4.12 Communicable Diseases Flashcards
What is a communicable disease?
A disease caused by a pathogen
How do pathogens cause harm?
- Damage the tissues - enter cells and destroy them
- Produce toxins - act as inhibitors to enzymes or other processes which use proteins e.g. protein receptors in synapses
Give 3 examples of bacteria
Tuberculosis, Salmonella, Ring rot
Give 3 examples of viruses
HIV/AIDS, Influenza, Tobacco Mosaic Virus
Give 3 examples of fungi
Ring worm, Athlete’s foot, Black Sigatoka
Give an example of a protoctista
Malaria, Potato blight
Define direct transmission in animals
Pathogen is transferred directly from one individual to another
Give 3 examples of direct transmission in animals
- Direct contact - kissing & bodily fluids, skin contact, microorganisms
- Inoculation - through break in skin, animal bite, puncture wound
- Ingestion - contaminated food, licking fingers
Define indirect transmission
Pathogen travels from one individual to another indirectly
Give 3 examples of indirect transmission in animals
- Fomites - inanimate objects e.g. bedding, socks, cosmetics
- Droplet infection - Minute drops of saliva and mucus from speaking/coughing/sneezing
- Vectors - transmits communicable pathogens from one host to another e.g. water mosquitoes, fleas.
Outline factors affecting transmission in animals
- Overcrowded living
- Poor nutrition
- Compromised immune system
- Poor disposal of waste
- Climate change - can introduce new vectors/diseases’
- Culture and infrastructure - certain medical practices can increase transmission
- Socioeconomic factors - lack of trained health workers / public warning when outbreak occurs
Define direct transmission in plants
Infected plant coming into direct contact with another
Give 2 examples of direct transmission in plants
- Soil contamination - infected plants leave pathogens in soil
- Vectors
Give 4 examples of vectors (plants)
- Wind - bacteria, viruses, fungal spores can be carried by wind e.g. Black Sigatoka is blown between Caribbean islands
- Water - spores swim in the surface film of water on leaves; raindrop splashes carry pathogens
- Animals - insects/birds carry pathogens/spores directly from one plant to another; insects such as aphids directly inoculate pathogens into plant tissue.
- Humans - hands, clothing farming practices + transport of crops around the world spread pathogens
Outline factors affecting transmission in plants
- Planting crop varieties susceptible to disease
- Over-crowding increases likelihood of contact
- Poor mineral nutrition reduces resistance of plants
- Damp, warm conditions increases survival and spread of pathogens & spores
- Climate change - increased rainfall and wind promote spread of disease; vectors spread to new areas; drier conditions may reduce spread
What is the non-specific immune system?
- Gives the same response each time the same pathogen attacks
- Does not distinguish between different pathogens
- Present from birth
Detail examples of the non-specific immune system
- Epidermis of skin - dead layers of cells & clotting
- Mucous membranes - protective layer
- Chemicals such as: lysozyme in tears/urine; HCl in stomach
What is the specific immune system?
Involves antibodies and T- and B-Cells
Detail examples of the non-specific immune system
- Epidermis of skin - dead layers of cells & clotting
- Mucous membranes - protective layer
- Chemicals such as: lysozyme in tears/urine; HCl in stomach
What are antigens?
- Proteins/molecules on cell surface
- Generate an immune response
- System can tell difference between self/non-self due to antigens
- Not always a good thing; cancers/transplants
What are phagocytes?
- WBCs
- Continually produced from stem cells on bone marrow
- Stored in bone marrow
- Released into blood to engulf pathogens
Name the two types of phagocytes
Neutrophils and Macrophages
What are neutrophils?
- 60% of WBCs
- Smaller than macrophages and short lived
- Chemotaxic - (Move to chemicals)
- Numbers increase rapidly during infection and move into tissues through leaky capillary walls.
What are macrophages?
- 4%of WBCs
- Phagocytic but play a role in activating the specific immune system
How do macrophages work?
- ## Circulate in blood and tend to remain in organs such as lungs, spleen, lymph nodes and kidneys
How do macrophages work?
- Circulate in blood and tend to remain in organs such as lungs, spleen, lymph nodes and kidneys
- Squeeze through leaky capillary walls
What is opsonisation?
The binding of an antibody to the surface of a pathogen to tag the pathogen so that the phagocyte can identify and engulf it
Some opsonins can make pathogen walls leaky so they swell and burst
What are opsonins?
Proteins released by the liver and phagocytes which circulate the blood in an inactive state. They are activated in the presence of bacteria and yeasts.
Describe the four mechanisms of opsonins
- Deposited on membrane of pathogen and make it porous
- Stimulate histamine release from mast cells
- Attract phagocytes to infection - chemotaxis
- Opsonisation
How do opsonins function?
- One end of the complement protein binds to a molecule on the bacterial membrane
- Other end binds to phagocyte
- As phagocyte binds to complement proteins, the bacterial cell is engulfed
What are mast cells?
Granular cells found in connective tissue when an injury occurs
What do mast cells do?
- Release histamine
- Release cytokines
What does the release of histamine do?
- Relaxes arterioles to increase blood flow
- Makes capillaries more leaky
- Attracts phagocytes
- Makes sensory neurones more sensitive
What are cytokines?
Chemicals which attract phagocytes to the site of the the wound which engulf and digest the pathogens
Describe the action of phagocytosis
- Complement proteins released by liver and phagocytes help the phagocytes recognise pathogen
- Phagocytes engulf bacteria (or other debris)
- Ingested cells are enclosed in a vacuole
- Lysozymes fuse with vacuole and release hydrolytic enzymes into it
- The soluble products are then absorbed
Describe the action of macrophages
- They become Antigen Presenting Cells (APCs)
- They combine the antigens from the pathogen with a glycoprotein from the macrophage Major Histocompatability Complexes (MHC)
- These are positioned on the cell surface membrane to signal to the lymphocytes
What are lymphocytes?
A part of the specific immune response which learns the antigens of the pathogen so that it can respond to it directly next time
How is the cytoskeleton used in phagocytosis?
- Moves the pseudopodia to enable the phagocyte to move
- Moves the lysosomes towards the phagosome
How is ATP used in phagocytosis?
Large numbers of mitochondria provide ATP for endocytosis and exocytosis when excreting waste products
Outline the structure of an antibody
Heavy chain: Contains constant regions and is joined by disulphide bridges
Light chain: Connects to heavy chain via flexible hinge regions; contains specific variable regions connecting to specific antigen
How is an antibody specialised to its function?
- Each antibody contains 2 variable regions to connect to 2 of the same antigen
- Each antibody is complementary to one specific antigen which it can bind to forming an Antigen-Antibody Complex
- Constant regions are all the same so phagocytes can recognise them
What is agglutination?
Formation of clumps of cells by antibodies causing microbes to stick together so that phagocytes can engulf them more easily
What is neutralisation?
Antibodies produce anti-toxins to neutralise toxins released by pathogens
What is clonal selection?
Part of immune response. Process of choosing the correct lymphocyte to fight the infection - occurs during the ‘lag phase’
Outline the process of clonal selection
Activated T-helper cells bind to the B-cell with the correct antibody
Interleukins produced by the T-cell helps activate the B-cell
Outline the process of clonal expansion
The activated B-cell divides via mitosis to give clones of plasma and memory B-cells.
Give 4 types of T-Cell (T-lymphocytes)
- T-helper cells
- T-killer cells
- T-memory cells
- T-regulator cells
What are T-helper cells?
- Produce interleukins ( a type of cytokine (cell signalling molecule))
- Interleukins stimulate activity of B cells
- This then increases antibody production and stimulates production of other T-Cells and stimulates macrophages to engulf pathogens with AA Complexes
What are T-killer cells?
Destroy the pathogen carrying the antigen
Produce a chemical called perforin which makes holes in pathogen membranes
What are T-memory cells?
Live for a long time and divide rapidly to form a large number of T-killer cells when met with an antigen for the 2nd time
What are T-regulator cells?
Supress the immune system to regulate it - they stop the immune response when the pathogen has been eliminated to prevent an autoimmune response
Give 3 types of B-Cells (B-lymphocytes)
- Plasma cells
- B-effector cells
- B-memory cells
What are plasma cells?
Produce antibodies for a specific antigen
What are B-effector cells?
Divide to form plasma cell clones
What are B-memory cells?
Provide immunological memory for a specific antigen for a very long time
Outline the process of clonal expansion
The activated B-cell divides via mitosis to give clones of plasma and memory B-cells.
What is an autoimmune disease?
When the body fails to recognise ‘self’ cells and attacks itself. e.g. Rheumatoid arthritis/type-1 diabetes/lupus
Describe the process of inflammation
- Mast cells are activated in damaged tissue
- They release histamines and cytokines
- Histamines cause blood vessels to dilate causing localised redness/heat
- Histamines make blood vessel walls more leaky so tissue fluid is created
- This causes swelling and pain
- Cytokines attract phagocytes to the site which dispose of pathogens via phagocytosis
Describe the process of cell-mediated immunity
- Macrophages engulf and digest pathogens in non-specific immune system. They process antigens from surface of pathogen to form APCs
- Receptors on T-helper cells fit antigens, they produce interleukins which stimulate more T-cells to divide rapidly by mitosis to form more T-helper cell clones.
- Cloned T-cells may: develop into T-memory cells; produce interleukins to stimulate phagocytosis or B-cells to divide or the development of T-killer cells specific to the antigen.
Define immunity
The means by which the body protects itself from infection
Define immunisation
The process of artificially creating immunity
Give the 4 types of immunity
- Natural active
- Natural Passive
- Artificial Active
- Artificial Passive
What is natural active immunity?
Organism’s own immune system is stimulated by a disease
What is natural passive immunity?
Antibodies are passed to an individual e.g. via breastmilk or placenta
What is artificial active immunity?
Organism’s own immune system is stimulated by a vaccine - dead or weakened pathogen. e.g. polio, MMR.
What is artificial passive immunity?
Antibodies obtained chemically and administered often by a jab
How do vaccinations work?
They promote primary response via clonal selection
B- and T-lymphocytes make memory cells which divide via mitosis (clonal expansion)
What is herd immunity?
The protection gained by a community when vaccination rates are very high
Name the two types of passive plant defences against pathogens
Physical and chemical
Name 5 physical plant barriers
- Wax
- Cuticle
- Cell wall
- Stomata
- Callose deposition in plasmodesmata to isolate healthy cells from infected ones
Name 4 chemical plant barriers
- Nutrient deprivation
- pH
- Phytoanticipins
- Insecticides, antibacterial and antifungal compounds
