Communicable Diseases Flashcards
What is a pathogen?
An organism which causes disease
Passive Physical plant defences
Cellulose cell wall - physical barrier
Lignin cell wall - waterproof, almost indigestible
Bark - contains chemicals to defend against pathogens
Waxy cuticle - prevents water collecting on the cell surfaces, creates absence of water which pathogens need to survive
Closed stomata - when pathogen detected to prevent pathogens entering
Callose - deposited around sieve plates and blocks flow in sieve tube, preventing spread of pathogens
Tylose - plugs xylem vessel, preventing water flow and blocks pathogen, contains toxins to pathogens
Passive Plant chemical defences
Plant tissues - contain anti pathogenic properties e.g terpenoids, or phenols, alkaloids, hydrolytic enzymes
Terpenes in tyloses and tannins in bark are present before infection
Why are chemical defences made after the infection is detected in plants?
Production of chemicals requires lots of energy
Active physical plant defences
Cell wall - becomes thickened and strengthened with cellulose
Oxidative bursts - produce highly reactive oxygen molecules to damage pathogen cells
Callose - deposited between plant cell wall and cell membrane to prevent cell penetration
Necrosis - deliberate cell suicide
How does Mycobacterium tuberculosis cause disease?
Triggers response by infecting phagocytes in the lungs
Infected phagocytes are sealed in waxy coated tubercles so bacteria remains dormant
If another factor weakens immune system, bacteria becomes active and destroys lung tissue
How does HIV result in aids?
Attachment proteins bind to complementary CD4 receptors
HIV particles replicate inside cells killing or damaging them
AIDS develops when there are too few Th cells for immune system to function
Describe 3 fungal infections
Black Sigatoka
Ring worm
Athletes foot
How are communicable pathogens transmitted directly?
Inhalation
Skin to skin contact
Passively through wounds
Hoe are communicable pathogens transmitted indirectly?
Consumption of contaminated food
Via a vector
Spores
4 physical barriers to pathogens in plants
Cellulose cell walls
Lignified layer
Waxy upper cuticle
Old vascular tissue is blocked to prevent pathogens spreading inside plant
2 mechanical responses to pathogens in plants
Guard cells close stomata
Thick polysaccharide Callose depositors between cell wall and plasma membrane to limit spread
Describe chemical defences plants use against pathogens
Terpenoids (essential oils) e.g methols act as antibacterials
Phenols e.g tannin inhibit insects from attacking by interfering with digestion
Alkaloids e.g caffeine and morphins deter herbivores from feeding due to bitter taste
Defensins inhibit transport channels
Hydrolytic enzymes e.g chitinases which break down cell wall of invading organisms
5 barriers to infection in animals
Skin is a tough keritinised layer
Blood clotting prevents access through cuts
Hydrochloric acid in stomach kills bacteria
Harmless bacteria in gut which increases interspecific competition with pathogens
Mucous membranes to trap pathogens
Name 4 ways the non specific immune system responds to infection
Inflammation
Phagocytosis
Digestive action of lysosomes
Production of antiviral agents
Outline the process of inflammation
Damaged vessels release histamines, causing vasodilation
Blood flow and permeability of blood vessels increase
White blood cells and plasma move to infected tissue
How does blood clotting occur?
Blood platelets plug and release chemicals to enhance clotting e.g thromboplastin
Prothrombin changes into thrombin by thrombokinase
Fibrinogen changed to insoluble fibrin which covers wound
Name 2 types of white blood cell involved in phagocytosis
Neutrophils
Macrophages (can become antigen presenting cells)
How does phagocytosis destroy pathogens?
Phagocyte engulfs the pathogen by endocytosis to form a phagosome
Phagosome fuses with lysosome
Lysosome digests pathogen through hydrolysis leaving amino acids
Phagocyte then absorbs the products
Explain the role of antigen presenting cells
Macrophage display antigen from pathogen on its surface
Enhances recognition by Th cells which cannot directly interface with pathogens
Secrete cytokines which stimulate specific immune response
What is an antibody? Describe its structure
Proteins secreted by plasma cells
2 light chains held by disulphide bridges, 2 longer heavy chains. 4 polypeptide chains
Binding sites on variable region of light chains have specific tertiary structure which is complementary to an antigen
The rest is the constant region which binds to phagocytes
How do antibodies lead to the destruction of a pathogen?
Agglutination from antigen antibody complexes to enhance phagocytosis
Activation of a complement
Opsonises mark microbes for phagocytes
Antitoxins make toxins insoluble
Compare passive and active immunity
Passive
- no memory cells and antibodies not replaces so is short term
- immediate
- antibodies from external source
- no direct contact with antigen needed
Active
- memory cells produced so long term
- time lag
- lymphocytes produce antibodies
- needs direct contact with antigen
Examples of passive and natural immunity
Passive neutral - antibodies in breast milk / placenta
Passive artificial - anti venom, needle stick injections
Active natural - humoral response to infection
Active artificial - vaccination
What are neutrophils and their characteristics?
- most common
- multi lobed nucleus
- made in bone marrow
- contain lysosomes
- engulf and digest pathogens
What are macrophages and their characteristics?
- less common
- travel in blood as monocytes
- indicate specific response to pathogens
- more mature
- mostly in lymph nodes
- antigen from pathogen forms a special protein complex on surface of the cell becoming an APS
- displays antigens for other immune cells to recognise
- presented with MHC II cells so recognised as ‘self cells’
What is the role of B cells in a specific immune response?
Make antibodies
Where are B cells produced?
Bone marrow
What is the role of T cells?
Destroy infected body cells
Where are T cells produced?
Produced in the thymus
What are the two types of B cells and what do they do?
Plasma B cell - circulate in the blood making and releasing antibodies
Memory B cells - remain in the body for years as immunological memory
What are the 4 types of T cell and what are their roles?
Killer T cell (cytotoxic) - kill infected body cells
Helper T cells - release cytokines to stimulate B cell development and stimulate phagocytes
Memory T cell - stay in blood and differentiate into Tk or Th cells in reinfection
Regulator T cells - shut down immune response after pathogen neutralised to prevent auto immunity
