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 ( Immunity
Immunity(resistance):is the body's defense against infectious organisms
and other invaders, through a series of steps called the immune response.
On other words, the ability of an organism to resist infectious disease, it’s
the sum of all naturally occurring defense mechanisms that protect
humans from diseases. The immune system, which is made up of special
cells, proteins, tissues, and organs, defends people against invaders
, keeping people healthy and preventing infections.
There are two types of resistance
1-Non-specific (innate)
2-Specific (acquired)
Non-specific immunity, as the name suggests, is not specific to a certain
group of micro-organisms. These defense mechanisms act against each
and every invader of the body.
Anatomical barriers include physical, chemical and biological barriers.
Skin is the first barrier and the first mechanism of non-specific defense.
The epithelial surfaces form a physical barrier that is impermeable to
most infectious agents, acting as the first line of defense against invading
organisms.
Desquamation of skin epithelium also helps remove bacteria and other
infectious agents that have adhered to the epithelial surfaces. presence of
sebaceous glands in the dermis provides an environment unsuitable for
the survival of microbes. presence of sweat glands that secrete sweat
which washes infections off(High salt content of sweat dries microorganisms off)
The flushing action of tears and saliva helps prevent infection of the
eyes and mouth. Saliva contains anti-bacterial properties due to
lysozymes.
In the gastrointestinal and respiratory tract, movement due to peristalsis
or cilia, respectively, helps remove infectious agents. Also, mucus traps
infectious agents. The gut flora can prevent the colonization of
pathogenic bacteria by secreting toxic substances or by competing with
2
pathogenic bacteria for nutrients or attachment to cell surfaces. Some
epithelia produce mucus which also acts as a barrier against infections. If
micro-organisms penetrate these defense systems they meet the second
line of defense including phagocytic white blood cells , antimicrobial
proteins and inflammatory response
Specific immunity (Adaptive Immunity) : immunity that an organism
develops during lifetime result of exposure to antigens(microbes, toxin or
other foreign substances) it’s the second line of defense involves
production of antibodies and generation specialized lymphocytes against
specific antigens. Specific immune response occurs in two separate
occasions:
1- Naturally acquired immunity
2- Artificially acquired immunity
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