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Summary Unit 12 D Diseases and infection- BTEC Extended diploma applied medical science
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- PEARSON (PEARSON)
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Unit 12DP5. Explain the components of the specific and the non specific defences, in protecting
the body.
Nonspecific defence is a type of immunity which works to protect the body against invading
pathogens.There are two lines of defence for the nonspecific immune system;
The first line of defence consists of physical barriers which prevent pathogens from entering
the body. These barriers are;
● The skin - This prevents the entry of pathogens by surrounding the whole body and
produces an oily substance called sebum, which also inhibits pathogen growth. The skin
also has a large population of natural healthy bacteria (known as skin flora), which
outcompetes pathogens for surface space.
● Mucous membranes - Surfaces involved in gas exchange, such as the trachea, contain
goblet cells which secretes and forms a layer of mucus which traps pathogens and
contains the enzyme lysozyme which destroys the cell walls of bacteria by digesting the
peptidoglycan.
● Cilla - These are tiny hairs line the surfaces involved in gas exchange/respiration and
work by sweeping the mucus secreted away from the lungs, preventing foreign particles/
pathogens from causing infection.
● Stomach acid - This contains an acidic pH of between 1.5 to 3.5 which works to kill
germs which have entered from the ears/nose/mouth.
The second line of defence consists of barriers which serve as a backup response against
invading pathogens. These barriers are;
● Inflammatory response - This causes swelling of the skin surrounding the rupture and is
characterised by pain, heat, redness and swelling. When the skin is ruptured, mast cells
become activated and release a substance called histamines and cytokines. The
histamines will make blood vessels dilate, bringing more white blood cells to the area
where there is an infection/pathogen, in turn causing localised heat and redness. The
high temperature prevents the pathogen from reproducing.
● Fever - The normal core temperature for humans is 37 degrees, however, during an
infection large white blood cells cause the hypothalamus in the brain (which controls
body temperature) to reset, increasing the temperature. This prevents pathogens from
reproducing as quickly because the body temperature is above optimum temperature/ 37
degrees, allowing the immune system to work faster against the pathogens.
● Blood clotting - If an individual’s skin becomes broken or ruptured, pathogens are easily
able to enter the blood. The blood in a person's body clots to help repair the wound,
prevent bleeding out and prevent pathogens from trying to enter the affected area. It
works by firstly having platelets rush to the affected site and release thromboplastin and
serotonin. The serotonin causes muscles to contract around the wound area, closing the
gap. A hard scab forms as a result of the clot from drying out, which in turn keeps
pathogens from entering the wound. The epidemical (skin) cells grown from underneath
the scab, with collagen fibres reinforcing the skin cells.
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