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Unit 12 - Assignment 4
Body Defences
An Introduction to the Assignment
To pathogenic microorganisms, the human body is viewed as a suitable environment with acceptable
temperatures of 37oC, humidity, pH neutrality and nutrients that can all be used to allow for
colonisation, which maintains and benefits their own survival. Parasitic pathogens including viruses
do not require any of these conditions and only require the cells of the host to manipulate the
organelles within them to produce even more individual virions. These pathogens can only achieve
these aims through the process of infection, which involves the internal infiltration of the body.
Naturally, an infection can eventually end up killing the host without interference from any form of
protection and it is because of this that the human body has evolved to counteract any pathogen that
may attempt to colonise the host and their organ tissues. The protection that the body owns are called
defensive mechanisms and they can either be very specific or nonspecific.
Specific and Non-Specific Defence Mechanisms
There are many defence mechanisms that the body utilises to protect itself from harmful
microorganisms, with some basic examples including the Influenza virus and some species of E.coli
bacteria. Some of these defences act as large physical barriers that are impenetrable to small
pathogens due to the components that make up their structure, while others are chemical-based
barriers that provide environments too extreme for most microorganisms to maintain their normal
metabolic processes, which keeps them “alive” (viruses are not considered as live microbes); this can
be a result of being within an environment too acidic or too basic. Physical and chemical barriers are
general defences, meaning they are not used to defeat specific forms of pathogens, but rather aim to
destroy any microorganism that has not already adjusted to the extreme conditions it provides; this is
evident in the form of some other species of microbes that have adapted to acidic or basic
environments and can therefore survive within them, for example Salmonella is a pathogenic bacteria
that infects the intestinal tract and infiltrates the body by ingesting raw meats such as chicken, where
it reaches the intestines by surviving the stomach acid through adaptations of its cell wall and
membrane. These barriers are not always reliable because of instances such as this, however they still
provide an adequate defence against many pathogens.
Because nonspecific defences are not entirely reliable as they do not provide a secure form of
protection against all forms of pathogens, another more flexible defensive mechanism is required to
destroy more specific pathogens that may enter the body. This is known as the specific defensive
mechanisms and this includes a large majority of the immune system; more specifically the entirety of
the adaptive immune system. The white blood cells that deal with recognising the antigens on the
surface of pathogens are referred to as lymphocytes, where they can replicate and form memory cells
that can easily detect the same antigen when it occurs in the future for a more rapid response.
These two defence mechanisms differ because nonspecific defence mechanisms are not capable of
rapidly adapting to infection as these work to initially prevent it from occurring, meanwhile the
specific response usually occurs after an infection has begun as specific responses are typically
delayed, although they are much more effective with the disposal of microorganisms. Furthermore,
nonspecific responses have no individual no targets, whereas each lymphocyte possesses specialised
By Lewis Keyte
, 2
receptors to detect a certain antigen on the surface of a specific pathogen, for example the released
antibodies form B lymphocytes that are used to recognise the surface antigens on the Salmonella
bacteria is called PA1-20811, meaning this type of antibody only binds onto these antigens. Because
nonspecific defences are the least adaptable, these barriers are recognised as being the first line of
defence because they are quicker to respond as a result of lacking any individual or specific targets,
while specific responses differ because they are the second defensive mechanism that are only used
when a pathogen surpasses the first line of defence, where the microbe has infiltrated the bloodstream
or primary organs; an example is malaria, which attacks the liver.
However, it is important for the body to own both of these defence mechanisms because the specific
response is relatively delayed as it takes time for T lymphocytes (more on page …) to obtain antigens
and proliferate into a large number of adapted immune cells that can effectively fight the pathogen
that has caused the infection; this means that the first line of defence can be used to slow down the
rate of infection while more effective cells are being produced. Furthermore, nonspecific defences can
weaken the pathogen or completely be rid of it without the needed intervention of the specific immune
system, this is effective due to the limited number of adapted cells that are within the body at any
given time; the use of these specific cells can leave them fewer in numbers as these immune cells die
from exhaustion shortly after they are stimulated, making the body vulnerable to other infections until
more are produced.
The Non-Specific Defences
Nonspecific defences are the first line of defence that do not target a specific species or class of
pathogen, but rather they focus on destroying microorganisms that cannot withstand one type of
extreme conditions, for example too acidic or too basic conditions. The function of these defence
mechanisms are to prevent the pathogen from gaining a prolonged foothold in the body to prevent
infection and - if allowed to develop - colonisation. There are many types of these defences with three
main forms of nonspecific systems including physical barriers, chemical barriers and phagocytosis.
Physical Barriers - The Skin
The skin is the outermost defensive layer of the body that serves many different functions including
insulation due to the materials that make up the tissues and the thick layers of the organ. Within the
case of infection, the skin acts as a protective physical barrier that shields the internal organ systems
from invasive bacteria and viruses. The epidermis of the skin is the outermost layer that covers the
entirety of the body’s surface and consists of inactive dead cells that no longer possess functional
organelles, which is an effective mechanism because it prevents intracellular parasites such as viruses
from infecting them as they cannot manipulate the organelles to form new virions, meaning this layer
instead acts as an inert, overlaying barrier. While being naturally impenetrable to pathogens, physical
trauma from cuts can form open wounds that break the skin and can temporarily allow
microorganisms to enter the deeper layers of the skin; the dermis layer, which is the thickest layer of
the organ and consists of alive and healthy skin cells.
The maturity of the cells differ with the depth of the dermis layer with the deepest region of the skin
consisting of the newly replicated and therefore youngest skin cells, while the mature and developed
cells being closer to the epidermis; this means that the age of the skin cells can easily be determined
by the distance from the epidermis to the dermis layers. Because these cells are alive, they are
By Lewis Keyte
Unit 12 - Assignment 4
Body Defences
An Introduction to the Assignment
To pathogenic microorganisms, the human body is viewed as a suitable environment with acceptable
temperatures of 37oC, humidity, pH neutrality and nutrients that can all be used to allow for
colonisation, which maintains and benefits their own survival. Parasitic pathogens including viruses
do not require any of these conditions and only require the cells of the host to manipulate the
organelles within them to produce even more individual virions. These pathogens can only achieve
these aims through the process of infection, which involves the internal infiltration of the body.
Naturally, an infection can eventually end up killing the host without interference from any form of
protection and it is because of this that the human body has evolved to counteract any pathogen that
may attempt to colonise the host and their organ tissues. The protection that the body owns are called
defensive mechanisms and they can either be very specific or nonspecific.
Specific and Non-Specific Defence Mechanisms
There are many defence mechanisms that the body utilises to protect itself from harmful
microorganisms, with some basic examples including the Influenza virus and some species of E.coli
bacteria. Some of these defences act as large physical barriers that are impenetrable to small
pathogens due to the components that make up their structure, while others are chemical-based
barriers that provide environments too extreme for most microorganisms to maintain their normal
metabolic processes, which keeps them “alive” (viruses are not considered as live microbes); this can
be a result of being within an environment too acidic or too basic. Physical and chemical barriers are
general defences, meaning they are not used to defeat specific forms of pathogens, but rather aim to
destroy any microorganism that has not already adjusted to the extreme conditions it provides; this is
evident in the form of some other species of microbes that have adapted to acidic or basic
environments and can therefore survive within them, for example Salmonella is a pathogenic bacteria
that infects the intestinal tract and infiltrates the body by ingesting raw meats such as chicken, where
it reaches the intestines by surviving the stomach acid through adaptations of its cell wall and
membrane. These barriers are not always reliable because of instances such as this, however they still
provide an adequate defence against many pathogens.
Because nonspecific defences are not entirely reliable as they do not provide a secure form of
protection against all forms of pathogens, another more flexible defensive mechanism is required to
destroy more specific pathogens that may enter the body. This is known as the specific defensive
mechanisms and this includes a large majority of the immune system; more specifically the entirety of
the adaptive immune system. The white blood cells that deal with recognising the antigens on the
surface of pathogens are referred to as lymphocytes, where they can replicate and form memory cells
that can easily detect the same antigen when it occurs in the future for a more rapid response.
These two defence mechanisms differ because nonspecific defence mechanisms are not capable of
rapidly adapting to infection as these work to initially prevent it from occurring, meanwhile the
specific response usually occurs after an infection has begun as specific responses are typically
delayed, although they are much more effective with the disposal of microorganisms. Furthermore,
nonspecific responses have no individual no targets, whereas each lymphocyte possesses specialised
By Lewis Keyte
, 2
receptors to detect a certain antigen on the surface of a specific pathogen, for example the released
antibodies form B lymphocytes that are used to recognise the surface antigens on the Salmonella
bacteria is called PA1-20811, meaning this type of antibody only binds onto these antigens. Because
nonspecific defences are the least adaptable, these barriers are recognised as being the first line of
defence because they are quicker to respond as a result of lacking any individual or specific targets,
while specific responses differ because they are the second defensive mechanism that are only used
when a pathogen surpasses the first line of defence, where the microbe has infiltrated the bloodstream
or primary organs; an example is malaria, which attacks the liver.
However, it is important for the body to own both of these defence mechanisms because the specific
response is relatively delayed as it takes time for T lymphocytes (more on page …) to obtain antigens
and proliferate into a large number of adapted immune cells that can effectively fight the pathogen
that has caused the infection; this means that the first line of defence can be used to slow down the
rate of infection while more effective cells are being produced. Furthermore, nonspecific defences can
weaken the pathogen or completely be rid of it without the needed intervention of the specific immune
system, this is effective due to the limited number of adapted cells that are within the body at any
given time; the use of these specific cells can leave them fewer in numbers as these immune cells die
from exhaustion shortly after they are stimulated, making the body vulnerable to other infections until
more are produced.
The Non-Specific Defences
Nonspecific defences are the first line of defence that do not target a specific species or class of
pathogen, but rather they focus on destroying microorganisms that cannot withstand one type of
extreme conditions, for example too acidic or too basic conditions. The function of these defence
mechanisms are to prevent the pathogen from gaining a prolonged foothold in the body to prevent
infection and - if allowed to develop - colonisation. There are many types of these defences with three
main forms of nonspecific systems including physical barriers, chemical barriers and phagocytosis.
Physical Barriers - The Skin
The skin is the outermost defensive layer of the body that serves many different functions including
insulation due to the materials that make up the tissues and the thick layers of the organ. Within the
case of infection, the skin acts as a protective physical barrier that shields the internal organ systems
from invasive bacteria and viruses. The epidermis of the skin is the outermost layer that covers the
entirety of the body’s surface and consists of inactive dead cells that no longer possess functional
organelles, which is an effective mechanism because it prevents intracellular parasites such as viruses
from infecting them as they cannot manipulate the organelles to form new virions, meaning this layer
instead acts as an inert, overlaying barrier. While being naturally impenetrable to pathogens, physical
trauma from cuts can form open wounds that break the skin and can temporarily allow
microorganisms to enter the deeper layers of the skin; the dermis layer, which is the thickest layer of
the organ and consists of alive and healthy skin cells.
The maturity of the cells differ with the depth of the dermis layer with the deepest region of the skin
consisting of the newly replicated and therefore youngest skin cells, while the mature and developed
cells being closer to the epidermis; this means that the age of the skin cells can easily be determined
by the distance from the epidermis to the dermis layers. Because these cells are alive, they are
By Lewis Keyte
