Download White Blood Cells and Blood Clotting Handout 2013

WHITE BLOOD CELLS (WBC) / LEUKOCYTES
White blood cells (WBC) function in the immune system of the body. They spend most of their
time in the tissues. They have a life span that ranges from minutes to years, depending on the
activity in the tissue and the type of WBC. They use the bloodstream to travel from one organ
to another and for rapid transportation to areas of invasion or injury. WBC are able to detect
chemical changes in damaged tissue. This signal triggers the migration from the bloodstream
into the tissue. They are divided into two general groups: granular and agranular leukocytes.
Granular leukocytes are formed in red marrow and contain granules in the cytoplasm. There
are three kinds of granular leukocytes according to the way the granules stain. They are:
1). neutrophils = [stain light purple because some of the granules pick up acid (red) and some
pick up base (blue) stains] – survive minutes to days – These make up most of the
wandering leukocytes & are the first to respond to bacterial infection. They are important
phagocytes.
2). basophils = [stain dark blue in basic stain] – survive minutes to days – These cells give off
histamine and heparin during allergic reactions which increase the inflammatory response
mechanism. They act like the mast cells found in connective tissue.
3). eosinophils = [stain red in acid stain] – survive minutes to days – They can be phagocytic
and they release enzymes that combat the effects of histamine in allergic reactions. They
also defend the body against certain parasitic worms by releasing digestive enzymes on
the surface of the parasite.
Agranular leukocytes also contain granules in the cytoplasm but the granules are not stained
easily and cannot be seen with a light microscope. There are two types:
1). monocytes = survive months or longer – They are formed in the red marrow and migrate to
infection sites in large numbers but take longer to reach the sites than the neutrophils.
They become activated at the infection sites and develop into macrophages which
phagocytize foreign cells and cellular debris.
2). lymphocytes = survive months to years – They form the backbone of the immune system.
They develop in red marrow and also in lymph tissue (tonsils, thymus gland, spleen, lymph
nodes). Some lymphocytes become T lymphocyte cells or T cells, and fight the invasion of
virus infected cells and cancer cells. Other lymphocytes become B lymphocyte cells. B
cells become the plasma cells that produce and secrete antibodies (immunoglobulins) into
the bloodstream. Still other lymphocytes develop into NK (natural killer) cells. They are
nonspecific leukocytes that destroy a variety of infected or cancerous cells before the
immune system can be activated.
BLOOD CLOTTING
The formation of a blood clot is a complex process that required at least fifteen substances.
Two proteins essential to the process are: prothrombin (type of globulin) – the inactive clotting
protein present in plasma and fibrinogen – another protein found in plasma.
Platelets and damaged cells also function in the clotting process. An overview of the process of
clot formation follows:
1. The damaged cells and platelets attach at the wound site, develop extensions and
adhere to collagen fibers that are already present. This "plugs" the wound.
2. The platelets rupture and release two substances: vasoconstrictors, which cause
nearby blood vessels to constrict and reduce blood loss and thromboplastin (enzyme).
3. The presence of thromboplastin + Ca ions (already present) convert the prothrombin to
thrombin. Thrombin is an enzyme that breaks apart the large fibrinogen molecules
forming sticky protein fibers called fibrin.
4. The fibrin fibers + ruptured platelets + red and white blood cells normally present, create
a network which solidifies and forms a clot that stops the bleeding.
5. The clot contracts as it solidifies, pulling the wound together. This prevents further
bleeding and aids in the healing process.
HEMOPHILIA = GENETIC MALFORMATION OF PROTEIN THROMBOPLASTIN
Hemophilia is caused by the absence of thromboplastin (enzyme is incorrectly formed).
This means that step #3 of the above clotting process does not occur.
NOTE: The ability to form clots may also be impaired by a lack of Ca ions or a vitamin K
deficiency. Vitamin K is needed to synthesize prothrombin (occurs in the liver).