Cell Recognition and the Immune System Flashcards
immunity - how the body deals with disease
what is a communicable diseases
Communicable diseases are diseases which can be spread between organisms either of the same species of sometimes between different species
What are communicable diseases spread by
Communicable diseases are spread by pathogens
What is a pathogen
A pathogen is a microorganism which can cause a disease
What does ‘host’ mean
The organism which the pathogen infects is called the host
state the four main categories of pathogens
Four main categories of pathogens are bacteria, viruses, fungi and Protoctista - also called Protista
describe how bacteria can act as pathogens
bacteria are prokaryotic cells (bacterial chromosomes)
Once they enter the body, pathogenic bacteria can release toxins
Toxin are chemicals which damage host cells and tissues leading to the symptoms of the disease
Some bacteria can enter host cells and prevent them from functioning normally e.g. the bacteria which cause tuberculosis
describe how bacteria can act as pathogens
Viruses prevent a host cell from functioning normally. In many cases a virus can lead to the death of the host cell
Viruses cannot reproduce outside of a host cell
To reproduce, a virus attaches to the host cell and then passes through the cell membrane
The virus then copies itself using the enzymes of the host cell
The virus particles now leave the host cell and can go on to infect new host cells and continue reproducing
Viruses consist of genetic material which can be DNA or RNA
The genetic material is wrapped in a protein structure called a capsid
Viruses also have attachment proteins which allow the virus to attach to host cells
Some viruses also contain a lipid envelope
describe how fungi can act as pathogens
Fungi are eukaryotic organisms - can be unicellular or multicellular
Fungi obtain nutrients by releasing enzymes and digesting the material around them
The products of digestion are then absorbed back into the fungal cells
This process of digestion can cause damage to host cells and tissues
When they reproduce fungi release a large number of spores so fungal diseases can spread very widely
many species of fungi are found on the remains of dead organsims where they take part in the decay process
However pathogenic fungi are found on living organisms where they cause disease e.g. in humans thrush and athletes foot
fungi in plants - damages leaves, reduces rate of photosynthesis - severely reduce the yield of plant crops
how can protoctista (or protista) act as pathogens
Protoctista (or protista) are eukaryotic organisms
Protoctista can act as pathogenic parasites in humans
Describe the body’s non-specific defences against pathogens - SKIN
Skin - provides a protective layer for the majority of the body surfaces
The skin has many layers of cells, including a surface layer of dead cells. This makes the skin difficult for pathogens to penetrate
The surface of the skin is covered with oil sebum produced by sebaceous glands
This forms a slightly acidic layer which can prevent the growth of harmful bacteria.
Healthy skin is also covered with harmless microorganisms which reduce the growth of pathogens by competing for resources
features of non-specific defences
the non-specific defences are the same for all pathogens (unlike specific immune system)
non-specific defences are rapid and prevent pathogens from gaining access to the body
Describe the body’s non-specific defences against pathogens - Lining of trachea and stomach
mucous membranes
Pathogens can enter the body via openings for example the breathing and digestive systems
These (e.g. trachea in breathing system) are lined with a protective layer called a mucous membrane.
Mucous membranes secrete mucus which traps microorganisms
These microorganisms can then be destroyed by white blood cells called phagocytes
The mucus also contains the enzyme lysozyme which destroys bacteria by digesting the bacterial cell wall
In the stomach, the mucus contains hydrochloric acid. This hydrochloric acid helps to kill any pathogens in food or water
Describe the body’s non-specific defences against pathogens - expulsive reflexes
Sometimes pathogens can invade the body through opening such as the mouth or nose
In this case, the body tries to expel the pathogen. These are called expulsive reflexes. These can include sneezing, coughing, vomiting or diarrhoea
Describe the body’s non-specific defences against pathogens - tears
lysozyme is also found in tears where it helps to prevent pathogens from entering via the eyes
Describe the body’s non-specific defences against pathogens - blood clotting
Another way that pathogens can enter is if the skin is damages e.g. a cut
In this case, the body responds to try to seal the damaged area before a large number of pathogens can enter
This is the process of blood clotting involving platelets in the blood
what are the two categories of white blood cells
The two categories of white blood cells are phagocytes and lymphocytes
state a type of phagocyte
Phagocytes include macrophages and neutrophiles
what type of white blood cells form part of the non-specific defences
Phagocytes form part of the non-specific defences
macrophages also play a role in the specific immune system
State examples/types of lymphocytes
Lymphocytes include B lymphocytes and T lymphocytes
what type of white blood cells form the specific immune system
Lymphocytes form the specific immune system
describe the roles of neutrophils and macrophages
neutrophils can rapidly engulf and destroy pathogens at the site of an infection
Macrophages can also destroy pathogens by phagocytosis but macrophages also have an additional function called antigen presentation
describe the stages of phagocytosis
phagocytes are attracted to molecules/chemicals produced by the pathogens
phagocytes have several receptors on their cell-surface membrane that recognise, and attach to , chemicals on the surface of the pathogen and engulf it
the pathogens are contained in a phagocytic vacuole/vesicle called a phagosome
now lysosomes move towards the phagosome and fuse with it, forming a phagolysosome
Lysosomal enzymes (lysozymes) destroy ingested bacteria by hydrolysis of their cell wall/
now break down the pathogen and destroy it
the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
the phagocyte then presents the pathogens antigens - it sticks the antigens on its surface to activate other immune system cells/lymphocytes - macrophages
what does the specific immune system include
Antibodies
Lymphocytes (B and T)
What does the specific immune system do
The specific immune system responds to each pathogen in an individual way
Once the specific immune system has defended against the pathogen, it will then produce a more effective response if it encounters the same pathogen again
Key feature - it can recognise individual pathogens
describe what is meant by an antigen
Molecules (such as proteins and polysaccharides) which cover the surface of all cells
These molecules often carry out normal cellular functions - called antigens
what leads to an immune response
The immune system can detect antigens on the surface of pathogens
The immune system can see these antigens as foreign or ‘non-self’
This leads to an immune response
describe what happens during an immune response
During an immune response, antibodies will be produced which specifically bind to the antigen
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pathogen
‘non-self’ antigen
antibody
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antibodies are specific
Explain why the antigens on your body cells do not trigger an immune response
Antigens on the surface of your body cells do not trigger an immune response
That is because your immune system identify these antigens as ‘self’ - a normal part of your body
The immune system does not produce antibodies against self antigens
what are antibodies also referred to as
Antibodies are also referred to as immunoglobulins
describe what is meant by an antibody
Antibodies are glycoproteins consisting of four polypeptide chains
describe the structure of antibodies
Antibodies are glycoproteins consisting of four polypeptide chains
It has two long heavy chains, which are identical to each other, and it has two shorter light chains which are also identical to each other
The chains are held together by disulphide bridges
It also has two antigen binding sites
This means that one antibody molecule can bind to two identical antigen molecules
When antigens bind, it is called an antigen-antibody complex
The tertiary structure of the antigen-binding site is complementary to the structure of the antigen (the antigen fits perfectly into the antigen-binding site)
This means that antibodies are highly specific for the antigen they bind to
The hinge region (bend) is flexible allowing the distance between the two antigen binding sites to vary
draw an antibody
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What are antibodies produced by
Antibodies are produced by B lymphocytes
describe the roles of antibodies in the specific immune system
The role of antibodies in the immune system is referred to as humoral immunity
explain the similarities differences between antibodies from two different B lymphocytes
Both antibodies have a region which is the same. This is called the constant region.
The constant region has the same structure for every antibody no matter which B lymphocyte produced it
However, the ends of the antibody molecules are different. These are called the variable regions. These are about 110 amino acids long on each chain
The variable regions form the antigen-binding sites
The shape of the variable regions are different for the antibodies produced by different B lymphocytes
This means that the antibodies produced by different B lymphocytes will bind to different antigens
human body contains millions of different B lymphocytes so there are millions of different antibodies targeting a vast range of antigens
functions of antibodies in the human body
Antibodies
act as markers that stimulate phagocytes to engulf the bacterial cells to which they are attached - for phagocytosis
Antibodies can stick pathogens together preventing them from spreading around the body. This makes it easier for phagocytes to locate them as they are less spread-out within the body. This is called agglutination
By sticking to pathogens such as viruses, antibodies prevent them from invading host cells
Antibodies can stick to bacterial toxins preventing the toxins from harming body cells.
These antibodies are called antitoxins
