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TOPIC 6.3 Defence Against Infectious Disease Chapter 24.

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1 TOPIC 6.3 Defence Against Infectious Disease Chapter 24

2 6.3.1 Define pathogen. An organism or virus that causes a disease Types = viruses, fungi, bacteria, protozoa and worms of various types


4 6.3.2 Antibiotics are effective against bacteria, but not viruses Antibiotics are chemicals that work against living bacterial cells, but do not affect our body cells Bacteria are prokaryotic, body cells are eukaryotic – Different biochemical rxs and pathways – Protein synthesis not exactly the same – Bacteria have a cell wall, body cells don’t Many types of antibiotics – One type blocks protein synthesis in bacteria – Another type inhibits cell wall production so they can’t grow and divide

5 Antibiotics have no effect on viruses Antibiotics disrupt metabolism in bacteria Viruses make use of our body cells’ metabolism to create new viruses Viruses have no metabolism of their own Any chemical that would inhibit this would damage our body cells Antibiotics are chemicals with the ability to damage or kill prokaryotic cells, but not eukaryotic cells or their metabolism

6 Antibiotics Availability varies widely in various parts of the world Some places infections from bacteria are devastating, whereas people in other areas barely give these infections a second thought Overuse of antibiotics has led to strains that are resistant to many antibiotics



9 6.3.3 Role of skin and mucous membranes Skin is a barrier to infection – 2 primary layers: dermis and epidermis – Under layer is the dermis which contains sweat glands, capillaries, sensory receptors and dermal cells that give structure and strength to the skin – Top layer is the epidermis which is constantly replaced as dermal cells die and move upwards. These dead cells are a good barrier and prevent pathogens from entering living tissue. It is important to cleanse and cover cuts and abrasions.


11 Stomach acid When pathogens enter the body in food and water the acidic environment in the stomach helps to kill most of these ingested pathogens.

12 Mucus Pathogens may enter in the air we breathe through the nasal passage or mouth This route of entry is lined with tissue known as mucous membrane Area with mucous membrane What it is and does Trachea Tube which carries air to & from lungs Nasal passages Tubes which allow air to enter the nose and then the trachea urethra Tube which carries urine from bladder to the outside vagina Reproductive tract leading from uterus to the outside

13 Mucous Membranes Produce and secrete a lining of sticky mucus Traps incoming pathogens and prevents them from reaching cells they could infect Some mucous membrane tissue is lined with cilia – Hair-like extensions capable of wave-like movement – This movement moves trapped pathogens up and out of mucous-lined tissues like the trachea Cells that secrete mucus also secrete an enzyme called lysozyme which chemically damages pathogens

14 6.3.4 Phagocytic Leucocytes Leucocytes = white blood cells in the bloodstream which help us fight off pathogens that enter our bodies and provide immunity for many pathogens One type of leucocyte = macrophage- large WBCs that can change their cellular shape to surround an invader and take it in through the process of phagocytosis Moves similar to an amoeba (pseudopods), so it is referred to as amoeboid motion Macrophages can squeeze in and out of small blood vessels = can fight invaders outside of the bloodstream


16 Macrophages Can recognize a cell as a natural part of the body (“self”) or not a part of the body (“not-self”) – Based on proteins molecules that make up part of the surface of all cells, bacteria (cell membrane) and viruses (protein coat) If “not-self” the macrophage engulfs invader by phagocytosis Phagocytes contain many lysosome organelles to help chemically digest the pathogen Non-specific response = identity of pathogen not known, just that it is “not-self”

17 6.3.5 Antigens and Antibodies Antigens are molecules our bodies recognise as “not-self” ex. bacteria (cell membrane proteins) and viruses (protein coat) – foreign proteins are antigens Most pathogens have several different antigens on their surface Antibodies are protein molecules that we produce in response to a specific type of antigen Measles, flu, etc. Each type of antibody is different in response to a different pathogen


19 6.3.6 Antibody Production Similar to each other Each antibody is a protein that is Y shaped Binding site at the end of each fork of the Y Binding site is where antibody attaches itself to an antigen Y Y Y Y Y Y Antibodies specific for an antigen on surface of bacterium Cytoplasm containing ribosomes and plasmids mesosome

20 B Lymphocytes Leucocytes that produces antibodies We each have many types of B lymphocytes Each produces only a small number of antibodies relative to a massive infection that may occur; however, our immune response has a way of producing many antibodies Steps of a typical immune response: 1.Specific antigen identified (e.g. a particular cold virus) 2.Specific B lymphocyte identified to produce an antibody which will bind to the antigen (proteins on the cold virus protein coat)

21 3.The B lymphocytes clone themselves (divide repeatedly by mitosis) to rapidly the number of the same type of B lymphocyte 4.The newly formed “army” begins antibody production 5.Newly released antibodies circulate in the bloodstream and find their antigen match (the proteins of the pathogen) 6.Using various mechanisms, the antibody helps eliminate the pathogen 7.Some of the cloned antibody-producing lymphocytes remain in the bloodstream and give immunity from a second infection by the same pathogen. These are called memory cells.

22 6.3.7 Effects of HIV on Immune System HIV = human immunodeficiency virus – Results in a set of symptoms collectively called AIDS (acquired immune deficiency syndrome) – Viruses must find a type of cell in the body that matches their own proteins in a complementary way Only certain body cells are damaged by certain viruses Reflected in the symptoms associated with a particular infection Ex. a cold virus locates proteins on mucous membrane cells in your nasal region and damages those cells resulting in swelling of the area and excess mucus production- this virus does not affect other body cells that do not have the same protein

23 Only certain cells in the body have protein in their membrane that HIV recognizes One of these cells function as a communicator cell in the bloodstream – called a helper-T cell (this is the cell that HIV infects HIV has a latency period (infection occurs, but cells remain alive)….i t is usually many years after HIV infection that the symptoms called AIDS develop Helper- T cells are the cells that communicate which cells need to undergo cloning and begin antibody production When helper-T cells begin to die, communication no longer occurs and antibodies do not get produced Secondary infections (cancer, pneumonia, etc.) ultimately take the life of someone with AIDS.


25 Topic 6.3.8 Cause, Transmission & Social Implications of AIDS Causes already outlined in previous slides – HIV infection of the helper-T cells Difficult to find vaccine or cure because HIV “hides away” inside host cells for years Body’s immune responses continue to work against other pathogens, but not to combat the HIV because it is already inside body cells waiting for a chemical signal to become active The virus also mutates relatively quickly for a virus – Body’s immune responses or vaccines may not even recognize HIV after several mutations

26 Adding to the difficulty of developing medication is the association of HIV with sexual activity and drug abuse – This led to some reluctance to allocate $$$ for HIV research – Today huge sums of $$$ are allocated for HIV/AIDS research, but this is a relatively new development Transmission of HIV has another historical significance which has affected how society has responded to the disease – Transmitted from person to person by body fluids – Body fluid exchanges during sex and reusing unsterile syringe needles for legal or illegal drug injections AIDS was originally labeled as a disease affecting homosexuals and drug abusers

27 At one time, blood for transfusions wasn’t tested for blood-borne diseases like HIV People became HIV positive from transfusions Today, in countries with reasonable medical care, blood is routinely tested AIDS is rapidly spreading by way of heterosexual encounters and everyone is at risk HIV positive individuals may be discriminated against: – Employment – Insurance – Education access – Social acceptance


29 Not every country has the education and medical facilities to deal with this disease Until a cure is found, perhaps the best that can be accomplished is to: 1.Continue to lengthen the lifespan of those infected 2.Educate people on how to decrease their risk of exposure to HIV AIDS is truly a global problem – effective treatment and education must not be limited to certain countries

30 Diagnosis of HIV Enzyme-linked immunosorbent assays (ELISA) are used to detect the presence or absence of a particular protein For example, people recently infected with HIV will initially produce antibodies against HIV. These antibodies can be detected by ELISA to determine if a patient is HIV positive or negative





35 Assignment On the night of August 28 th 1987, a small home in the town of Arcadia, Florida was burned in a fire that was determined to have been started on purpose. Report on this event by reading the handouts – What, where, when, why, how and your reaction. You could also search the internet for more about the Ray family This is due Friday 5-14

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