Module 4 Flashcards
Pathogen =
a microorganism that causes disease.
Bacteria
• Can rapidly multiply in the right conditions • Cause disease by damaging cells or producing toxins that are harmful • Eg tuberculosis, bacterial meningitis, ring rot (plants)
Viruses
• Invade cells and take over the protein-synthesising organelles • Infect the cells with new DNA • Host cells eventually burst and release new copies of the viral DNA • Eg HIV/AIDS, influenza, tobacco mosaic virus (plants)
Fungi
• In animals, cause redness and irritation • This is due to hyphae released from the fungus • Eg black sigatoka (bananas), ringworm (cattle), athlete’s foot
Protoctista
• Feed on cell contents as they grow • Eg malaria, potato blight
Tuberculosis • Cause
• Bacterial • Mycobacterium tuberculosis • Divides slowly (every 20 hours) • Can survive for 6 months outside body
HIV/AIDS • Cause
• Virus • Human immunodeficiency • Attacks and destroys immune cells weakens immune system • Open to range of opportunistic diseases • Secondary infection
Malaria • Cause
• Eukaryotic organism • Plasmodium falciparum
Tuberculosis • Transmission
• Sufferer cough, catapulting droplets of saliva into air • Saliva contain tuberculi bacilli • High speed • Reach over 1-2m • 1 sneeze can have up to 40,000 droplets
Tuberculosis • Global Impact
worldwide • 1% of world newly infected each year • 8.8 million cases • 34% new cases occur in S.E. Asia • 1.6 million deaths
HIV/AIDS Transmission
• Exchange of bodily fluids • Sharing of hypodermic needles • Across placenta during child birth • From mother to baby during breast feeding • Use of unsterilized surgical equipment
HIV/AIDS Global Impact
• Worldwide • 45 million sufferers • 5 million new infections annually • 30 million have died • Rapidly rising in China
Malaria • Transmission
• Spreads by vector • Malarial parasites live in red blood • Feed on hemoglobin • Mosquito will suck parasitical gametes into its stomach • Gametes fuse to form zygotes in mosquito stomach • Plasmodium develops and moves to salivary glands • Mosquito bites person, injecting saliva • Plasmodium enters person • Migrates to liver • Multiplies and passes into blood • Cycle repeats
Malaria • Global Impact
• Kills 3 million annually • 300 million affected worldwide • limited to regions where anopheles mosquito can live
The most common means of transmission can be identified as five groups
Droplet transmission Physical contact • Faecal-oral transmission Transmission by spores Vector transmission
Droplet transmission
○ E.g. through sneezing - pathogen is contained within mucus ○ Type of direct transmission
Physical contact •
○ Common for skin diseases like ringworm, a fungal disease in cattle, which is spread by an infected animal brushing against an uninfected animal Direct transmission
Faecal-oral transmission
○ E.g. E. coli ○ Transmitted by consumption of food or water with traces of faeces from infected animal ○ Direct transmission
Transmission by spores
○ Spores are a resistant form of the pathogen ○ They can resist extremes of temperature, pH, and even strong disinfectants ○ E.g. anthrax ○ Direct transmission
Vector transmission
○ E.g. malaria ○ The pathogen is carried from one host to another via a vector ○ With malaria the vector is female mosquitoes ○ The pathogen cannot be spread directly from one host to another ○ Indirect transmission
how climate can also contribute to the spread of disease.
• Some vectors only live in hot climates, e.g. mosquitos carrying malaria • Many viruses, protoctists and bacteria survive better in warm climates • Very cold climates can kill pathogens
how Environment can also contribute to the spread of disease.
• Cramped and crowded environments are conducive to spread of disease ○ Droplet infection rate likely to be higher ○ Contact infection also much higher • Dirty environments harbour pathogens ○ E.g. using human sewage to fertilise crops is sometimes done in parts of the world ○ This is likely to cause the spread of faecal-oral pathogen spread
plant Physical barriers
• Passive • Cellulose cell wall • Lignin thickening of cell walls • Waxy cuticles • Bark • Closed stomata • Callose ○ Large polysaccharide deposited in sieve plates in phloem ○ Block movement of pathogens up and down plants to avoid infection of the entire plant • Tylose ○ Balloon-like swelling in xylem ○ Blocks xylem and stops pathogens from travelling this way around the plant
Production of chemicals passive
Terpenoids • Phenols • Alkaloids • Hydrolytic enzymes
Production of chemicals Active defences
Leaves sense presence of pathogens • Begin to prioritise use of energy in secreting harmful chemicals • Cellulose produced to further fortify the cell walls • Oxidative bursts: produce harmful oxygen molecules to target the pathogen
Primary defences
are those that prevent pathogens from entering the body
Secondary defences
are those that prevent pathogens from harming the body once it has infected the host.
Non-specific defences
are those which occur in the same way, no matter the pathogen, and don’t require identification of the antigen.
Specific defences
are immune responses carried out by the host which specifically target the pathogen.
Primary, nonspecific defences against pathogens in animals
Skin Inflammation Mucous Membranes Blood Clotting & Skin Repair Coughing and Sneezing
Skin
• Epidermis ○ Tough outer layer ○ Secretes sebum to waterproof skin ○ Keratin secreted, toughening skin ○ 20-30 cells thick • Dermis ○ 20-40 x thicker than epidermis ○ Contains sensory receptors cells, capillaries and hair follicles • Lower layers of the skin are site of cell division • Replace cells lost from surface • Sebaceous glands secrete lactic acid and fatty acids ○ Forms acidic environment ○ Disrupts bacterial processes
Mucous Membranes •
Lining of organs involved in protection and absorption • Present at most interfaces between body and external environment • Secrete sticky mucus and lysosomes enzymes • Can be lined with cilia
Blood Clotting & Skin Repair
• Body prevents excess blood loss • Clot acts as temporary seal • Prevents infection and first step in skin reparation • Requires calcium ions and 12 cofactors ○ Clotting factors • These initiate and see through the clotting cascade • After the clot, a scab forms, and the epidermis heals more permanently
Inflammation
• Caused by damaged cells • Damaged cells release histamines ○ Cause capillaries to dilate ○ Increase tissue fluid ○ Increase flood supply ○ Increased phagocyte supply • Damaged cells release chemokines ○ Chemicals to which cells can show chemotaxis ○ Attracts phagocytes • Phagocytes invade the tissues ○ Carry out phagocytosis
Coughing and Sneezing
• Reflexes that expel pathogen trapped in mucous • Effectively removes pathogen from airway tract
cells involved in the mucus-cough reflex
Goblet cells in trachea secrete gel-like mucus • Mucus traps pathogens and irritants that are inhaled • Cilia cells lining respiratory tract waft mucus towards the back of the throat • Cough reflex expels mucus and clears the airway
Phagocytes are .
a type of white blood cell (WBC), whose role is to trap pathogens and kill them. Phagocytes contain phagosomes: membrane bound organelles, which act as receptors, binding antibodies to the already pound pathogens. They may be assisted by proteins called opsonins.
note
• Pathogens can be recognized as foreign by chemicals markers on outer membrane called antigens • These are specific to the organism • Proteins in the blood, called antibodies, attach to these foreign antigens
Neutrophils
○ Multilobed nucleus - enhances flexibility of cell ○ Manufactured in bone marrow ○ Short lived ○ Released in large numbers
Macrophage
○ Larger cells ○ Manufactured in bone marrow ○ Tend to settle in organs, particularly lymph nodes
Phagocyte mode of action
Phagocyte envelopes and engulfs the pathogen • The membrane folds inwards: phagocytosis • Pathogen is trapped inside in vacuole called the phagosome • Lysosome fuse with the phagosome forming phagolysosome • Release enzymes into it, called lysins. • Lysins digest the bacterium • Products of the digestion are entirely harmless • Nutrients can then be absorbed into the cytoplasm or exocytosed into extracellular fluid
specific immune response contains
B and T cells They are white blood cells which have specialised receptors on their cell surface membrane. Their overall role is to produce antigens which neutralise the pathogenic antigen.
B Cells (B lymphocytes) can be…
• Plasma cells ○ Circulate in blood ○ Produce and secrete antibodies into circulation • B memory cells ○ Remain in the body for many years after the initial infection ○ Serve to ‘remember’ the antigen
T Cells (T lymphocytes) can be…
• T helper cells ○ Release cytokines ○ Stimulate B cell maturation ○ Promote phagocytosis • T killer cells ○ Identify and kill infected host cells ○ Especially important during viral infections• T memory cells ○ Long-term immunity • T regulator cells ○ Recognise when the pathogen has been removed and is no longer a threat ○ Alerts the rest of the immune system that it no longer needs to be active ○ Immune response ends
Other elements of the Specific Immune Response:
InflammationPhagocytesAntigen Presentation Antigen Recognition Clonal SelectionClonal Expansion Cell signalling
Inflammation and Phagocyres
• Attracts phagocytes • Attracted by chemotaxis
Phagocytes
• Phagocytes engulf and destroy pathogens in phagocytosis
Antigen Presentation
• Macrophages engulf pathogens • Do not fully digest it • Separate antigens • Display antigens on their surface • Become antigen-presenting cell (APC) • This attract lymphocytes which can neutralize the antigens
Antigen Recognition
• Cytokines produced by antigens attract T-helper cell • Thousands of different T-helper cells, which fit to different antigens • Effectiveness of T-helper cells depends on the closeness of the bonds
Clonal Selection •
Bound T-helper cells produce cytokines • Attract B-lymphocytes • Best fitting lymphocyte binds to the macrophage • Occurs in lymph nodes
Clonal Expansion •
Cytokines produced by T-helper cells cause B-lymphocytes to divide • Multiple B-cells produced • Rapid clonal expansion can cause mutations ○ As a result, increasingly close matches may be found • B-cells released into the bloodstream • Some B-cells make memory cells and are stored in glands and retained for life • Remaining B-cells circulate in the blood plasma • May become plasma cells, producing antibodies • Antibodies are produced in the blood on a large scale
Cell signalling
• Cells need to communicate to work effectively • This is achieved through release of cytokines and cell surface receptors • Receptors must be complementary to the signaling molecule ○ T and B lymphocytes have receptors that are complementary to the foreign antigen ○ When the antigen is detected, the lymphocyte is stimulated ○ Specialist surface receptors detect chemicals signals
Structure of Antibodies
• 4 polypeptide chains held together by disulphide bridges • Constant regions, which remains the same • Variable region which changes • Hinge regions, which allow for flexibility
• Primary Infection
○ When an infecting agent is first detected, it takes a few days for antibodies to be produced ○ Once pathogens have been dealt with, number of antibodies in the blood drops rapidly
• Secondary Infection
○ Antibodies do not stay in the blood ○ If the same infection occurs, antibodies must be produced again ○ This time, antibody production is much more rapid ○ Concentration of antibodies rise sooner and reaches a higher concentration
The overall, main action of antibodies is neutralisation. describe hrw process
• Attach to antigen on pathogen • Blocks binding site, preventing pathogen from binding to host cells
Antibodies can be grouped into 3 categories hat are they
• Agglutinins Antitoxins • Opsonins
• Agglutinins ○
Large antibody can bind many pathogens together ○ Immobilises them ○ Prevents them from entering cells as they are now part of a much biggers structure ○ Aids phagocytosis
Antitoxins
○ Antibodies can also bind to toxins released by the pathogens, rendering them harmless
Opsonins
○ Antibodies can label the pathogens as foreign to phagocytes ○ Speeds up the process of phagocytes identifying antigens
Artificial Active •
• Immunity provided by antibodies made as result of injection • Person injected with weakened virus, activating the immune system
Natural
Active •
• Immunity provided by antibodies made in immune system as a result of infection • Person suffer from diseases only once, then is immune
Artificial Passive •
• Immunity provided by injection of antibodies made by another individual
Natural
Passive •
• Antibodies provided via the placenta or breast milk • Makes baby immune to diseases that the mother is immune to • Very useful in the 1st year, when baby’s immune system is developing
Autoimmune diseases
e diseases that evolve when a person or animal’s immune system attacks a part of the host body, in absence of pathogenic infection. During clonal selection, lymphocytes that are programmed to attack ‘self’ are normally destroyed before entering the bloodstream.
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