Welcome back to my channel, in today’s video we are going to go over the types
of white blood cells and their functions. White blood cells, also known as leukocytes , are
important cells found in the blood and lymphatic system that function as part of the immune system.
White blood cells are made in the bone marrow from multipotent stem cells and move out into
the blood stream and lymphatic system. From these multipotent stem cells you
get two lineages of blood cells; myeloid progenitors and lymphoid progenitors.
The myeloid lineage goes on to form the red blood cells and platelets,
as well as four of the white blood cell types; basophils, neutrophils, eosinophils and monocytes.
The lymphoid lineage goes on to form the lymphocytes.
The neutrophils, eosinphils and basophils are also granulocytes, which means they
contain granules within their cytoplasm. One common feature of all white blood cells
is that they all have a nucleus, which are absent in both red blood cells and platelets.
The first and most common white blood cell we are going to go over is the neutrophil.
Neutrophils make up ~65% of the white blood cells found in the blood.
Neutrophils have a multi-lobed nucleus, which has between 2 and 5 lobes.
These lobes are connected by a chromatin strand. Around the nucleus there is the cytoplasm,
that has many fine granules within. The main function of neutrophils as part of
the immune system is in responding to inflammation and infection caused by bacteria and fungi.
When responding to infections by these pathogens the cell phagocytoses the pathogen.
Once inside the neutrophil the granules release a range of enzymes,
proteases, and defensins that play an important role in killing the pathogen.
The next white blood cell is the eosinophil, also known as an acidophil.
Eosinophils are much less common, only making up around 3% of the white blood cells in the blood.
Eosinophils also have a lobed nucleus, it is usually bi-lobed having only two lobes.
Surrounding the nucleus is the cytoplasm, that also contains granules.
The main function of eosinophils as part of the immune system is
in responding to parasitic infections. Eosinophils are not phagocytic like neutrophils,
instead they release cytotoxic substances that kill the parasite.
They also respond to allergens. The next white blood cell is the basophil.
Basophils are the least common white blood cell making up less than 0.5
% of the white blood cells found in the blood.
Again the nucleus of basophil cells are lobed, usually bi-lobed.
In the cytoplasm there are large coarse granules that often obstruct a clear view of the nucleus.
These granules contain the chemicals histamine and heparin.
The main function of basophils as part of the immune system
is in responding to allergens and antigens. The next white blood cell is the monocyte.
Monocytes are the largest of the white blood cells.
The nucleus is large and kidney shaped and occupies a large portion of the cell.
The cytoplasm does not usually have any granules. The main function of monocytes as part of the
immune system is in phagocytosis. When monocytes move out of the
bloodstream they become macrophages where they move around the body and phagocytose
microbes and other foreign materials. Monocytes can also become dendritic cells.
The last type of white blood cell are the lymphocytes.
Lymphocytes are the second most abundant type of white blood cell making up between 20 and
40% of the white blood cells found in the blood. They are also abundant in the lymphatic system.
They have a central spherical nucleus that takes up almost all of the cell leaving
little or no cytoplasm around it, sometimes the nucleus is also slightly indented.
Lymphocytes usually lack granules in their cytoplasm.
The main function of lymphocytes as part of the immune system is in responding to
specific antigens and having a specific response to this antigen to eliminate it.
There are three main types of lymphocyte cells; T cells, B cells and natural killer cells.
T cells mature in the thymus and their main function is in being part of cell-mediated
immunity, this means their response to pathogens or unhealthy cells does not involve antibodies.
B cells have receptors of the surface of the cell that allow for antigens to bind.
B cells function is in being part of the humoral immunity system, which means their response to
pathogens involves the use of antibodies. Natural killer cells have granules, these
are smaller and less visible than those found in the white blood cells considered granulocytes.
Natural killer cells function in a rapid response in destroying infected or cancerous
cells by releasing cell destroying enzymes from the granules found within the cell.
They also release cytokines which work as signal molecules that activate
macrophages to come and destroy extracellular pathogens.
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