4.1.1 - Communicable Disease (set B - Defence Against Pathogens) Flashcards
Outline how plants are able to recognise an attack?
- receptors in the cell respond to molecules from pathogens or chemicals produced when cell wall is attacked
- stimulates release of signalling molecules that switch on genes in the nucleus
- triggers cellular responses - eg producing defensive chemicals/ sending alarm signals to unaffected cells to trigger defences or physically strengthens cell walls
Outline plants physical defences against pathogens - focus on callose?
produce high levels of callose (polysaccharide) when attacked - which is deposited between cell walls and membrane
callose acts as barrier preventing pathogen entering cells around infection site - lignin is added to further strengthen and thicken barrier
- callose blocks sieve plates in phloem - sealing of infected part, preventing spread (also deposited in plasmodesmata to stop spread)
Outline plants chemical defences against pathogens - give 4 and provide examples?
- insect repellents - eg pine resin
- insecticides - eg caffeine which is toxic to insects and fungi
- antibacterial compounds - eg phenols - which are antiseptics made in plants disrupt pathogen cell membranes
- general toxins - plants can make compounds that can be broken down to from cyanide compounds - toxic to living organisms
What are the two lines of defence mammals have against invasion by pathogens?
- the primary non-specific defense
- specific immune response (slower than non specific - up to 14 days but faster second invasion)
Outline the non-specific defences which keeps pathogens out?
- the skin
- mucous membranes
- lysozymes in tears and urine + acid in the stomach
Expulsive reflexes - eg coughing/sneezing/vomiting/diarrhoea - expels mucus containing pathogen or contents of the gut containing pathogens
Explain how the skin acts as a barrier preventing pathogens entering?
- skin covers the body, preventing entry of pathogens - has a flora of healthy microorganisms that outcompete pathogens for space on the body surface
- skin produces oily substance, sebum - which Inhibts pathogen growth
Explain how mucous membranes help keep pathogens out?
- airways of gas exchange systems are lined by mucous membranes which secrete sticky mucus (containing lysozymes and phagocytes) - trap microorganisms destroying bacterial and fungal cell walls
Explain how blood clotting and wound repair help prevent pathogens entering the body?
- when the skin is cut and breached - pathogens can enter the body
- when platelets come into contact with collagen in skin they adhere and secrete thromboplastin and serotonin
- clot dries out forming tough scab - starting process of wound repair
Explain how the substance thromboplastin is involved in wound repair?
- enzyme which triggers a cascade of reactions resulting in the formation of a blood clot
Explain how the substance seretonin is involved in wound repair?
- causes smooth muscle in the walls of the blood vessel to contract - so they narrow which reduces the supply of blood to the area
Explain how wound repair occurs?
- formation of scab - aided by secretion of thromboplastin and serotonin
- epidermal cells below scab start to grow - sealing wound permanently, damaged blood vessels regrow
- collagen fibres deposited to provide tissue strength
- scab sloughs off when the wound is healed
Outline the inflammatory response to pathogens?
- localised response - results in inflammation at the site of a wound
- mast cells are activated in damaged tissue - they release chemicals (histamines and cytokines)
Outline the chemicals involved in inflammatory response - histamines and cytokines?
Histamines - make blood vessels dilate - causing localised heat and redness - prevents pathogens reproducing
Histamines - make blood vessel walls more leaky so blood plasma is forced out - tissue fluid causes swelling and pain
Cytokines - attract phagocytes to site - which dispose of pathogens
Outline the non-specific defences which gets rid of pathogens?
- fevers
- phagocytosis
Explain how fevers help get rid of pathogens?
- cytokines stimulate hypothalamus causing temperature to increase
Pathogens reproduce best at or below 37 degrees - higher temps Inhibits pathogen reproduction
Specific immune system works faster at higher temperatures
Explain how phagocytosis can help get rid of pathogens?
- phagocytes are specialised WBC’s that engulf and destroy pathogens - two main types - neutrophils and macrophages
- build up at the site of an infection and attack pathogens
takes 10 minutes for neutrophil to engulf and destroy pathogen - macrophages take longer
Outline the stages of phagocytosis - and its involvement in getting rid of pathogens?
1) pathogens produce chemicals that attract phagocytes
2) phagocytes recognise non-human proteins (antigens) on pathogen as non-self and binds to it
3) phagocyte engulfs pathogen and encloses it in a vacuole called a phagosome
4) phagosome combines with a lysosome forming a phagolysosome
5) enzymes from lysosome digest and destroy the pathogen
6) digested pathogen absorbed by phagocyte-antigens combine with MHC in cytoplasm
7) MHC antigen complex displayed on phagocyte membrane - making an antigen presenting cell
stages 6 and 7 for macrophages
Explain how the stages of phagocytosis varies between neutrophils and macrophages?
- takes neutrophil 10 mins to engulf and destroy pathogen
- macrophages undergo a more complex process (stages 6 and 7) - macrophages combines glycoprotein (MHC) with antigens from digested pathogen - which moves to surface membrane becoming an antigen-presenting cell (APC) which stimulate other cells in specific immune system response
Explain the role of cytokines produced by phagocytes?
- act as cell-signalling molecules - informing other phagocytes that the body is under attack - stimulates them to move to the site of infection
- can also increase body temp, stimulating specific immune system
Explain the role of opsonins produced by phagocytes?
- chemicals that bind to pathogens - and ‘tag’ them - can be more easily recognised by phagocytes
- phagocytes have receptors on cell membranes that bind to opsonins
Outline the structure of antibodies?
- Y-shaped glycoproteins called immunoglobulins - bind to specific antigen on pathogen or toxin
- made up of 2 identical long polypeptide chains (heavy chains) and two much shorter identical chains (light chains) held together by disulphide bridges also disulphide bridges in polypeptide chains
- also have a hinge region - providing flexibility and allowing for binding to 2 separate antigens
- variable region different on different antibodies
Explain the role of the hinge region?
Provides the molecule with flexibility - allowing it to bind two separate antigens - one at each of its antigen-binding sites
Explain how antibodies bind to antigens?
- based on ‘lock and key’ mechanism - binding site on light and heavy chain known as variable region (makes antibody specific)
- rest of antibody same - constant region
Antibody blinds to antigen forming antigen-antibody complex - hinge region allows it to bind two separate antigens at each binding site
Outline how antibodies defend the body?
1) antibody of antigen-antibody complex acts as an opsonin (complex is easily engulfed by pathogen)
2) pathogens can no longer effectively invade host cells once they are part of an antigen-antibody complex
3) antibodies act as agglutinins causing pathogens carrying antigen-antibody to clump together - preventing spread
4) antibodies act as anti-toxins - binding to toxins produced by pathogens - making them harmless
Outline what’s involved in the specific immune system
Based on white blood cells (lymphocytes) B lymphocytes mature in bone marrow T lymphocytes mature in thymus gland
Both come from bone marrow
Outline the 4 main types of T lymphocytes?
- T helper cells
- T killer cells
- T memory cells
- T regulator cells
Explain what T helper cells are?
- have receptors on cell surface membrane which bind to surface antigens on antigen presenting cells
- produce interleukins - types of cytokine which stimulates activity of B cells (increasing antibody production and other T cells) and attracts and stimulates macrophages to ingest pathogens
Explain what T killer cells are?
- destroys pathogens carrying the antigen
- produce chemicals called perforin - kills the pathogen by making holes in the cell membrane so its permeable
Explain what T memory cells are?
- live for long time - part of immunological memory
- if they meet antigen second time they divide rapidly forming huge number of clones of T killer cells that destroy pathogens
Explain what T regulator cells are?
- cells suppress immune system, controlling and regulating it
- stop immune response once pathogen has been eliminated
- make sure body reorganise self antigens - and does not set up an autoimmune response
Explain the 3 main types of B lymphocytes?
- plasma cells
- B effector cells
- B memory cells
Explain what plasma cells are?
- produce antibodies to a particular antigen and release them into circulation
- only live for few days - produce 2000 antibodies per second
Explain what B effector cells are?
- divide to form the plasma cell clones
Explain what B memory cells are?
- live for very long time - providing immunological memory
- programmed to remember a specific antigen - gives the body a very rapid response when a pathogen carrying antigen is encountered again
What are the 2 systems of immunity?
- humoral immunity
- cell mediated immunity
Explain the need for counting blood cells?
Identifying the number of different types of lymphocytes in a blood smear indicates if a non-specific or specific immune response is taking place
- done by spreading a single drop of blood very thinly across a slide and staining it - to show nuclei of lymphocytes
Outline the process of cell-mediated immunity?
- macrophages engulf and digest pathogens (phagocytosis) - processing the antigen and forming antigen-presenting cells (APCs)
- receptors on T helper cells fit the antigens - which become activated and produced interleukins thus stimulating rapid division by mitosis of more clone T helper cells which carry right antigen to bind to particular pathogen
- clone T cells may develop into T memory cells (for rapid response in future), produce interleukins (to stimulate phagocytosis or B cells to divide) or stimulate development of a clone of T killer cells
Outline the process of humoral immunity
1) activated T helper cells bind to the B cell APC - clonal selection
2) interleukins produced by activated T helper cells activate the B cells
3) activated B cells divide by mitosis to give clones of plasma cells and B memory cells - clonal expansion
4) plasma cells produce antibodies that fit antigens on pathogens surface disabling them or acting as opsonins or agglutinins - primary immune response
5) some cloned B cells develop into B memory cells - which divide rapidly to form plasma cell clones during another infection - secondary immune repose
Explain the role of cell mediated immunity?
T lymphocytes response to the cells of an organism that have been changed in some way - eg by a virus, antigen processing or mutation (cancer)
Explain the role of humoral immunity?
Body responds to antigens found outside the cells (eg bacteria/fungi or APCs)
- produces antigen-specific antibodies
