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Topic 6.3 Defence against infectious disease Topic 6: Human Health and Physiology.

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Presentation on theme: "Topic 6.3 Defence against infectious disease Topic 6: Human Health and Physiology."— Presentation transcript:

1 Topic 6.3 Defence against infectious disease Topic 6: Human Health and Physiology

2 A pathogen in an organism or virus that causes disease. Some diseases are caused by genetic defects, others by environmental stresses – not all diseases are infections.

3 What 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?

4 Characteristics of living things Properties of life Cellular Respiration Reproduction Metabolism Homeostasis Heredity Responsiveness Growth and development

5 Viruses infecting living cells

6 Viruses are not living organisms Viruses do not Grow Have homeostasis Metabolize Viruses do Infect cells and use the cell to make more viruses Cause disease in many organisms

7 Viruses Viruses are micro organisms consisting of a strand of DNA or RNA surrounded by a protein coat They enter cells and hijack the cells machinery to make more viruses. They then burst out of the host cell, destroying or damaging it.

8 Other pathogens Bacteria Fungi Protozoa Animals Prions

9 Flip over to I-biology ppt

10 Antibiotics Major medical improvement Produced by fungi and bacteria Work on bacteria but… Cannot be used on viruses antibiotics block specific metabolic pathways found in bacteria, but not eukaryotic cells because viruses reproduce using the host cell (eukaryotic) metabolic pathways, they are unaffected by antibiotics antibiotics have produced great benefits world-wide in the control of bacterial diseases Staphylococcus infections controlled STD's, such as gonorrhea and syphilis controlled antibiotic resistance has evolved in bacterial populations


12 In what form can pathogens enter the body?

13 6.3.3 Outline the role of skin and mucous membranes in defence against pathogens

14 Skin Unbroken skin provides a fantastic barrier against pathogens trying to enter the body Sebum (oil) waterproofing You do not need to learn the parts of this diagram.

15 Mucous Membranes (and other non-specific immunity) Lungs – Mucous membranes and cilia Stomach – Acid Urethra – mucus membranes + urine is sterile Eyes – tears contain lysozymes Vagina – mucous membranes and acid Anus – mucous membranes Anywhere on the body that is not protected by skin has its own method of protection.


17 Infection! 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.

18 Phagocytosis

19 Phagocytes Phagocytes 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.

20 Phagocytosis

21 damage to tissues allows invasion across 1st line of defense microbes successfully invade body fluids or tissues damaged cells release histamine and other chemicals initiating inflammation phagocytes attracted to site by chemotaxis toward histamine phagocytes recognize microbes as foreign by antigen recognition variety of phagocytic cells: neutrophils (small phagocytic & macrophages (large phagocytic) phagocytes endocytotically engulf microbes,which are digested by enzymes held in lysosomes digested microbe fragments are displayed on cell membrane phagocytes with microbe fragments displayed = antigen- presenting cells


23 antigens and antibodies antigens and antibodies antigen: a molecule recognized as foreign by the immune system; it elicits an immune response; usually a foreign protien antibody: =immunoglobulin a globular glycoprotein recognizes an antigen by its complementary shape and charge thus allowing it to attach to the antigen specifically marking it for attack by the immune system

24 Antibodies Also known as immunoglobulins Globular glycoproteins The heavy and light chains are polypeptides The chains are held together by disulphide bridges Each 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

25 How Antibodies work? Some act as labels to identify antigens for phagocytes Some work as antitoxins i.e. they block toxins for e.g. those causing diphtheria and tetanus Some attach to bacterial flagella making them less active and easier for phagocytes to engulf Some cause agglutination (clumping together) of bacteria making them less likely to spread

26 TypeNumber of ag binding sites Site of actionFunctions IgG2 Blood Tissue fluid CAN CROSS PLACENTA Increase macrophage activity Antitoxins Agglutination IgM10 Blood Tissue fluid Agglutination IgA2 or 4 Secretions (saliva, tears, small intestine, vaginal, prostate, nasal, breast milk) Stop bacteria adhering to host cells Prevents bacteria forming colonies on mucous membranes IgE2Tissues Activate mast cells  HISTAMINE Worm response

27 Lymphocyte with antigens


29 Blood types

30 Where do antibodies come from?= Lymphocytes Produce antibodies B-cells mature in bone marrow then concentrate in lymph nodes and spleen T-cells mature in thymus B and T cells mature then circulate in the blood and lymph Circulation ensures they come into contact with pathogens and each other

31 White Blood cells WBC (Lymphocytes) are made in the bone marrow. The cells divide and mature into 2 types: T Lymphocytes B Lymphocytes Develop in the thymus gland Develop in the bone marrow  lymph nodes Plasma 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 a pathogen. 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. The Humoral (Antibody) ResponseThe Cell-Mediated Resopnse Foreign, mutant or infected cells are identified as ‘non-self’ by surface antigens. T helper cell recognises antigens and alerts the other T cells. Killer (Cytotoxic) cells attack with perforin or nitric oxide. T memory cells remember the antigen for a later attack. T suppressor cells switch off T and B cells after attack over.

32 HIV HIV is a virus that specifically attacks the T lymphocytes. This means the number of lymphocytes decreases. Less antibodies are made. Predict the consequences…








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