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.