Download Title: White Blood Cells (Leukocytes, Leucoytes)

Title: White Blood Cells (Leukocytes, Leucoytes) and Platelets
1- Introduction: Unlike red blood cells WBC’s have a nucleus and do not contain
hemoglobin. White blood cells are classified as either granular (containing
granules) or agranular (no granules) These granules are vesicles that contain a
variety of immune related substances. The granular WBC’s are the neutrophils,
eosinophils, and basophils. The agranular WBC’s inclue the lymphocytes and
monocytes.
2- Granular Leukocytes – After staining (H&E) the following three types of WBC’s
have a distinctive coloration easily visible under the microscope
a- Eosinophils
b- Basophils
c- Neutrophils
3- Agranular leukocytes – These WBC’s do contain granules, however do their small
size and poor staining ability they are not visible under a light microscope
a- Lymphocyte
b- Monocyte
4- Functions of White Blood Cells –
a- The skin and mucus membranes are continuously exposed to microscopic
organisms (pathogens), such as bacteria, parasites,..
b- Once a pathogen enters the body the general function of WBC’s is to
destroy these pathogens by phagocytosis or immune response
c- To accomplish this most WB’s leave the blood stream and accumulate at
the site of the pathogen
d- WBC’s exit the capillaries into the tissue in a process called emigration,
they accomplish this with the help of adhesion molecules
e- Materials released by the pathogens attract the white blood cells to the
area of exposure. This process is called chemotaxis
f- Neutrophils respond most quickly to the site of injury or invasion. After
phagocytosis they release lysozyme, hydrogen peroxide and hypochlorite
anion (similar to bleach) to destroy the cellular contents of the invader.
g- Monocytes take longer to get to the scene of the invader but arrive in
much greater numbers. Upon arrival they differentiate into macrophages
which are capable of much greater phagocytosis than neutrophils.
h- Any basophils in the area release histamine, heparin and serotonin. These
substances increase the inflammatory reaction and are involved in
hypersensitivity (allergic reactions)
i- Eosinophils in the area release histaminase which helps to regulate the
effects of histamine and control the reaction
j- Lymphocytes are the most important players in the immune response. The
three main type of lymphocytes are
1- B-Cells which develop into plasma cells which produce antibodies to
various toxins
2- T-Cells which attack viruses, fungi, transplanted cells and cancerous
cells
3- Natural Killer Cells attack a wide variety of infectious microbes and
spontaneously arising tumor cells
5- WBC Life Span – Most WBC live only a few days this is do impart to the fact
that has they fill up with phagocytized material it begins to interfere with the
functions of the cell.
a- WBC usually number between 5,000 and 10,000 cells per L.
Leukocytosis (10,000+ cells) usually indicates an inflammation or
infection. Leukopenia (5000 cells) is never beneficial and is indicative of
shock, radiation or chemotherapy treatment.
b- Differential WBC count – measures the number of each of the 5 WBC’s
types in a sample of 100 WBC’s. Because each WBC plays a different role
it is possible to use this differential to assist in diagnosing a disease.
c- Significance of HIGH or LOW WBC count
WBC type
Neutrophils
High count may indicate
Low count may indicate
Lymphocytes
Monocytes
Eosinophils
Basophils
6- Platelets – Platelets are also known as thrombocytes. Platelets are formed when huge
megakaryocytes formed from myeloid stem cells under the direction of the hormone,
thrombopoietin, splinter into 2,000 – 3,000 fragments in the bone marrow and then enter
the bloodstream. Platelets have no nucleus, they are about 2-4 m in length. There are
about 150,000 – 400,000 platelets per l. Platelets contain chemicals that promote blood
clotting. They live for 5-9 days and are removed from the circulation by macrophages
found in the liver and spleen.