The body and infection - Chapter 7 Flashcards
Pathogens
bacteria, virus, fungi and animal parasites.
How can a virus infect a person?
- infect a living cell and its DNA/RNA induces the cell to manufacture more virus particles
- new virus particles leave host cell and infect other cells
- during this, cells become damaged, change or die
Transmission of pathogens
- transmission by contact
- ingestion
- body fluids
- droplets
- airborne transmission
- vectors
Transmission by contact
physical contact (direct or indirect)
Transmission by ingestion
ingestion of food or drinks containing pathogens - salmonella or typhoid fever
Transfer by body fluids
transfer of body fluids from one person to another - when blood/body fluids of infected person comes in contact with an uninfected persons mucous membranes, infection may enter that person.
Transfer by droplets
infection by droplets of moisture - sneezing, coughing, talking etc (covid-19)
Transfer by air
airborne transmission - when moisture in exhaled droplets evaporates, many bacteria are killed, but some viruses and bacterium remain viable.
Transmission by vectors
transfer of pathogens by insects, ticks or mites.
non-specific defence
work against pathogens and are the first line of defence.
specific defence
are directed at a particular pathogen.
External defences
- skin
- mucous membranes
- hairs
- cilia
- acids
- lysozyme
- cerumen
- movement of fluid
Skin as a defence
in addition to the skin, it secretes sebum which is produced by oil glands in the skin (contains substances that kill pathogenic bacteria). sweat contains salts and fatty acids that prevent growth of many micro organisms.
Mucous membranes as a defence
line body cavities that open to exterior. they secrete mucous which traps particles, inhibiting the entry of micro-organisms. digestive, urinary and reproductive tracts are all lined this way.
Hairs as a defence
found in the nasal cavity, in the nose and in the ears.
Cilia as a defence
tiny hair projections from the cells that are capable of a beating motion. moves mucous, containing trapped particles and microorganisms to the throat where it may be coughed up or swallowed.
Acids as a defence
stomach juices are strongly acidic, killing most of the bacteria taken in with food and those contained within the mucous swallowed. vagina also has acidic secretions. urine and sweat are strongly acidic.
Lysozyme as a defence
is an enzyme that kills bacteria. tears contain this enzyme, protecting the eyes. saliva, sweat, secretions of the nose and tissue fluid all contain this enzyme.
Cerumen as a defence
aka ear wax protects the outer ear against infection by some bacteria. slightly acidic and contain lysozyme.
Movement of fluid as a defence
urine flowing through the urethra has a cleansing action, preventing bacterial growth and helps to stop bacteria reaching the bladder and kidneys.
Protetive reflexes
coughing, sneezing, vomiting, diarrhoea
Phagocytic cells
monocytes + macrophages, neutrophils and dendritic cells
Monocytes and macrophages
when tissues infected/inflamed, monocytes leave bloodstream and enter the tissue where they differentiate into macrophages. some macrophages look for and destroy pathogens in the tissue, others are fixed in one place and only deal with pathogens that come to them.
Neutrophils
descried as a granulated leucocyte, due to the granules in their cytoplasm. account for 55-70% of all leucocytes. during an infection, neutrophils are the first cells to move into tissue and destroy the pathogen. they are important in killing pathogens inside the cell. they die after a few days and make up a large part of the pus forming after an infection.
Dendritic cells
characterised by projections from the cytoplasm. they have ability to detect, engulf and process foreign particles, then using information from ingested particles to assist with specific immunity.
Steps of the inflammatory response
- mechanical damage causes mast cells to be activated by compliment proteins. this results in the release of histamine, heparin and other chemicals into the tissue.
- histamine increases blood flow through the area due to vasodilation, making blood capillary walls more permeable. more fluid moves through capillary walls into the tissue. increased blood flow causes heat and redness, and escape of fluid from blood causes swelling.
- heparin prevents blood clotting. a clot of fluid forms around the damaged area, which slows the spread of pathogen into healthy tissues.
- complimentary proteins attract phagocytes which actively consume micro-organisms and debris by phagocytosis.
- the abnormal condition in the tissue stimulates pain receptors, so the person feels pain in the inflamed area.
- phagocytes begin to die, forming pus.
- new cells are formed by mitosis and the repair of the damaged tissues takes place.
Fever
an elevation of body temperature above normal level of 37º
- it is due to pyrogens that are released by wbc’s during inflammatory response, acting on hypothalamus and resetting bodies thermostat.
- one pyrogen is interleukin-1
- bodies thermoreceptors detect body temp, hypothalamus recognises it is lower than the new, higher set point. as consequence, vasoconstriction of skin and shivering occurs.
- both these activities conserve heat and increase heat production, driving body temp up rapidly.
- death will result if body temp reaches 44.4-45.5ºC.
What does high body temperature inhibit?
the growth of some bacteria and viruses.
however, heat speeds up the rate of chemical reactions which may help body cells repair themselves more quickly during a disease.
What does the lymphatic system consist of?
- a network of lymph capillaries joined to larger lymph vessels
- lymph nodes, which are located along the length of some lymph vessels
Function of the lymphatic system
collect some of the fluid the escapes from the blood capillaries and return it to the circulatory system. also is an important part of the body’s internal defence against pathogenic organisms.
What occurs in lymphatic system when infections occur?
formation of the lymphocytes increases, and the lymph nodes become swollen and sore.
Types of immune response
- humoral response/ antibody-mediated immunity
- cell-mediated response
Humoral response (antibody-mediated immunity)
involves the production of special proteins called antibody B-cells, which circulate around the body and attack invading agents.
Cell-mediated response
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.
they’re large molecules such as proteins, carbohydrates, lipids and nucleic acids. may include:
- virus particles
- toxins
- part of bacterium
Self-antigen
a large molecule produced in a persons own body; does not cause an immune response in that person.
Non-self antigen
any compound foreign to the body that triggers an immune response.
Antibodies
a y-shaped specialised protein produced in response to a specific antigen, combining with the antigen to neutralise and destroy it.
- belong to a group of proteins called immunoglobulins
Antigen-antibody complex
is a compound formed when an antibody combines with an antigen.
- antigens have specific active sites with a particular shape
- the antibody has the complimentary shape, allowing the two molecules to fit together like a lock and key.
Antigen-presenting cells
phagocytic cells that:
- detect the presence of a non-self antigen
- engulf the pathogen
- digest the pathogen, producing small fragments that move to the surface of the cell
- present the antigen to lymphocytes
Antibody-mediated immunity
- when an antigen presenting cell presents antigen to specific B-cell, B-cells are activated. it is also presented to helper T-cells leading to the release fo cytokines.
- cytokines cause the helper T-cells to clone themselves to release different cytokines, which a activates the B-cells.
- activated B-cells enlarge and divide into a group of cells called clones.
- most clones become plasma cells - they secrete antibodies which circulate the blood, lymph and extracellular fluid to reach site of the invasion of microorganisms or foreign material.
- remaining B-cells of clone become memory cells - which spread to all body tissues to allow the response to occur more rapidly should the antigen enter the body again.
3 Examples of how antibodies work
- they bind to the surface of viruses and prevent them entering cells
- coat bacteria so theyre more easily consumed by phagocytes
- cause particles such as bacteria, viruses or foreign blood cells to clump together (agglutination)
Cell-mediated immunity
- when a foreign antigen (virus/bacterium) enters the body, antigen-presenting cells present the antigen to the particular type of T-cells - becoming activated/sensitised
- sensitised T-cells enlarge and divide, each giving rise to a clone
- some cells of the clone remain in lymphoid tissue as memory cells.
- the T-cells that do not become memory cells develop further, producing three different types of T-cells: Killer T-cells, Helper T-cells and Suppressor T-cells.
Killer T-cells
(cytotoxic T-cells) attach to invading cells and secrete a chemical that will destroy the antigen, and then go in search of more antigens.
Helper T-cells
bind to the antigen on antigen presenting cells, stimulating the secretion of cytokines that:
- attract lymphocytes to the infection site which sensitise and activate, intensifying the response
- attract macrophages to infection site so they can destroy antigens by phagocytosis
- intensify the phagocytic activity of macrophages
- promote the action of Killer T-cells
Suppressor T-cells
when immune activity becomes excessive or infection dealt with successfully, they release substances that inhibit T- and B-cell activity, slowing down the immune response.
Immunity
resistance to infection by invading microorganisms
Passive (natural) immunity
antibodies enter the blood stream across the placenta or in breast milk.
Passive (artificial) immunity
antibodies are injected into the blood stream
Active (natural) immunity
ability to manufacture antibodies results from an attack of a disease.
Active (artificial) immunity
ability to manufacture antibodies results from being given an antigen by vaccination.
Antibiotics
drugs that are used to fight infections of micro-organisms, particularly bacteria.
- each only effective for certain types of bacteria.
*first antibiotic = penicillin
Why have the effects of penicillin reduced?
because many bacteria have developed resistance to it. 10% of people are allergic to penicillin
Bactericidal antibiotics
kill bacteria by changing the structure of the cell wall or cell membrane, or by disrupting the action of essential enzymes.
Bacteriostatic antibiotics
stop bacteria from reproducing, usually by disrupting protein synthesis.
Multiple drug resistance
some strains of bacteria being resistant to almost all available antibiotics.
Total drug resistance
some strains of bacteria resistant to all antibiotics.
Antivirals
used specifically for treating viral infections.
