Download Immune System:

Lec 6
Nov.2016
Immune System
Immunity: is defined as the ability of human body to resist against
harmful chemicals such as toxins that released by microorganism which
tend to damage the tissues & organs. Lymphocytes are key constituents of
the immune system. The lymphatic system includes lymphocytes, lymph
nodes, tonsils, spleen, thymus gland, lymph and lymphatic vessels.
Lymphatic system plays an important role in protecting us against
invading microorganism and other harmful substances
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Types:
1. Innate immunity.
2. Acquired (adaptive) immunity.
A. Innate immunity: in this type of immunity the body is born with the
ability to recognize and destroy certain substances but
cannot
distinguish among different kinds of bacteria and remember previous
encounters. Its components are: 1.mechaical mechanisms. 2. Chemical
mediators. 3. Cells 4. Inflammation.
1. Mechanical mechanisms: such as skin and mucous membranes form
barriers that prevent the entry of chemicals and microorganisms into the
tissues of the body. For example, substances are washed from the eyes by
the tears, from the mouth by saliva, and from the urinary tract by urine.
2. Chemical mediators: a. acid secretion such as HCL in the stomach
and sebum in skin that kill and prevent microbial growths. b.lysozymes in
tears, saliva, nasal secretions and sweat that lyses cells. c. histamine
prostaglandins, complements and leukotriens that promote inflammation
by attracting leukocytes and stimulating phagocytes. d. the other chemical
mediator is pyrogens released by neurophils and monocytes that stimulate
fever production, which inhibit microorganism growth.
3. Cells: such as neutrophils, basophiles, esohophils, mast cells,
monocytes and natural killer cells (are a type of lymphocytes) which are
involved in phagocytosis and production of chemicals that participate in
the response of immune system.
4.Inflammation: when the tissue injury occurs either by bacteria or
chemical there is a release of chemical mediators (also called
chemotaxins or chemotactic factors ) from infected area which attract
leukocytes especially neutrophils to the infected area.. The process of
attraction is called chemotaxis. The leukocyte leaves the walls of
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capillaries to the infected area by a process called diapedesis. The
chemotaxins produce several effects: 1. Vasodilatation. 2. Increased
vascular permeability resulting in edema 3.large amount of fibrinogen
enter into interstitial space from blood and converted into fibrin (clot)
which prevents the spread of infection by ''walling off” the infected area.
The “walling off” process delays the spread of bacteria or toxic products.
The process of killing bacteria continues by neutrophils, and
macrophages until all bacteria or foreign substances are destroyed. The
process of ingestion and digestion of foreign microorganism by
macrophages is called phagocytosis.
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Types of inflammation:
a. localized: which is confined to a specific area of the body. b. systemic:
this occurs in many areas of the body. So one of the results of
inflammation is to “wall off” the area of injury from remaining tissues.
Signs and symptoms of inflammation: are heat, redness, , swelling,
pain ,loss of function, and release of chemicals called pyrogens from
leukocytes which cause fever and inhibit growth of microorganism.
Pus formation: are dead neutrophils, necrotic tissue, and dead
macrophages and tissue fluid. A localized collection of pus is called
abscess.
B. Acquired or adaptive immunity: can recognize and remember a
particular substance. Vaccination is an example of acquired immunity
e.g. typhoid fever, measles, tetanus. Substances that activate adaptive
immunity are antigens which are large molecules with a molecular
weight of 10000 or more for example penicillin. Antigens are proteins or
large polysaccharides. There are two types of antigens:
a. foreign antigens: are not produced by the body but are introduced
from outside it. Pollen, food, drugs and dried skin are foreign antigens
that cause allergic reaction. Transplanted organs and tissues that contain
foreign antigens result in the rejection of the transplant organs. b.Selfantigens: that produced by the body itself. There are two types of
acquired immunity:
1. Humoral immunity.
2. Cellular immunity.
Humoral immunity: is mediated by B-lymphocytes which are produce
plasma
cells. Plasma
cells
produce
circulating
antibodies
or
immunoglobulins (Ig's). Exposure of the body to an antigen from outside
the body, for example bacteria or toxins, can lead to activation of plasma
cells and formation of antibodies which are responsible for destruction of
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antigen. Humoral immunity is a major defense against bacterial
infections.
Humoral
immunity
can
also
cause
immediate
hypersensitivity reactions such as bronchial asthma.
Cellular Immunity: is mediated by T-lymphocytes. It is responsible for
delayed allergic reactions (such as eczema) and rejection of transplants of
foreign tissue. The cytotoxic T cells destroy cells that have the antigen
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which activated them. One mechanism by which they kill is insertion of
pore-forming molecules (perforins) in the membranes of their target cells
which leads to destruction of the cells by osmotic lyses.
Immune system problems of clinical significance:
Hypersensitivity
(allergy): is an undesirable side effect of
immunity. It is defined as an inappropriate activation of the body’s
immune system which may result in a very strong inflammation and
tissue damage. Types of hypersensitivity:
1. Immediate hypersensitivity: This is caused by B-cell immunity.
There is reaction between antibodies and antigens. The symptoms
appears within a few minutes of exposure to foreign antigen. For
example, bronchial asthma, food allergies, hays fever.
2. Delayed hypersensitivity: mediated by T-lymphocytes and
symptoms take several hours or days to develop. Examples, poison
oak, eczema, soaps, measles, cosmetics, & drugs.
Q: write short notes on the allergies in the
allergic person. Give examples
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