(4) Communicable Diseases Flashcards
Communicable diseases
Caused by infective organisms - pathogens.
Can be passed between people or species.
Vectors carry pathogens from one organism to another.
Different types of pathogen that can cause disease in plants and animals
Bacteria - tuberculosis (humans and cattle), bacterial meningitis (humans), ring rot (tomatoes and potatoes)
Virus - HIV/AIDS (humans), influenza (animals), tobacco mosaic virus (plants)
Protists - malaria (animals), potato/tomato late blight (potatoes and tomatoes)
Fungi - ringworm (cattle), athletes foot (humans), black sigatoka (banana plants)
Transmission of communicable pathogens
Direct - disease is transmitted directly from one pathogen to another.
Droplet infection (coughing/sneezing).
Sexual intercourse - HIV
Touch - athletes foot.
Indirect - disease is transmitted from organism to another by something else, such as air, water, food or another organism (vector)
Spores carried between plants in the air, then in the water - potato/tomato late blight.
Vectors - malaria
Living conditions - overcrowding increases the transmission of many communicable diseases.
TB - spread directly from droplet infection, and indirectly because bacteria can remain in the air for long periods of time, increase in infection in overcrowded areas.
Climate - malaria is most common in tropical countries because humid conditions are ideal for mosquitos to breed.
Social factors - risk of HIV infection is high when there is limited access to good healthcare, or good health education.
Plant defences
Physical - leaves and stem have a waxy cuticle, prevents water collecting on the leaves, reducing risk of water borne infection.
Cellulose cell wall.
Produce polysaccharide callose which is deposited between plant cell wall and plasma membrane during stress, so it is harder for a pathogen to enter cells. Deposition at plasmodesmata limits the spread of virus between cells.
Chemical - Anti microbial chemicals to kill pathogens and inhibit growth (saponins destroy cell membrane of fungi and other pathogens, phytoalexins inhibit growth of fungi and other pathogens).
Secrete chemicals toxic to insects to decrease transmission of pathogens caused by insects feeding.
Primary, non-specific defences in animals
Same response each time
Physical - skin, mucous membrane, blood clotting.
Inflammation - swelling, pain, heat and redness. Helps to isolate pathogens they have have entered damaged tissue. Vasodilation to increase the blood flow to the area, brings wbcs to the area to fight off pathogens.
Wound repair - skin can repair itself and reform the barrier against pathogen entry. Outer layer = mitosis, tissue below the wound = collagen.
Expulsive reflexes - coughing or sneezing to expel pathogens from the body.
Phagocytosis
Non specific. Triggered by antigens (molecules found on surface of cells), when a pathogen enters the body antigens on its surface are identified as foreign, which activates the immune system.
A phagocyte (white blood cell) carries out phagocytosis.
It recognises antigens on pathogen. Cytoplasm moves around pathogen to engulf it, made easier by opsonins that attach to foreign antigens and aid phagocytosis. Pathogen is contained in a phagosome (vesicle) in the cytoplasm. Lysosome fuses with the phagosome to break down the pathogen, then the phagocyte presents the pathogens antigens - stuck on surface to active other immune system cells (antigen presenting cell)
Neutrophils are the most common phagocyte, they are released in large numbers during infection.
Specific immune response.
An immune response is a response to an antigen which involves lymphocytes and the production of antibodies.
Cell mediated response - T cells (mature in thymus gland)
Humoral response - B cells (mature in bone marrow)
Cell mediated response
APC which has antigens from the pathogen from phagocytosis.
T helper cell has specific, complementary receptor to antigen on APC - clonal selection.
Undergoes clonal expansion by mitosis to produce:
more T helper cells to identify antigen - produce interleukins (cytokines) to help stimulate action of B cells and other types of T cells and macrophages to inject pathogens with Ab-Ag complexes,
T killer cells - kill body cells infected by virus,
T memory cells - immunological memory, recognise other pathogens entering the body later that carries the same antigen, then divide rapidly into T killer cells,
T regulatory cells - suppress the immune system and prevent autoimmune responses.
Humoral response
APC which has antigens from the pathogen from phagocytosis.
T helper cell has specific, complementary receptor to antigen on APC - clonal selection.
Releases interleukin/cytokine which trigger B cells to undergo clonal expansion by mitosis to produce:
B memory cells - immunological memory against pathogen and recognise antigen from previous pathogen, allowing a rapid response to occur if they contact again,
plasma cells - make antibodies which fight off infection.
Structure of antibodies
Glycoproteins called immunoglobulins which bind to specific antigen on the pathogen that has caused the immune response.
Made by 2 heavy polypeptide chains and 2 light polypeptide chains. Held together by disulphide bridges
Top = variable region, different on different antibodies. Antigens bind here.
Bottom = constant region.
Hinge region gives the antibody flexibility allowing it to bind 2 separate antigens.
Function of antibodies
Antibody of antibody-antigen complex acts as an opsonin - complex is easily engulfed and digested by pathogens.
Act as agglutinins - causing pathogens carrying antibody-antigen complexes to clump together, as antibodies can bind to 2 antigens at once, prevents them spreading through the body and easier to engulf.
Neutralising toxins - binds to the toxins produced by pathogens, making them harmless.
Primary and secondary immune responses
When a pathogen enters the body for the first time, antigens on its surface activate the immune response - primary response. This is slow because there isn’t many B lymphocytes that can make the antibody needed. Eventually the body will produce enough to overcome the infection, but infected person will show symptoms. After being exposed to antigen, T and B lymphocytes produce memory cells - memory T lymphocytes remember specific antigen and will recognise it again, memory B lymphocytes record the specific antibodies needed to bind to the antigen. The person is now immune.
If the same pathogen enters the body again, the immune system will produce a quicker response - secondary response. Clonal selection happens faster, memory B lymphocytes are activated and divide into plasma cells that produce the right antibody. Memory T lymphocytes are activated and divide into the correct type of T cell to kill the cell. Kills the pathogen before symptoms start to show.
Blood smears
Stains added to make cells easier to see.
Red blood cells (erythrocyte) - no nucleus.
Neutrophil - multi lobed nucleus and the cytoplasm is grainy.
Lymphocyte - smaller then neutrophil and nucleus takes up most of the cell.
Monocyte - biggest white blood cell, unilobular nucleus and non grainy cytoplasm.
Types of immunity
Natural active - achieved through the primary immune response, the body’s own response to a pathogen.
Natural passive - lats until the immune system of a baby begins to make its own antibodies. Mother passes antibodies to baby through milk.
Artificial active - injection of modified antigens (vaccination) so the body is stimulated to make its own antibodies.
Artificial passive - provides temporary immunity. Antibodies are formed in one individual, then extracted and injected into someone else.
Autoimmune diseases
The body does not recognise the antigens on its own body cells and starts to attack them.
Rheumatoid arthritis - affects the joints, there is no cure but people can take anti inflammatory drugs or steroid.
Lupus - affects skin and joints and causes fatigue, can attack any organ, there is no cure but people can take anti inflammatory drugs or steroids.
