Topic 6.3: Defence Against Infectious Disease Flashcards Preview

IB Biology > Topic 6.3: Defence Against Infectious Disease > Flashcards

Flashcards in Topic 6.3: Defence Against Infectious Disease Deck (29)
Loading flashcards...


Pathogens are disease-causing agent that disrupt the normal physiology of infected organisms


Zoonotic Diseases

Diseases that can be naturally transmitted between
animals and humans


Lines of Defense

1st line of defense – Surface barriers (skin / mucus)
2nd line of defense – Innate immunity (non-specific)
3rd line of defense – Adaptive immunity (specific)


First line of defense against infectious disease

Surface barriers that function to prevent pathogenic entry
-Mucous Membranes



1) Protects external structures (i.e. outside the body)
2) Thick, dry and composed predominantly of dead cells
3) Glands secrete chemicals to restrict bacterial growth


Mucous Membranes

1) Protects internal structures and cavities (inside body)
2) Thin region composed of living cells that secrete fluid
(mucus) to trap pathogens (which may then be removed)



Compounds that target prokaryotic features
but don’t harm eukaryotic cells (i.e. don’t affect host organism). May target:
1) Structures (e.g. cell wall)
2 Metabolic processes


Antibiotics Resistance

1) Some strains of bacteria have evolved with genes that confer resistance to antibiotics
2) Antibiotics can’t be used to treat viruses (no metabolism)



The first antibiotic identified was penicillin (Fleming – 1928)
• Its treatment use was demonstrated by Florey and Chain


Blood Clotting

Clotting seals damaged vessels to prevent pathogenic entry


Coagulation Cascade (5)

1) Injured cells and platelets release clotting factors
2) These factors convert prothrombin into thrombin
3) Thrombin converts fibrinogen (soluble) into fibrin (insoluble)
4) Fibrin forms a mesh of fibres that block the injured site
5) Clotting factors also cause platelets to become sticky and form a solid plug (called a clot), sealing the wound


Innate Immune System

1) They are non-specific (i.e. they do not differentiate between different types of pathogens)
2) They are non-adaptive (i.e. they produce the same response to every infection – there is no immunological memory)


Lymphatic System

The lymphatic system is a secondary transport system that protects the body by producing and filtering lymph



1) Lymph is a clear fluid rich in white blood cells that arises from the drainage of interstitial fluid from the tissues
2) Lymph is filtered at lymph nodes, whereby pathogens are removed and the fluid is returned to venous circulation



Tissue damage causes mast cells to release histamine, which triggers vasodilation and increased capillary permeability
• This improves the recruitment of white blood cells


Side effects of an inflammatory response

1) Vasodilation = localised redness & heat (⇧ blood flow)
2) Capillary permeability = swelling & tenderness (⇧ fluid)



Fever is an abnormally high body temperature (due to infection)
1) It increases metabolism and activates heat shock proteins
2) It reduces the growth rate of infectious pathogens


Occurrence of Fever

Fever occurs when white blood cells release cytokines
1) This causes the hypothalamus to produce prostaglandin
2) Prostaglandin increases the temperature of the body



1) Macrophages and dendritic cells migrate via the blood to sites of infection (damaged cells release chemotactic agents)
2) The pathogens are surrounded by extensions (pseudopodia) and are then internalised within a vesicle (via phagocytosis)
3) The vesicle may fuse with a lysosome to digest the pathogen
• Fragments (antigens) are presented on the surface of the cell in order to activate the third line of defense (adaptive)


Complement System

Inactive complement proteins are produced by white blood cells and certain body cells (particularly the liver)
1) Opsonisation (increase pathogen recognition by phagocytes)
2) Chemotaxis (recruitment of phagocytes to the infection site)
3) Membrane attack (forms a complex that ruptures cell walls)


Natural Killer Cells

A class of non-specific lymphocytes that can target and destroy infected body cells or tumor cells
1) Infected cells release chemicals called interferons, which function to promote the activation of natural killer cell
2) Natural killer cells induce apoptosis in the infected cell


Adaptive Immunity

1) They are specific (i.e. they can differentiate between different types of pathogens and respond accordingly)
2) They are adaptive (i.e. they produce a heightened response upon re-exposure – there is immunological memory)



Substances that the body recognise as foreign and that can elicit an immune response


Presentation of Antigens to Lymphocytes

Antigens are presented to lymphocytes via identification
markers on the surface of native cells (MHC molecules)
1) MHC I markers are found on all body cells (except RBCs) and present endogenous antigens (cell-mediated response)
2) MHC II markers are on innate immune cells (macrophages) and present exogenous antigens (humoral response)



Antibodies are proteins produced by B lymphocytes that are specific to a given antigen (they are also called immunoglobulins)


Humoral Immunity (targets ‘non-self ’)

• B cells each produce one specific type of antibody
• Macrophages or dendritic cells present antigen fragments
(via MHC II markers) to helper T lymphocytes (TH cells)
• TH cells release cytokines and activate the antigen-specific
B cells (which rapidly divide to form many plasma cells)
• The plasma cells make antibodies specific to the antigen
• A small proportion of B cell clones differentiate into
long-lasting memory B cells (for long-term immunity)


Cell Mediated Immunity (targets ‘self ’)

1) Infected cells present antigens on their MHC I markers
2) Antigens are recognised by cytotoxic T cells (and TH cells)
3) Cytotoxic T lymphocytes (TC cells) bind to the infected cell and trigger its destruction (via perforating enzymes)
4) TH cells stimulate the formation of memory TC cells
5) TC cells can target virus-infected cells and tumor cells
6) Suppressor T cells regulate the action of TC cells to prevent sustained T cell activation (i.e. autoreactivity)


Immunodeficiency (AIDs)

1) HIV is a retrovirus that infects helper T cells (TH cells)
2) It is usually transmitted via the exchange of bodily fluids
3) HIV is integrated into the genome of infected TH cells
4) After a prolonged period of inactivity, it becomes active and lyses the TH cell as it begins to spread
5) This results in an inability to produce antibodies and a general loss of immunity (disease is called AIDS)


Hypersensitivity (Allergies)

1) Allergens are substances that trigger an immune response despite not being inherently harmful (e.g. peanut allergy)
2) When a B cell is activated by an allergen, it makes large
quantities of allergen-specific antibodies (IgE)
3) These IgE antibodies bind to mast cells and ‘prime’ them
4) Upon re-exposure to the allergen, the sensitised mast cells release large quantities of histamine (causes inflammation)
5) This inflammatory response is called an allergic reaction