions

While white cells vary in size, generally they are the largest cell type found circulating in the blood. They live in the lymph system, where many are stored. They circulate in the blood. And they can be found in tissues throughout the body, always ready to spring into action. As a group all the different types of white cells together make up less than one percent of total blood volume. Some white cells live just 18 hours, while others live for many years.

Now let's take a closer look at the different types of white cells and the role each plays in protecting the body. There are five major groups of leukocyctes: basophils, neutrophils, eosinophils, monocytes and lymphocyctes. Each of these cells is equipped to match a specific type of antigen or invader.

Let's start with basophils. These white cells defend against parasites and bacteria by releasing histamine and heparin, which is a blood thinning substance. Histamines are what cause allergy symptoms, such as itchy skin, watery eyes and a runny nose. Basophils are not antigen specific, meaning they don't have to determine what the invading substance is before taking action. They spring into action any time a foreign substance is detected.

Next are neutrophils. This group of white cells target bacteria and fungi. Neutrophils are the most plentiful white cell found in the blood. They usually respond and multiply very quickly, resulting in high white cell counts.

The third major group of white cells are eosinophils, which target larger parasites, such as worms. Eosinophils also moderate allergy inflammation responses.

The fourth major group of white cells, are the lymphocyctes, which work the front lines to identify and destroy foreign invaders. In this group there are three primary types of cells: B-cells, T-cells and natural killer cells. 75% of lymphocytes are T-cells, 10% are B-cells and 15% are natural killer cells. B-cells circulate on the front line in our blood and lymph systems as well as in the tissues throughout the body. They primarily function to identify foreign invaders. B-cells are associated with antibodies, which we'll learn more about in coming videos.

T-cells are white cells that mature in the thymus (part of the lymph system) and then migrate to the point of invasion when called into action. T-cells help surround, bind to and then kill off the invading cells. T-cells also provide an essential regulatory function to ensure that the immune system is not over reacting or under reacting to a pathogen.

Monocytes are unique in that they are partially differentiated white cells, meaning they are not fully mature. They are stored in the lymph system, circulate in the blood and migrate to tissues throughout the body, where they mature into one of two types of cells: macrophages or dendritic white cells. Macrophages ingest and break down both invading microbes as well as infected human cells. Dendritic white cells act like messengers taking the broken down antigen material and presenting it to other white cells, typically B-cells, which will identify the antigen and then trigger a chain reaction that helps activate T-cells.

Monocyctes are also involved in the production of cytokine protein molecules, which carry signals between cells. There are many types of cytokines. One example tied to monocytes is histamine, which leads to an inflammatory response to an antigen. In coming videos we'll get to see more about how these white cells work together.