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Immunity
L.Saba Abood
Immunity
Immunity is the body's ability to fight off pathogens harmful (micro-organisms),
malfunctioning cells, and foreign particles that invade it.
It is the resistance to infection usually associated with presence of antibodies or cells
that can deactivate pathogens.
Fungi, protozoans, bacteria, and viruses are all potential pathogens
Lymphatic system: its include the lymphatic vessel and lymphatic organs. The
lymphatic organs (red bone marrow, thymus, lymph node and spleen) are responsible
for immune cell production.
Immune system
The Immune System is a system of many biological structures and processes within an
organism that protects against disease. Its produces antibodies or cells that can
deactivate pathogens.
The
immune
system
can
be
classified
innate immune system and the adaptive immune system
into
subsystems:
Lines of defenses in the body
Innate defenses: They are barriers that prevent pathogens from entering the body
and mechanisms able to deal with minor invasions.
– “possessed at birth, as an essential characteristic”
– Always present
– react immediately after contact with pathogen
– are not enhanced upon repeated contact with pathogen (no memory)
– first line of defense
Components of innate defenses
1. Barriers to entry (skin and mucosal membranes)
2. Cells : Phagocytic WBCs (neutrophils and macrophages)
3. Protective proteins are also part of this line of defenses
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Immunity
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The First Line of defense
The body's first line of defense against pathogens uses mostly physical and chemical
barriers such as:
1. Skin: The intact skin is generally an effective physical barrier that prevents
infection. The chemical barrier of the skin is the secretions of sebaceous glands (oil)
which contain chemical that weaken or kill bacteria on the skin.
2. Mucus and Cilia: As you breathe in, foreign particles and bacteria bump into
mucus throughout your respiratory system and become stuck, hair-like structures
called cilia sweep this mucus into the throat for coughing or swallowing.
3. Saliva: contains an antibacterial enzyme called lysozyme that break down
bacteria.
4. Stomach Acid: Swallowed bacteria are broken down by incredibly strong acids in
the stomach that break down your food.
The Second line of defense:
If a pathogen is able to get past the body's first line of defense and an infection starts,
the body can rely on its second line of defense. This will result in what is called an
inflammatory response.
Steps of inflammatory response:
1. Injured tissue cells and mast cell release histamine which causes capillaries to
dilate and increase blood flow.
2. Macrophages phagocytize pathogens and release cytokines which stimulate the
inflammatory response
3. Neutrophils and monocytes (become
macrophages) squeeze through the
capillaries wall and phagocytize pathogens
** if neutrophils die off in great quantities they become a yellow-white substance called
pus.
4. Blood clotting walls off capillary and prevents blood loss.
Signs of Inflammatory Response
•
Redness - due to capillary dilation resulting in increased blood flow
•
Heat - temperature rises
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Swelling – due to passage of plasma from the blood stream into the damaged
tissue
•
Pain – due mainly to tissue destruction and, to a lesser extent, swelling.
when the injury is not serious the inflammatory response is short-lived and healing
process will quickly return the affected area to normal state.
If the neutrophils are overwhelmed, they call for reinforcements by secreting chemical
mediators called cytokines which attract more WBCs to the area including monocytes.
Inflammation is the body's natural response to an irritation or injury , and serves
an important role. once the healing begun, inflammation rapidly subsides.
Protective protein (The complement system)
is composed of a number of blood plasma proteins. which can bind to mast cells
and trigger the histamine release other can attract phagocytes to the scene.
Interferons are proteins produced by virus-infected cells as a warning to noninfected cells in the area. Interferon binds to receptors on non-infected cells
causing them to prepare for possible attack.
Interferons are used as a treatment in some viral infections such as hepatitis C.
Adaptive immune system:
Third line of defense
When innate defenses have failed to prevent an infection, the pathogen is then
heading for the body's last line of defense, the acquired defenses come into play.
Acquired immunity respond to large molecules, normally protein structures,
called antigens(pathogens: for example bacteria, viruses, molds, or parasites all
are antigens.) that the immune system recognizes, attacks, destroys, and
remembers each pathogen that enters the body. For each type of pathogen, the
immune system produces cells that are specific for that particular pathogen.
Unlike the first line and second line defense the immune system
differentiates among pathogens.
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Immunity
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The two main types of acquired immunity are active and passive.
I.
Active Immunity:
lasts for years, the body produce the antibodies which has been exposed to the
antigen in the past either through exposure naturally to the actual disease causing
antigen or artificially by stimulation (vaccination) of immune defenses.
II.
Passive Immunity:
short duration, the body doesn't produce the antibodies. these antibodies are
produced by another source and given to person either naturally by placental
transfer (A mother will pass immunities on to her baby during pregnancy, These
antibodies will protect the baby for a short period of time following birth while its
immune system develops) , or artificially by injection of antibodies.
Acquired defenses depend on the action of lymphocytes, which differentiate
as either B cells or T cell (table)
Cell
Function
B cell
Produce plasma cell and memory cell
Plasma cells
Memory cell
cytotoxic T cells
Produce specific antibodies
Ready to produce antibodies in the future
Regulate immune response; produce cytotoxic T
cells and helper T cell
Kill virus-infected cells and cancer cells
helper T cell
Regulate immunity
Memory T cell
Ready to kill in the future
T cells
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