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Transcript
11.4: Immunity Healing and Protection Against Disease Recall that platelets are cell fragments that are produced in the bone marrow which aid in clotting blood. clotting- solidification of blood where a blood vessel has been injured Remember fibrin gets produced to eventually form a scab. The blood’s ability to clot is reduced in 2 ways: by not having enough platelets or by having a vitamin K deficiency. Immunity Immune system- natural defences that the body has to fight against pathogens and maintain homeostasis; includes WBCs and proteins. Our immune system includes: - bone marrow - white blood cells (phagocytes and lymphocytes) - lymphatic system tissues (lymph nodes, tonsils, spleen and thymus) immunity which is the ability of our bodies to fight infection by producing antibodies or cells to inactivate the foreign particles. pathogens- viruses, bacteria and other microbes (fungus and protozoans) which cause disease; we are exposed to these every day in the food we eat, water we drink and air we breathe. Most microbes cause little or no damage to humans; many are involved in symbiotic relationships (i.e. E. Coli in wall of large intestine that helps human absorb nutrients. Defending against pathogens...2 groups of defense; 3 lines of defense: Non-specific defences- protect against variety of pathogens; protect the body from all pathogens in the same way; effectiveness doesn’t depend upon previous exposure. 1. First-Line Defenses- physical and chemical barriers like skin (unbroken), sweat, tears, saliva, cell membranes, mucus, stomach acid and urine 2. Second-Line Defenses- activated when pathogen gets by first-line defenses and starts infection Certain WBCs secrete a chemical called histamine which causes the area to become swollen, hot, painful and red (an inflammatory response). Histamine increases the flow of blood to the wound and allows more exchange in the capillaries so other white blood cells can attack the germs. Macrophages are giant white blood cells that destroy and engulf large amounts of bacteria by phagocytosis. This inflammation will cause fever to develop which will destroy some germs. Neutrophils & monocytes are other WBCs that attack bacteria using phagocytosis. Natural killer cells are WBCs which attack cancerous or viral-infected cells as well. Specific immune system- variety of cells that recognize foreign substances and act to neutralize or destroy them; develops over time in each individual depending upon which diseases a person is exposed to. 3. Third-line defense- activated when pathogen gets by first- and second-line defenses and into the bloodstream. The last line of defense is our immune system which recognizes, attacks, destroys and remembers each kind of pathogen by producing antibodies which bind to the pathogen and inactivate it. This line of defense is specific because our immune system produces antibodies which are specific to every different type of pathogen. When our bodies recognize foreign cells or particles, they produce antibodies or cells which bind to foreign substances and inactivate them. This is called an immune response. Antigens- foreign chemicals with large molecules on their surface (proteins or toxins) which enter a cell and cause an immune response White blood cells will attack antigens: lymphocytes- white blood cells designed to destroy specific antigens. There are 2 types: B cells and T cells and both are produced in the bone marrow and when they are mature they are released into the circulatory and lymphatic systems. B cells- remain in bone marrow T cells- mature in thymus gland There are 2 types of immune responses: Primary immune response- body’s initial response to an antigen; does not produce measurable amounts of antibodies during first 5 days after exposure, but amts. rise gradually over next 10-15 days (fig. 11.28 p. 384) Secondary immune response- rapid response by immune system when it is exposed to an antigen a second time; high levels of antibodies produced within 1-2 days Both of these responses involve 2 types of reactions: antigen enters body ↓ antigen gets ingested by macrophages; antigen’s form is shown on cell membrane of macrophage ↓ Cellular Immunity Antibody Immunity T-cell recognizes antigen B cell recognizes antigen helper T cell recognizes antigen shown on macrophage helper T stimulates T cell to forming killer T’s and memory T’s ↓ killer T’s bind to virusinfected cells ↓ suppressor T’s release substances to shut down killer T’s when foreign cells under control ↓ if antigen re-enters, memory T’s producing new killer T’s (secondary immune response) helper T stimulates B cell to forming plasma cells and memory B’s ↓ plasma cells produce antibodies that bind to antigen (antigenantibody complex) ↓ suppressor T’s release substances to shut down plasma cells when foreign cells under control ↓ if antigen re-enters, memory B’s producing new plasma cells (secondary immune response) There are 2 types of immunity: active immunity- body produces its own antibodies or killer T’s to fight antigen; may develop from having had a disease (i.e. chicken pox) or by vaccinations passive immunity- “borrowed”; person is given antibodies via blood from another person or animal; very fast, but temporary immunity because after about 1 mth., body destroys antibodies (i.e. baby in womb and breastfeeding) Disorders of the Immune System Allergy- rapid overreaction of immune system to an antigen which is not usually harmful. There are 2 types: - immediate (acute)- most common, occurs within seconds of exposure & usually disappears in 30 minutes - delayed Some common allergens (or allergy-causing antigens) include: hay fever (pollen), dust mites, insect stings, foods, pet dander. Symptoms may include: runny nose, swollen eyes, coughing, sneezing and rash. These symptoms result from the release of histamine at the reaction site. Histamines are chemicals which increase permeability of blood vessels; these cause an immune response (redness, swelling). The effects of histamine can be counteracted using drugs known as antihistamines. Autoimmune diseases- a person’s immune system fails to recognize body cells as “self” and produces antibodies against them. Examples include: juvenile diabetes, rheumatoid arthritis, multiple sclerosis and lupus. These autoimmune diseases can be inherited or can be caused by viral or bacterial infections. Cancer- disease in which cells multiply out of control. Cancer cells probably form in our bodies all the time, but in healthy people T cells destroy them.