Now we'll talk about the white blood cells, these are our leukocytes.
These are nucleated independently modal structures.
They are highly differentiated and these are our cells of the immune system.
They compose the body's defense mechanisms.
They're generated in the bone marrow and normal values range between 4,000 and 11,000 (cells/mm3).
Leukopenia is a term we use to describe a low white blood cell count.
And leukocytosis describes a high white blood cell count.
There are three types: we have the granulocytes, the lymphocytes and the monocytes. We'll touch on each.
First the granulocytes. These are the most numerous.
The nucleus is gonna contain granules and this is where they get their name,
and these are the mediators of our inflammatory response.
Basophils are the least common of these granulocytes and they can perform phagocytosis.
They can produce histamine and serotonin and these cells play a role in immune regulation and allergic responses.
Next we see eosinophils and these make up about 1 to 4% of the white blood cells
and these play a role in the defense against parasitic infections.
These will increase called eosinophilia in the setting of parasites, asthma and certain tropical diseases.
So you can remember, "worms, wheezes and weird diseases" - we will see elevated eosinophils.
Our third is neutrophils and these can perform phagocytosis and are the most abundant type of granulocyte.
Now we'll cover the lymphocytes.
These are the immune response to a foreign substance in the body.
These are found in the lymph nodes, the spleen, the thymus, the tonsils and the lymphoid tissue of the GI tract.
They're going to enter the circulation freely through the thoracic lymph duct.
These can live a long time, up to 1 year.
These are part of the acquired or smart immune system, they have a memory.
There are three types, first the natural killer cells.
These are going to distinguish infected cells and tumors from normal uninfected cells
by recognizing changes in a surface molecule called the MHC.
These become activated and release cytotoxic or cell-killing granules and then they destroy these altered cells.
Next are the B cells.
These are part of the humoral immunity and they're responsible for making large quantities of antibodies
which can neutralize foreign objects like bacteria and viruses.
Last are the T-cells.
These are part of the cell-mediated immune response and these are going to directly attack antigens.
Lymphocytes are expressed as a percentage of the lymphocytes compared to the total number of white blood cells counted.
Lymphocytosis refers to an increased number, and usually this happens in the setting of a viral infection
or in certain kinds of blood cancers or lymphoma.
Lymphocytopenia refers to a decreased number, and we see this in patients with HIV
because this will destroy their T-cells.
Next, the monocytes.
Monocytes are the largest cells of the blood, they compose about 7% of the leukocytes.
They're phagocytic which means they ingest infectious agents and red blood cells.
They're found at the sites of chronic infection and these are made in the bone marrow
and then they're gonna circulate around in the blood.
These are young and they're going to eventually develop into macrophages.
Here you see the timeline.
When they come out, they're just a monoblast, then they mature into a promonocyte
into a monocyte which will further differentiate into a macrophage.
Next are the platelets.
These do not reproduce, these are small fragments of bone marrow cells.
Normal values range from about 150,000 to 400,000 and these are used for clotting.
They also are used to promote other clotting factors in the clotting cascades and these secrete vasoconstrictors.
Platelets attract neutrophils and monocytes to a site of inflammation.
They're also responsible for dissolving clots when they're no longer needed and they can digest and destroy bacteria.
They're also going to secrete growth factors to maintain the lining of the vessels.