Presentation on theme: "Topic 6.3 Defence against infectious disease"— Presentation transcript:
1Topic 6.3 Defence against infectious disease Topic 6: Human Health and Physiology
2What is a pathogen? Patho = disease Gen = Producer A pathogen is an organism or virus that causes a disease.Why aren’t viruses called organisms??Organisms are living things. What are the characteristics of living things?
3Characteristics of living things Properties of lifeCellular RespirationReproductionMetabolismHomeostasisHeredityResponsivenessGrowth and development
5Viruses are not living organisms Viruses do notGrowHave homeostasisMetabolizeViruses doInfect cells and use the cell to make more virusesCause disease in many organisms
6VirusesViruses are micro organisms consisting of a strand of DNA or RNA surrounded by a protein coatThey enter cells and hijack the cells machinery to make more viruses.They then burst out of the host cell, destroying or damaging it.
7Other pathogens Bacteria Fungi Protozoa Animals Prions Bacteria – single celled organisms able to reproduce by themselves. Categorised based on their shape.Protozoa (larger and more complex than bacteria)Animals (e.g. flatworms, round worms)Prions are misformed proteins that get into organisms and cause cells to die, especially brain cells- ‘mad cow disease’, CJD in humans
8Antibiotics Major medical improvement Produced by fungi and bacteria Work on bacteria but…Cannot be used on virusesantibiotics block specific metabolic pathways found in bacteria, but not eukaryotic cellsbecause viruses reproduce using the host cell (eukaryotic) metabolic pathways, they are unaffected by antibioticsantibiotics have produced great benefits world-wide in the control of bacterial diseasesStaphylococcus infections controlledSTD's, such as gonorrhea and syphilis controlledantibiotic resistance has evolved in bacterial populationsOne of the most major advances in modern medicine has been the development of AntibioticsProduced by fungi and bacteria to inhibit growth of their competitors
9Non specific immunityThe body resists infection with general (non-specific) and specific methods.Non-specific immunity stops a wide variety of pathogens.
12SkinUnbroken skin provides a fantastic barrier against pathogens trying to enter the bodySebum (oil) waterproofingYou do not need to learn the parts of this diagram.
13Mucous Membranes (and other non-specific immunity) Anywhere on the body that is not protected by skin has its own method of protection.Eyes – tears contain lysozymesVagina – mucous membranes and acidAnus – mucous membranesLungs – Mucous membranes and ciliaStomach – AcidUrethra – mucus membranes + urine is sterileMucous membranes secrete a physical barrier of mucus which traps pathogens. The mucus is then swept out of the throat and nose and into the stomach.Mucus is antiseptic (kills bacteria) due to lysozymesLysozymes – destroy bacterial walls
14Infection! This occurs if pathogens do get inside the body. The proteins on the surface of a pathogen are immediately recognised as “foreign”.Phagocytes (a type of leucocytes) will ingest the pathogen by phagocytosis.
15Blood Clotting HLClotting is the mechanism that prevents and blood lossfrom broken blood vessels.MechanismPlatelets or damaged cells release a group of proteinscalled clotting factors. These clotting factors are releasedinto the plasma a wound site.b) Clotting factors activate the enzyme Thrombin fromits inactive form prothrombinc) Thrombin turns the soluble plasma protein fibrinogeninto its insoluble fibrous form Fibrin.d) Fibrin binds together platelets and blood cells to forma solid 'plug' for the4 wound. This plug is called a clot.Damaged cells release an enzyme called Thrombokinase.This as well as Factor X, Factor VII and Ca+ inos cause Prothrombin (inactive enzyme) to change to Thrombin (active enzyme)Thrombin will hydrolyse soluble fibrinogen into fibrin which is insoluble.Fibrin forms a network which traps erythrocytes and becomes a clot.Anti haemophilia factors are VIII and IX – these are important in step a above.
19PhagocytesPhagocytes are found in the blood and in body tissues such as the lungs.After phagocytes engulf pathogens, they destroy them with digestive enzymes found in lysosomes.
20damage to tissues allows invasion across 1st line of defense microbes successfully invade body fluids or tissuesdamaged cells release histamine and other chemicals initiating inflammationphagocytes attracted to site by chemotaxis toward histaminephagocytes recognize microbes as foreign by antigen recognitionvariety of phagocytic cells: neutrophils (small phagocytic & macrophages (large phagocytic)phagocytes endocytotically engulf microbes,which are digested by enzymes held in lysosomesdigested microbe fragments are displayed on cell membranephagocytes with microbe fragments displayed = antigen-presenting cells
23PhagocytosisThis animation is in too much detail for SL IB but it shows the process perfectly!
246.3.5 Distinguish between antigens and antibodies SL antigen: a molecule recognized as foreign by the immune system; it elicits an immune responseantibody: =immunoglobulina globular proteinrecognizes an antigen by its complementary shape and chargethus allowing it to attach to the antigen specificallymarking it for attack by the immune system
25Antigens Anything that elicits an immune response Usually a foreign proteinA cat and its dander, an allergen/antigen for many people25
26Antibodies SL Also known as immunoglobulins Globular glycoproteins The heavy and light chains are polypeptidesThe chains are held together by disulphide bridgesEach antiboby has 2 identical antigen binding sites – variable regions.The order of amino acids in the variable region determines the shape of the binding site
27HL Challenge and response AntigensMost are proteins or large polysaccharides from a foreign organism.Microbes: Capsules, cell walls, toxins, viral capsids, flagella, etc.Nonmicrobes: Pollen, egg white , red blood cell surface molecules, serum proteins, and surface molecules from transplanted tissue.Lipids and nucleic acids are only antigenic when combined with proteins or polysaccharides.HL Challenge and responseChallenge:antigens:substances foreign to the hostwhich stimulate antibody production by B lymphocytesResponse:antibodies:immunoglobulinsproduced during protein synthesis
28How Antibodies work? Some act as labels to identify antigens for phagocytesSome work as antitoxins i.e. they block toxins for e.g. those causing diphtheria and tetanusSome attach to bacterial flagella making them less active and easier for phagocytes to engulfSome cause agglutination (clumping together) of bacteria making them less likely to spread
29Number of ag binding sites Site of action Functions TypeNumber of ag binding sitesSite of actionFunctionsIgG2BloodTissue fluidCAN CROSS PLACENTAIncrease macrophage activityAntitoxinsAgglutinationIgM10IgA2 or 4Secretions (saliva, tears, small intestine, vaginal, prostate, nasal, breast milk)Stop bacteria adhering to host cellsPrevents bacteria forming colonies on mucous membranesIgETissuesActivate mast cells HISTAMINEWorm response
30Antibodies are actively released by lymphocytes when the bodyis infected by a pathogen. This is a natural process.The lymphocytes are activated by the antigen on the pathogens outer surface.HL- A vaccine can also be artificially injected into the body. Advantages/Disadvantages?
32HL: To Vaccinate or not? Vaccines: MMR = combined measles/mumps/rubellaDPT = diphtheria, pertussis, typhoidpolioBenefits:eradication of some diseases (e.g. small pox)reduced rate of infection; less illness and deathreduced long-term disabilityDangers:low percentage of vaccinations produce side effects, including symptoms of disease, sometimes serious or lethalartificial immunity not as effective at producing immune response as is active immunityexcessive vaccination may reduce the ability of the immune system to respond to new diseasesvaccination possibly implicated in autism
34Active vs. Passive Immunity Active immunity: immunity acquired through individual immune responseCatching a diseasePassive immunity: immunity acquired through antibodies transferred from one person to anotherMother’s milk
35HL: Active and passive immunity However, it takes time for the body to react to the infection and produce white (B and T) cells. During this time the disease can multiply and spread rapidly.Tetanus is an especially deadly disease thatcan kill in hours. Antibodies can becollected from people who have already been vaccinated against it. These can then be injected into people who may have caught the infection. Its only a temporary fix- the spleen and liver break them down. This is Passive Immunity.Mothers pass antibodies through the placentaduring gestation. Colostrum is a liquid madein the mammary glands during the first fewdays after birth- it lines the gut and protectsagainst bacteria and viruses.
36HL Where do antibodies come from?= Lymphocytes Produce antibodiesB-cells mature in bone marrow then concentrate in lymph nodes and spleenT-cells mature in thymusB and T cells mature then circulate in the blood and lymphCirculation ensures they come into contact with pathogens and each other
37HL White Blood cellsWBC (Lymphocytes) are made in the bone marrow. The cells divide and mature into 2 types:T Lymphocytes B LymphocytesDevelop in the thymus gland Develop in the lymph nodesThe Cell-Mediated ResopnseThe Humoral (Antibody) ResponsePlasma ɞ cells have a different shape receptor on its membrane. There are about 10 million kinds in your body at any one time! Each can detect any antigen of apathogen. Once activated they divide very fast (clone) and start to secrete specific antibodies. Antibodies slowly removed from blood and lymph. Memory ɞ cells remember antigens and can turn into Plasma ɞ if re-infected.Foreign, mutant or infected cells areidentified as ‘non-self’ by surface antigens.T helper cell recognises antigens andalerts the other T cells.Killer (Cytotoxic) cells attack with perforinor nitric oxide. T memory cells rememberthe antigen for a later attack.T suppressor cells switch off T and B cellsafter attack over.
39How Do B Cells Produce Antibodies? B cells develop from stem cells in the bone marrow of adults (liver of fetuses).After maturation B cells migrate to lymphoid organs (lymph node or spleen).Clonal Selection: When a B cell encounters an antigen it recognizes, it is stimulated and divides into many clones called plasma cells, which actively secrete antibodies.Each B cell produces antibodies that will recognize only one antigenic determinant.
40B -LymphocytesChallenged and ResponseThe antibodies travel to the blood, lymph, lining of gut and lungs.The number of plasma cells goes down after a few weeksAntibodies stay in the blood longer but eventually their numbers go down too
41Clonal Selection of B Cells is Caused by Antigenic Stimulation
42Duality of Immune System I. Humoral (Antibody-Mediated) ImmunityInvolves production of antibodies against foreign antigens.Antibodies are produced by a subset of lymphocytes called B cells.B cells that are stimulated will actively secrete antibodies and are called plasma cells.Antibodies are found in extracellular fluids (blood plasma, lymph, mucus, etc.) and the surface of B cells.Defense against bacteria, bacterial toxins, and viruses that circulate freely in body fluids, before they enter cells.Also cause certain reactions against transplanted tissue.
43Immunological Memory Secondary Response: Subsequent exposure to the same antigen displays a faster and more intense antibody response.Increased antibody response is due to the existence of memory cells, which rapidly produce plasma cells upon antigen stimulation.Booster shots increase the number of memory cells
44HL Production of monoclonal antibodies Extract B cell that can produce the required antibodiesHybridise with a tumour cell (capable of endless division)In culture the hybridoma can produce large quantities of antibodies
45Production of monoclonal antibodies and their use Use in diagnosis – will be covered in (pregnancy diagnostic)TreatmentDiagnosis: HIV infection can be diagnosed through a blood testwhich assays for the presence of anti-HIV antibodies,antibody produced through monoclonal antibody production is an anti-anti-HIV antibody!Treatment:Rabies Virusmonoclonal antibodies can be produced which selectively locate and adhere to cancer cellsanti-cancer drugs can be attached to the monoclonal antibodiesso that they deliver their effects directly to the targeted cancer cells
46Immune System Abnormalities Allergies:Exaggerated immune response to antigens called allergensAutoimmune diseases:Body doesn’t recognize “self” and mounts immune response
47HIV HIV is a virus that specifically attacks the lymphocytes. This means the number of lymphocytes decreases.Less antibodies are made.Predict the consequences…Click here for a complex video on how the virus enters the lymphocyte
48Transmission of HIVYou should know this from IGCSE! You tell me!!
49Transmission of HIVInfected blood – blood transfusions, sharing needles,Infected semen and vaginal mucus – unprotected sexInfected mother’s milk – low riskInfected saliva – almost zero risk
50AIDS Acquired Immuno-Deficiency Syndrome Caused by the HIV virus that selectively infects the immune system leaving the body open to infection by removing the specific immunity.AIDS: Acquired Immuno deficiency syndrome.Acquired relates the infectious nature of AIDS through the transmission of the HIV virus.Immuno deficient relates to the way diseases cannot be resisted.Syndrome relates to the variation in the way the disease manifest itself. People who develop AIDS can be a affected by quite different set of diseases.
52Social implications of AIDS TOKSocial implications of AIDSThe social implications of AIDS are well known.Cases of AIDS are not evenly distributed in the world for example there are severe problems in southern Africa.What cultural and economic reasons are there for differences in the prevalence of AIDS?Is there a moral obligation of those with the technology and the wealth to help others lacking these things in the fight against AIDS?
53Social implications of AIDS Homework:Read the article “AIDS takes an economic and Social toll”.Highlight the key points.Read P103 in your text bookMake notes on the key points.