response to infection Flashcards
what happens if the body’s defence mechanisms against invading organisms are overcome?
the invaders may cause disease
infectious diseases
diseases that are spread from one person to another
pathogens
disease causing organisms
most common pathogens that affects the body
bacteria and viruses
+ fungi and animal parasites also affect the body (not main focus)
bacteria structural characteristics
- cell wall
- no nucleus (prokaryotes)
- flagellum present
- DNA in the form of plasmids
majority of bacteria is…
non-pathogenic
uses of bacteria
- essential to life e.g. decomposition of organic material
- industrial processes
location of bacteria
live in skin & inside intestines
effects of bacteria
producing toxins & inducing allergic responses
how to identify bacterium
grown on an agar player/growth medium in specific conditions → stained → viewed under microscope
viruses definition
microscopic infectious agents
virus structure
all contain genetic material in the form of DNA or RNA (but never both)
- consist of a protein sheath surrounding a core of nucleic acid
- some also have an external lipid envelope
reproduction of viruses
totally dependent on living cells for reproduction, infect a living cell and it’s DNA/RNA induces the cell to manufacture more virus particles, new virus particles leave the host cell → infect others, cells become damaged/changed or die
viruses: living or non-living?
not living things - cannot reproduce by themselves
why are symptoms from a virus affecting specific tissues?
viruses differ in the type of cell they invade, symptoms relate to the affected tissue
what happens when a virus infects bacteria?
bacteriophage is made
contagious disease
communicable disease may be spread by the transmission of pathogenic organism from one person to another
vectors
intermediate host of the pathogen that spread the infectious disease e.g. fleas, mosquitoes
ways of transmission of pathogens
- transmission by contact
- ingestion of food or drink
- transfer of body fluids
- infection by droplets
- airborne transmission
- transmission by vectors
transmission by contact w. examples
- spread of pathogen by physical contact
- direct = actually touching infected person
- indirect = touching an object that has been touched by infected individual
- e.g. skin infections, STIs
ingestion of food or drink w. examples
- contaminated with pathogens
- e.g. salmonella food poisoning, dysentery
transfer of body fluids w. examples
- when blood or other fluids from an infected person comes into contact with mucous membranes (nose, throat, mouth, genitals, bloodstream) of another uninfected person
- via a needle stuck; break in the skin
- e.g. HIV, Hep B and C
infection by droplets w. examples
- tiny droplets of moisture containing pathogenic organisms are admitted when breathing, talking, sneezing or coughing
- may be breathed in by others; settle on food or utensils to be later ingested with food
- e.g. Ebola, COVID-19, mumps, cold, flus
airborne transmission w. examples
- moisture in exhaled droplets evaporate, most bacteria are killed, but viruses and some bacteria remain viable → cause infection when inhaled
- particles are lighter → remain viable for greater distance than those transmitted by droplets
- e.g. measles, chickenpox
transmission by vectors w. examples
- animals such as insects, ticks or mites
- some vectors transfer the pathogen directly
- some may spread the pathogen to food or water → injected (e.g. houseflies)
- Many vector-borne disease are spread by specific vector
- e.g. malaria is spread by mosquitoes; lyme disease spread by ticks
non-specific defences
defence of the body that acts against all pathogens
specific defences
directed against a specific pathogen
external defence: skin
- covers outside of the body
- good at stopping entry of microorganisms (provided there are no cuts/abrasions)
- special protection at openings in skin (mouth, eyes, anus)
- normal bacteria occupy skin → pathogens find it difficult to establish
what do External defences do?
stop pathogens and foreign particles from entering
additional mechanisms of the skin
Sebum and sweat
sebum
oily, waxy secretion from sebaceous glands; kills pathogenic bacteria
sweat
liquid produced by sweat glands; contains salts and fatty acids that prevent growth of many micro-organisms
external defence: mucus
Mucous membranes secretes mucus = slippery, stringy substance
- Traps particles → inhibits entry of microorganisms to the organs of the body
- Eg, digestive, urinary and reproductive tracts
mucous membranes
epithelial tissue that secretes mucus and lines many body cavities
external defence: hair
- Found in the nasal cavity and ears
- Hairs + layer of mucus = trap up to 90% of particles inhaled when breathing
external defence: cilia
- Cilia = hair like projections from a cell; beat rhythmically to move material across a tissue surface
- Mucous membranes lining the nasal cavity and trachea have
cilia - Beating of the cilia moves mucus (containing trapped particles and micro-organisms) towards the throat → coughed or swallowed
external defence: acids
Stomach juices are strongly acidic (HCI)
- Kills many of the bacteria taken in with food or those contained in mucus swallowed from nose or windpipe
- Vagina has acid secretions → reduce growth of microorganisms
external defence: lysozyme
lysozyme = enzyme that kills bacteria
- found in tears, saliva and perspiration
external defence: cerumen
cerumen = ear wax
- Protects the outer ear against infection by some bacteria
- Slightly acidic
- Contains lysozyme
external defence: movement of fluid
Eg. Urine flowing through urethra = cleansing action
- Prevents bacterial growth
- Helps stop bacteria reaching the bladder and kidneys
what are protective reflexes?
Involuntary reflexes that help protect the body from injury
examples of protective reflexes
- Sneezing
- Coughing
- Vomiting
- Diarrhoea
sneezing
- Stimulus = irritation of the walls of the nasal cavity
- Irritation = Fumes; dust particles
- Forceful expulsion of air carries mucus, foreign particles and irritating gases out through nose and mouth
coughing
- Stimulus = irritation of lower respiratory tract (bronchi and
bronchioles) - Air is forced out of the lungs to try and remove the irritant
- Air drives mucus and foreign matter up the trachea → throat
and mouth
vomiting
- Contraction of abdominal muscles and diaphragm expels stomach contents
- Psychological stimuli, excessive stretching of stomach and bacterial toxins = induce vomiting
diarrhoea
- Irritations cause increased contractions of the muscles of the wall of the intestines → irritant removed ASAP
- Material doesn’t stay in the large intestine long enough for water to be absorbed
- Irritants = bacteria, viruses or protozoans
what attacks organisms that overtake the external defences
Organisms that penetrate our external defences are attacked by phagocytes
phagocytes
Phagocytes = specialised WBC (leucocytes)
what do phagocytes do?
engulf and digest micro-organisms and cell debris
- Eliminates many pathogens before an infection has the chance to take hold
different types of cells that are phagocytic
- Monocytes and macrophages
- Neutrophils
- Dendritic cells
Monocytes
type of leucocyte found in the blood that migrates into damaged tissues (infected or inflamed) - form macrophages
Macrophages
large phagocytic cell; derived from monocyte
what do macrophages do?
- Some move through tissues looking for and destroying pathogens
- Some are fixed; only deal with pathogens that come to them
- Important in removing microbes and dying cells through phagocytosis
neutrophils
- Granulated leucocyte (granules visible in their cytoplasm)
- Lobulated nucleus
lifespan of neutrophils
- Short life span (die after a few days)
- Dead cells = pus that forms after an infection
what do neutrophils do?
First cells to move into the tissue to destroy the pathogen by phagocytosis (important in killing pathogens inside cells)
dendritic cells
- Characterised by projections from the cytoplasm
- Different from macrophages and neutrophils = function goes beyond phagocytosis
- Ability to detect, engulf and process foreign particles
- Use info about ingested particles → assist with specific immunity
what is inflammation?
response to damage to a tissue; involves swelling, heat, pain and redness in the affected area
purpose of inflammation
- Reduce the spread of pathogens, to destroy them and prevent entry of addition pathogens
- Remove damaged tissue and cell debris
- Begin repair of the damaged tissue
four signs of inflammation
- Redness
- Swelling
- Heat
- Pain
what is a complement system?
system of proteins produced by the liver that enhance the activity of antibodies and phagocytes
what causes inflammatory repsonse?
damage to tissues
what is inflammatory response assisted by?
assisted by proteins produced by liver cells and macrophages
first step in inflammatory response
Mechanical damage or local chemical change → specialised leucocytes called mast cells to be activated by complement proteins
- Leads to release of histamine, heparin and other chemicals into the tissue fluid
second step in inflammatory response
Histamine increases blood flow through the are due to vasodilation
- Walls of blood capillaries more permeable → more fluid moves through capillary walls into tissue
- Increased blood flow → heat and redness
- Escape of fluid → swelling
third step in inflammatory response
Mast cells release heparin = prevents clotting in the immediate area of injury
- Clot of the fluid forms around damaged area
- Slows the spread of the pathogen into healthy tissues
fifth step in inflammatory response
Abnormal conditions in the tissue stimulate pain receptors in inflamed area
fourth step in inflammatory response
Complement system proteins and some chemicals released by the mast cells attract phagocytes (neutrophils) → consume micro-organisms and debris by phagocytosis
sixth step in inflammatory response
Phagocytes are filled by bacteria, debris and dead cells = die
- Pus formed from dead phagocytes and tissue fluid
seventh step in inflammatory response
New cells produced by mitosis → repair of damaged tissue
takes place
fever
elevation of body temperature above 37C
Change due to resetting of body’s thermostat (controlled by the hypothalamus) to a level higher than normal
what causes fever
- Reaction due to pyrogens released by WBC during inflammatory response and act on hypothalamus
- Pyrogens = substance that results in a fever
what is pyrogen?
Produced by activated macrophages, dendritic and epithelial cells
what happens at the start of a fever?
- Body temp is still regulated in response to heat/cold with a fever → set point is at a higher level
- Onset of fever is gradual - can be be rapid
- Person’s thermoreceptors detect body temp → hypothalamus
recognises it is lower than the new higher set point- Vasoconstriction in the skin and shivering occur
- Conserve heat and increase heat production (increasing body temp)
- Vasoconstriction in the skin and shivering occur
what happens when the fever breaks
- When fever breaks (crisis) → body’s thermostat set to normal
- Person feels hot and appears flushed → skin vasodilation and sweating (bring body temp down)
how are fevers beneficial?
- High body temp inhibits the growth of some bacteria and viruses
- Heat speeds up the rate of chemical reactions → help body cells repair themselves more quickly during disease
- May inhibit viral replication by allowing chemicals called interferons to operate more quickly
dangerous effects of fever
- If body temp goes too high → convulsions; brain damage
- Death will occur © 44.4 - 45.5C
what does lymphatic system consists of
- Network of lymph capillaries joined to larger lymph vessels
- Lymph nodes - located along the length of some lymph vessels
function of lymphatic system
Important part of body’s internal defence against pathogenic organisms
lymph nodes and phagocytosis
- Lymph entering lymph nodes contain cell debris, foreign particles and microorganisms that have penetrated the body’s external defence
- Some may be pathogenic
- Larger particles (g. Bacteria) are trapped in meshwork of fibres as lymph flows through spaces
in nodes- Macrophages ingest and destroy these by phagocytosis
what happens when infections occur?
formation of lymphocytes
increases
what is the immune system composed of?
Composed of cells and proteins that protect against foreign organisms,
range of alien chemicals, cancerous and other abnormal cells
immune response
Homeostatic response that helps to deal with the invasion of micro-organisms and foreign substances enter the body → restore to normal conditions
key cells involved in immune response
- B-cells
- T-cells
- Produced in bone marrow
- End up in lymphoid tissue
where do B cells mature
born marrow then move to lymphoid tissue
where do T cells mature
thymus then move to lymphoid tissue
what do b cells develop into?
Develops into either plasma cell that produces antibodies or a memory cell
what do T cells differentiate into?
Can differentiate into a no. of different kinds of cells that are involved
in cell-mediated immunity
antibody mediated immunity
involves the production of special proteins called antibodies by B cells, which circulate around the body and attack invading agents
cell mediated immunity
due to T cells and involves the formation of special lymphocytes that destroy invading agents
antigens
Any substance capable of causing the formation of antibodies when introduced into the tissues → causing a specific immune response
self-antigen
Molecules produced in person’s own body doesn’t cause IR
non-self antigens
Foreign compounds that trigger IR by being recognised by receptors on B and T cells
antibodies
Substance produced in response to a specific antigen; combines with the antigen to neutralise or destroy it
what group of proteins do antibodies belong to?
immunoglobins
what is it called when an antibody combines with an antigen?
antigen-antibody complex
how is an antigen-antibody complex made
- Antigen molecules have specific active sites with a particular shape
- Antibody has the complementary shape > allowing two molecules to fit together like a key in a lock
- Each antibody can combine with only one particular antigen
Antigen presenting cells
Phagocytic cells that digest pathogens and present the antigen to lymphocytes; include dendritic cells and macrophages
they:
- Detect the presence of a non-self antigen
- Engulf the antigen
- Digest the pathogen, producing small fragments that move to the surface of the cell
- Present the antigen to the lymphocytes
Primary response
- First exposure to antigen
- Slow response → days to build up large amounts of antibodies
- Time for B-cells to multiply and differentiate > plasma cells and secrete
antibodies - Declines after level of antibodies reached peak
Secondary response
- Second/subsequent exposure to same antigen
- Response faster → memory cells recognise the antigen more quickly
- Plasma cells are able to form quickly
- Antibody levels in body plasma rising rapidly to higher level that lasts longer
- Antigen has little opportunity to exert a noticeable effect on body = no illness
killer T cells (cytotoxic)
- migrate to the site of infection and deal with invading antigen
- Attach to the invading cells → secrete chemical that will destroy antigen
- Then go in search of more antigens
helper T cells
- Bind to antigen on antigen-presenting cells → stimulate secretion of
cytokines that:- Attract lymphocytes to infection site → sensitised and activated → intensifies response
- Attract macrophages to infection site → can destroy antigens by phagocytosis
- Intensity phagocytic activity of macrophages
- Promote the action of killer T-cells
suppressor T cells
- Act when the immune activity becomes excessive/infection dealt with successfully
- Release substances that inhibit T and B cell activity > slowing down IR
immunity
resistance to infection by invading micro-organisms
natural immunity
occurs without any human intervention
artificial immunity
produced by giving a person an antigen that triggers an IR; or giving them antibodies to an infecting antigen
passive
When a person receives antibodies produced by someone else
- Individuals body played no part in the production of antibodies
active immunity
Results when the body is exposed to a foreign antigen > makes
antibodies in response to that antigen
This type of immunity lasts longer than passive > presence of
memory cells
immunisation
programming the immune system to respond
rapidly to infecting microorganisms; developing immunity
vaccination
artificial introduction of antigens of pathogenic
organisms
vaccine
antigen preparation used in artificial immunisation
Live-attenuated vaccines
- Living attenuated microorganisms have reduced virulence (reduced ability to produce disease symptoms)
- Immunised person doesn’t contract the disease; but manufactures antibodies against the antigen
Inactivated vaccines
- Contain dead microorganisms
- Produce an immunity that is shorter lasting than immunisation using LA microorganisms
Toxoid vaccines
- Cases where bacteria produce their effects in humans by liberating toxins - not necessary to use the bacteria for immunisation
- Toxins produced by the bacteria can be inactivated → when injected they don’t make the person ill
- Inactivated toxins = toxoids
Sub-unit vaccine
Fragment of organism can be used to provoke IR
vaccines - Recombinant DNA
- Insert certain DNA sequences from the pathogen into harmless bacterial cells
- Chosen DNA sequence causes the production of antigens characteristic of the pathogen
- Vaccination with harmless bacterium → immunity against pathogen
vaccinations start at what age and why?
- Vaccination starts after 6 weeks of age
- Child’s blood contains antibodies from it’s mother via placenta and breast milk
- If given earlier than weeks, antibodies from mother will eliminate antigens
- 6 weeks gives newborn time for immune system to be activated
booster reason
- one injection of a vaccine isn’t enough to protect a person from particular disease
- Antibody levels from the primary response following first dose will decline
- Second vax (booster) needed to stimulate secondary response
- Memory cells react quickly to second exposure → higher, longer lasting level of antibodies
why should there be a time period between two vax shots?
Given too soon → antibodies present in blood will eliminate vaccine material before B-cells can be activated
herd immunity
occurs when high proportion of ppl in a population are immunised that those who aren’t immune are protected
social factors
- Ethical concerns with the use of animals to produce vaccines
- Ethical concerns with the use of human tissue to produce vaccines
- Ethical concerns with informed consent
- Ethical concerns with testing on animals
- Availability
Ethical concerns with the use of animals to produce vaccines
Viral vaccines require host tissue (as viruses can only be replicated in living cells)
Ethical concerns with the use of human tissue to produce vaccines
Using human tissue avoids problems of cross-species infection from possible unknown viruses
Ethical concerns with informed consent
Trialing vaccines in developing countries → use in populations with low standards of education → ppl aren’t fully aware of the risks → exploitation
Ethical concerns with testing on animals
- Prior to clinical trials in humans, vaccines tested on animals to identify potential
problems- Legislation exists to limit the way animals can be used
- Mice commonly uses
Availability
Vaccines aren’t always readily available in all areas
cultural beliefs
Religious beliefs
- Religious that rely on faith healing/healing through prayer
- Methods used to produce vaccines may contradict religious beliefs → non-participation in immunisation program
Economic factors
- Cost of vaccine
- May be too expensive
- Commercialisation
- Interests of commercial vaccine production may affect it’s use
antibiotics
Drugs used to fight infections of microorganisms eg. Bacteria
why can’t antibiotics be used to treat viral infections?
Viruses are not living cells → do not metabolise
types of antibiotics
- Bactericidal antibiotics
- Kill bacteria by
- changing the structure of the cell wall or membrane
- Disrupting action of essential enzymes
- Kill bacteria by
- Bacteriostatic antibiotics
- Stop bacteria from reproducing
- Disrupting protein synthesis
- Stop bacteria from reproducing
broad spectrum
Affects many types of bacteria
narrow spectrum
Effective only against specific types of bacteria
Antibiotic Resistance
Widespread use → some bacteria have evolved and become
resistant to antibiotics
- Multiple drug resistance = resistance of some strains of bacteria to most available antibiotics
- Caused by overuse of antibiotics in medicine and agriculture
How to slow this resistance
- Developing new classes of antibiotics
- Genetically engineer bacteria to disable antibiotic resistant genes
Antivirals
- Drugs used specifically to treat viral infections
- No treatment for common ailments such as colds, chickenpox
- The way viruses replicate makes it difficult to find drugs that will treat viral infections
- Host cell produces new virus particles, any drug that interferes with the virus replication is likely to be toxic to the host
- Research aimed at identifying viral proteins that can be disabled by specially designed chemicals
Recombinant DNA and vaccines - Hep B vaccine
- Gene for surface antigen on the virus is isolated → added to a plasmid
- Plasmid introduced into a yeast cell
- When yeast cell divides, new cells contain the plasmid with the gene for the antigen
- Gene allows the yeast cells to produce the antigen protein which can be collected and purified
