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Transcript
Ch. 43 – the immune system Essential Knoweldge 2.D.4 (a-b) Overview A virus uses the machinery of your cells to make more copies of itself, until it destroys the cell; when that happens, the cell bursts and releases all the new viruses into your body to repeat the process Without the immune system, we’d be in big trouble. Overview There are 2 basic types of immunity; innate and acquired Innate immunity Is present before any exposure to pathogens and is effective from the time of birth (passed on from mother through the placenta or in breast milk) Involves nonspecific responses to pathogens (like a fever) Acquired immunity, also called adaptive immunity Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances Involves a very specific response to pathogens Figure 43.1 3 m How Immunity Works - Skin This is the first layer of defense Creates a barrier Has a low pH (which makes it hard for bacteria to live there) Chemicals on the surface of our skin disrupt certain viruses Bacteria (normal flora which just lives there) crowd out our skin which makes it hard for other substances to enter Certain cells of the mucous membranes produce mucus A viscous fluid that traps microbes and other particles Skin cont. If you get a cut, then there is a breach in your first defense Anitgens – any foreign invader in your body Internal cellular defenses Phagocytes, types of white blood cells Ingest invading microorganisms Initiate the inflammatory response Inflammation occurs (chemicals are released that causes our body to respond) Depend mainly on phagocytosis (cell eating) For example – acne (an infection in the pores of your skin)– bacteria are living and eating under our skin Macrophages (a specific type of phagocyte found throughout your body) enter and eat the invaders (called antigens); this causes swelling. Macrophages secrete lysosomes into the antigen to destroy it; problem – it will attack anything not us, including organ transplants Specific immune response Specific immune responses mean that we have generated antibodies for a specific virus, so we won’t get the same cold twice Antigens (what’s invading the cell) have specific proteins on their surfaces To fight them, we have structures called antibodies (proteins produced by our bodies) They have very specific shapes that will allow them to connect to the antigen; this helps the macrophages find them, and it also makes it harder for the antigens to do their job Specific Immune Responses Cont. – B lymphocytes B Lymphocytes are 1 type of white blood cells or phagocytes (attack viruses in our bodies) Made in bone marrow Create a humoral response (means, “in the fluid” or in the “humors” – like blood, lymph material, insterstitial fluid) Produce antibodies A naïve B cell senses the shape of the antigen, sends out a chemical message, and the B lymphocytes produce the antibodies specific for that antigen Memory B cells are then created to help give us immunity for the rest of our lives Specific Immune Response cont T Lymphocytes T Lymphocytes target and kill the cells that are already infected (responsible for what’s called a cell-mediated response) Created in the thymus (a gland on top of our heart; this is where they get the “T” from) Create Killer T Cells or Cytotoxic T Cells (a type of T lymphocytes) which target cells that are infected, docks next to them, and kills them Causes cell death Helper T Cells You have an antigen that is eaten by a macrophage, which chops up the antigen and produces pieces of it on it’s surface using a chemical called MHC2; you then get a Helper T cell (another type of T Lymphocyte) which docks on the macrophage and senses the shape of that antigen using another chemical called CD4; this initiates both the humoral and cellmediated responses A Helper T cell tells the shape of the antigen to the B cells so they can make more antibodies, tells it to the macrophages which will then eat the invaders, and they activate the killer T cells so they can kill the infected cells Helper T cells basically initiate the entire immune response Acquired immunodeficiencies range from temporary states to chronic diseases These are the cells that are being infected by HIV AIDS • People with AIDS are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse • You don’t die from aids, you die from a secondary infection Because AIDS arises from loss of helper T cells, it impairs both the humoral and cell-mediated immune responses The loss of helper T cells results from infection by the human immunodeficiency virus (HIV) Autoimmune Diseases In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body Rheumatoid arthritis is an autoimmune disease leading to damage and inflammation of joints Multiple Sclerosis Secondary Exposure If you are exposed to a virus that you have previously experienced, you would already have antibodies, memory B and Memory T cells that can be quickly produced and fight off the cold before you feel its effects. Plant and Animal defense mechanisms Plant can use nonspecific defense (have no immune system response) – it kills anything that invades or moves inside the organism Hypersensitive response (a plant can sense proteins given off by bacteria by using its “R” gene) – reminder from ch. 39, plant responses Let’s off an oxidative burst, that kills the cells, even if it’s not infected It also gives off a protein that changes the cell walls of all the adjacent cells Doesn’t have memory, so it will go through the same process if it’s infected again