10. Protection against infection Flashcards
What are communicable diseases?
Diseases that are caused by foreign organisms invading the body and multiplying
What are pathogens?
Disease causing organisms
What does it mean if a disease is contagious?
It means the disease is passed on by diret contact with a person suffering the disease, or by contact with something touched by the person
What are vectors?
They are intermediate hosts of the pathogen (mosquitos or fleas)
Are the majority of bacteria, pathogenic or non-pathogenic
Non-pathogenic, meaning they live in our skin, alimentary canal or in the body
How are bacteria classified?
They all consist of a single cell and are classified according to their shape
Describe the structure of a bacteria cell:
- Slime layer around the outside of some bacteria
- Cell wall: composition varies but are often made of peptidoglycan
- Cell membrane is similar to other cells
- No nuclear membrane, DNA forms a tangle inside the cell, some in loops
- May have flagella for movement
- Cytoplasm appears granular due to the presence of ribosomes
- No membrane-bound organelles
- Capsule formed of complex carbohydrates in some for protection
What are the different types of bacterial cell types?
Cocci, Bacilli, Spirilla, Vibrio
What are Cocci?
Spherical cells, may occur single, in pairs (diplococci), in clusters (staphylococci) or in chains (streptococci)
What are bacilli?
Rod shaped cells with flagella
What are spirilla?
Twisted cells
What are Vibrio?
curved rods, shaped like a comma
What are viruses?
Structures too small to be seen under a light microscope, single celled organisms able to multiply within a host
What are distinctive structures in viruses?
All viruses have genetic material in either DNA or RNA form, never both
This genetic material was surrounded by a protein coat
Some viruses have an additional envelope of lipid or protein molecules
What happens when a virus infects a living cell?
Its DNA or RNA induced the cell to manufacture more virus particles
These then are able to infect other cells
What are bacteriophages?
Viruses that are able to multiply in bacterial cells which can cause the death of the bacterium
Are all viruses bad?
No, not all are harmful and they can even be used to insert new genes into other organisms
What are the different types of transmissions of a pathogen?
Transmission by contact Transmission of bodily fluids Infection of droplets Ingestion Airborne transmission Transmission by vector
How is a pathogen transmitted by contact?
- Contact may be direct (touching an infected person)
- Indirect: touching an object that has been touched by an infected individual
- Skin infections and STI’s are spread by contact
How is a pathogen transmitted via bodily fluids?
- Blood or bodily fluids can come into contact with the mucous membrane (nose, mouth, throat, genitals) or bloodstream of an uninfected person
- Through a needle stick, break in the skin, or unprotected sex
- Pathogens may enter the body of the person
- HIV, Hepatitis B and C
How is a pathogen transmitted by droplets?
- tiny droplets of moisture, harbouring pathogenic organisms are emitted when breathing, tlakimg, sneezing and coughing
- Droplets may be breathed in by others, or may settle on food or utensils and be ingested with food
- Viral infections are often spread this way- measles, mumps, colds, influenza
How are pathogens transmitted through ingestion?
- Taking in food or drink contaminated by pathogens
- Dysentery, typhoid fever, salmonella
How is a pathogen transmitted via air?
- When the moisture in exhaled droplets evaporates, many bacteria are killed, but some remain viable
How is a pathogen transmitted via vectors?
- Transmission of pathogens by animals, like insects, ticks or mites
- Some transfer the pathogen directly, others (house flies) may spread it to food or water which is then ingested
- Vector-borne diseases are often spread by a specific vector- malaria and dengue fever are spread by mosquitos, lyme disease by ticks etc.
What is a non-specific defence?
Work against all pathogens, the ‘first line of defence’
What is a specific defence?
A defence directed at a particular pathogen
What are the bodies external, non-specific defences?
Skin Mucous membranes Hair Cilia Acids Lysozyme Cerumen Body fluids
How is skin an external non-specific defence?
- effective barrier covering the outside of the body
- Stops the entry of micro-organisms, provided it’s not broken by cuts or abrasions
- huge numbers of bacteria live on the skin at all times- preventing other bacteria from becoming established
- sebum contains substances to kill some pathogenic bacteria
- sweat contains salts and fatty acids to prevent the growth of microorganisms
How are mucous membranes an external non-specific defence?
- line body cavities that open to the exterior
- secrete mucous, which inhibits the entry of micro-organisms to body organs
- digestive, urinary and reproductive tracts are protected
How is hair an external non-specific defence?
- in the nose cavity and ears
- along with mucous/wax, trap up to 90% of particles
How is cilia an external non-specific defence?
- tiny hair like projections from cells that are capable of a beating motion
- mucous membranes of the nose cavity, trachea and air passages have cilia
- beating of cilia moves mucous towards the throat, where they are coughed or swallowed
How are acids an external non-specific defence?
- stomach juices are strongly acidic which kills many of the bacteria taken in with food or those contained in the mucous from the nose and windpipe
- The vagina has acid secretions that reduce micro-organism growth
- sweat is also slightly acidic
How is lysozyme an external non-specific defence?
- an enzyme that kills bacteria
- eyes are protected by the tears, which contain this enzyme
- also found in saliva, sweat, secretions of the nose and tissue fluid
How is cerumen an external non-specific defence?
- ear wax protects the outer ear against bacterial infection
- slightly acidic and contains lysozyme
How are body fluids an external non-specific defence?
- flushing action of the body fluids helps keep some areas relatively free of pathogens
- urine flowing through the urethras has a cleansing action, which prevents bacterial growth
- women have shorter urethras so tend to suffer more from bladder infections
- tears, sweat, and saliva are also involved in flushing and cleansing
What are 4 protective reflexes that help protect against infection?
sneezing
coughing
vomiting
diarrhoea
How is sneezing a protective reflex against infection?
- stimulus for sneezing is irritation of the walls of the nasal cavity
- Irritation may be caused by noxious fumes or dust particles which are likely to be carrying micro-organisms
- forceful expulsion of air from the lungs causes mucus, foreign particles ad irritating gases out through the nose and mouth
How is coughing a protective reflex against infection?
- stimulus for coughing is irritation in the lower respiratory tract (bronchi/bronchioles)
- Air is forced from the lungs to try remove the irritant
- air drives foreign matter up the trachea towards the throat and mouth
How is vomiting a protective reflex against infection?
- psychological stimuli, excessive stretching of the stomach, and bacterial toxins can all induce vomiting
- not a contraction of the stomach, but a contraction of the muscles of the abdomen and the diaphragm that expel the stomach contents
How is diarrhoea a protective reflex against infection?
- irritation of the small and large intestines by bacteria, viruses or protozoans
- irritation causes increased contractions of the muscles of the wall of the intestines so the irritant is removed as quickly as possible
- material does not stay in the large intestine long enough for water to be absorbed so faeces are very watery
What are internal non-specific defences?
Phagocytes:
- leucocytes
- macrophages
What are phagocytes?
Cells that engulf and digest micro-organisms and cell debris
What are leucocytes and how are the internal non-specific defences?
- white blood cells
- able to leave blood capillaries and migrate through the tissue to places of infection or injury
- some secrete substances that destroy the bacteria before engulfing the
- some engulf live bacteria and digest them
What are macrophages and how are the internal non-specific defences?
- large phagocytic cells that develop from some leucocytes
- some move through tissues looking for pathogens
- others fixed in one place and only deal with pathogens that cross its path
- either engulf or digest micro-organisms, or release substances to destroy them
- often eliminate pathogens before an infection can take hold
What are the steps to an inflammatory response?
- cell stimulated by mechanical damage or local chemical changes
- Mast cells release histamine, heparin, and other substances into the tissue fluid
- These chemicals attract phagocytes, which consume micro-organisms and debris
- Abnormal tissue conditions stimulate pain receptors, so pain is felt in the inflamed area
- The phagocytes begin to die- forms a yellow liquid with the tissue fluid (pus)
- new cells are reproduced by mitosis, repair of damaged tissue takes place
What are mast cells?
Cells that are present in most tissues, stimulate and coordinate inflammation by releasing chemicals
What is inflammation?
a response to any damage of the tissues in order to reduce the spread of pathogens, destroy them, prevent the entry of additional pathogens, remove damaged tissue and cell debris and begin the repair of damaged tissue
What are the four key signs of inflammation?
redness, swelling, heat and pain
What does histamine do?
- increases blood flow to an area
- causes the walls of the blood capillaries to become more permeable so more fluid is filtered from the blood
- increased blood flow causes the heat and redness, escape of fluid causes swelling
What does heparin do?
- Prevents clotting in the immediate area or injury
- a clot of the fluid around the damaged area does still form, which slows the spread of pathogen into healthy tissues
What is a fever?
An elevation of body temperature due to heat regulation
Why does a person feel cold when they have a fever?
- person feels cold and vasoconstriction and shivering occur to conserve heat and raise internal temperature
- when fever breaks, the person feels hot and vasodilation and profuse sweating occur
Why is a fever beneficial?
to a point
- high body temps are believed to inhibit the growth of some bacteria and viruses
- increases the rate of chemical reactions which can help the body repair faster
- fever can be harmful if too high
What is the main function of the lymphatic system?
to collect fluid from blood capillaries and return it to the circulatory system
also aids in non-specific defence
How is the lymphatic system a defence?
- lymph entering nodes contain cell debris, foreign particles and micro-organisms
- particles get trapped in the masses of lymphoid tissue inside lymph vessels
- macrophages destroy the particles, ingesting them by phagocytosis
- most bacteria killed within 10-30 minutes
what happens to the lymphatic system during infection?
-lymphocyte formation increases and the lymph nodes become swollen and sore
What are behavioural and mechanical steps that can reduce risk of pathogen infection?
- wash hands
- cover mouth when coughing or sneezing
- wear gloves when cleaning bodily fluids
- wipe surfaces with disinfectant if contaminated
- use tongs, pliers or tweezers when picking up discarded contaminated items
- never share toothbrush/razor/etc
- wear surgical masks in the presence of those who are sick
