Communicable Diseases, Disease Prevention And The Immune System Flashcards
Name 4 groups of pathogen that can cause communicable diseases
Bacteria, Fungi, Protocista, Viruses
Describe 2 fungal infections
Cattle Ringworm - Direct Contact with infected cattle
Athletes Foot - Direct Contact with fomites touched by infected individuals
How are communicable pathogens transmitted directly ?
Droplet transmission -Breathing in infected droplets (coughing, sneezing, talking, spitting of an infectious person.)
Sexual transmission - Having unprotected sexual intercourse with an infectious person (exchange of bodily fluids)
How are communicable pathogens transmitted indirectly ?
Water and food - Infectious person sheds the pathogen into a water/food, which is then consumed by another person
Spores - Products of asexual reproduction, produced by organisms such as fungi, and some protoctist species. Have the ability to cause disease when they gain entry into hosts
Vectors - Organisms which are first infected with the pathogen before passing the disease onto the final host. E.g. in malaria, infected mosquitoes act as vectors by spreading the causative protoctist to humans
How do living conditions affect disease transmission ?
Overcrowding increases direct transmission
Climate determines which organisms can survive e.g. malaria is more prevalent in tropical countries, where mosquito (vector) can breed
Social factors influence how quickly people are treated, which can increase/decrease direct transmission
Name 4 physical barriers to pathogen entry in plants
Cellulose cell walls
Lignified layer
Waxy upper cuticle
Old vascular tissue is blocked to prevent pathogens from spreading inside the plant
Describe 2 mechanical responses to infection in plants
Guard cells close stomata
The thick polysaccharide callose is produced & deposited between the cell wall & plasma membrane to increase entry distance/limit spread
What is necrosis ?
Injury activates intracellular enzymes in plants that kill cells near the site of infection to prevent pathogen from spreading
Describe the chemical defences plants use against pathogens
Terpenoids (essential oils) e.g. menthols act as antibacterials.
Phenols e.g. tannin inhibit insects from attacking by interfering with digestions
Alkaloids e.g. caffeine & morphine deter herbivores from feeding because they taste better
Defensins Inhibit transport channels
Hydrolytic enzymes e.g. chitinases break down cell wall of invading organisms
Name 5 barriers to infection in animals
Skin is tough keratin layer
Blood clotting prevents pathogens from entering through skin lesions
Hydrochloric acid kills bacteria
Harmless bacteria in gut & on skin surface increase interspecific competition with pathogens
Mucous membranes trap pathogens and may secrete anti microbial enzymes
What are expulsive reflexes ?
Body attempts to force foreign substances out:
- Irritation of mucous membranes in nostrils causes sneezing
Irritation of ciliates epithelium in respiratory tract causes coughing
Name 4 ways the nonspecific immune systems responds to infection
Inflammation
Phagocytosis
Digestive action of lysozymes
Production of interferon (antiviral agent)
Outline the process of inflammation
Damaged vessels release histamines
, causing vasodilation
Blood flow & permeability of blood vessels increase
White blood cells & plasma move into the infected tissues
How does blood clotting occur ?
Blood platelets form plug & release chemicals that enhance clotting
Prothrombin changes into thrombin, its active form
Fibrinogen changes into insoluble fibrin which covers wound
Name the 2 types of white blood cells involved in phagocytosis
Neutrophils
Macrophages (can become APCs)
How does phagocytosis destroy pathogens ?
Phagocyte moves towards pathogen which may have been marked by opsonise via chemotaxis
Phagocyte engulfs pathogen via endocytosis to form a phagosome
Phagosome fuses with lysosomes (phagolysome)
Lysozymes digest pathogen
Phagocyte absorbs the products from pathogen hydrolysis
Explain the role of antigen-presenting cells (APCs)
Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)
Enhances recognition by T(helper) cells, which cannot directly interface with pathogens/antigens in bodily fluid
Secrete cytokines that are involved in stimulating specific immune response
What are lysozymes ?
Digestive enzymes. Found in lysosomes as well as many secretions e.g. tears & mucus. Damage bacterial cell walls, causing osmotic lysis
Outline how to prepare blood to be observed under a microscope
Smear a drop of blood onto a slide using a spreader held at 45*
Add leishman stain then a buffer rinse
Name the 2 types of specific immune response
Cell-mediated
Humoral
Outline the process of cell-mediated response
Complementary T(Helper) lymphocytes bind to foreign antigen on APC
Cell signalling via secretion of interleukins stimulates:
- a clonal expansion of complementary T(Helper) cells (Rapid mitosis): become memory cells or trigger humoral response
- clonal expansion of cytotoxic T cells: secrete enzyme perforin to destroy infected cells
Outline the process of the humoral response
Complementary T(Helper) lymphocytes bind to foreign antigen on antigen-presenting T Cells
Release cytokines that stimulate clonal expansion (Rapid mitosis) of complementary B lymphocytes
B Cells differentiate into plasma cells
Plasma cells secrete antibodies with complementary variable region to antigen
Describe the structure and function of B and T lymphocytes
Many specific receptors & immunoglobulins on surface
B cells differentiate into plasma cells to secrete antibodies
3 Types of T Cell: T helper (secrete cytokines), T killer (secrete perforin), T regulator (Supress other immune cells to prevent autoimmune disease)
What is antibody? Describe its structure
Proteins secreted by plasma cells
Quaternary structure: 2 ‘Light chains’ held by disulphide bridges, 2 longer ‘heavy chains’
Binding sites on variable region of light chains have specific tertiary structure complementary to an antigen
The rest of the molecule is known as a the constant region
Refer To GoodNotes
How do antibodies lead to the destruction of a pathogen ?
Agglutinins form antigen-antibody complexes to enhance phagocytosis
Activation of complement
Opsonises mark microbes for phagocytes
Antitoxins are toxins insoluble via precipitation/ neutralisation
What are memory cells ?
Specialised T(Helper)/B cells produced from primary immune response
Remain in low levels in the blood
Can divide very rapidly by mitosis if organism encounters the same pathogen again
Contrast the primary and secondary immune response
Secondary;
- Faster rate of antibody production
- Shorter time lag between exposure & antibody production.
- Higher concentration of antibodies
- Antibody level remains higher after the secondary response
- Pathogen usually destroyed before any symptoms
Compare and contrast passive and active immunity
Both involve antibodies & can be natural or artificial
Passive: no memory cells & antibodies not replaced when broken down = short-term
Immediate
Antibodies from external source
No direct contact with antigen necessary
Active: Memory cells produces = long-term
Time lag
Lymphocytes produce antibodies
Needs direct contact with antigen
Give examples of passive and active immunity
Passive natural: antibodies in breast milk/across placenta
Passive artificial: anti-venom, needle stick injections
Active natural: humoral response to infection
Active artificial: vaccination
Define ‘Autoimmune disease’ and give examples
Immune system produces antibodies against its own tissues
Rheumatoid arthritis: immune system targets synovium lined joints, causing inflammation
Lupus: Results in inflammation throughout body
Explain the principles of vaccination
Vaccine contains dead/inactive form of a pathogen or antigen
Triggers the primary immune system
Memory cells are produced and remain in the bloodstream, so secondary response is rapid & produces a higher concentration of antibodies
Pathogen is destroyed before it causes symptoms
Define endemic and epidemic
Endemic: disease occurs routinely in a geographical area
Epidemic: temporary rapid increase in incidence of disease in a geographical area
What role do vaccines play in preventing epidemics ?
Routine vaccinations of 80%-90% of population reduces available carriers of pathogen, resulting in herd immunity. Limited by country’s resources
Vaccinating close contacts of infected individual limits spread of pathogen, but raises issues of distributive justice
Programs have changed to account for informed consent & maximum beneficence even during epidemic
What are the benefits of using antibiotics to treat bacterial infection ?
Effectively reduce population of bacterial colony. Used widely since discovery of penicillin in mid-20th century
What are the risks of using antibiotics to treat bacterial infection ?
Overuse of antibiotics increases selection pressure for resistant strains of bacteria. Antibiotic-resistant infections e.g. caused by MRSA & Clostrdium difficult Are difficult to teat
