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Defense Against Infectious Disease
Transcript of Defense Against Infectious Disease
Skin, Mucous Membranes, and other Physical Barriers IB Biology Section 6.3 Physical Barrier: Skin Physical Barrier:
Mucous Membranes The respiratory tract is another potential entry route, but it is protected by sticky mucous, which traps pathogens and other particles. The Second Line of Defense The second line of defence is the non-specific immune system, a host of quick, non-specific methods of killing microbes that have passed the first line of defence and entered the body. Pathogen:
An organism or virus that causes
a disease. Bacteria e.g. E. Coli Protozoa e.g. Malaria Parasite Viruses e.g. Influenza Virus Fungi e.g Epidermophyton Methods of Transmission of Pathogens: Inhaled Droplets Direct Contact Bodily Fluids Animal Vectors Blood Contact Ingested, Swallowed So the question is... How does the human body defend against pathogens? The skin is a tough, impenetrable battier comprised of several layers of cells. The outer layer (epidermis) has cells strengthened by the proteins keratin.
Cells are constantly being lost from the surface of the skin and being replace by new cells.
The enzyme lysozyme is present on the skin's surface to break down pathogens.
The slightly low pH of the skin makes it unfavorable to pathogenic agents. Mucous contains lyzozymes that compete with the pathogens. Mucous tends to be slightly acidic. Cilia constantly sweep the mucous upwards to the throat, where it is swallowed so that microbes are killed by the stomach. Skin and Membranes Overview But... What happens if the first line of defense fails? The key player in this second line of defense are phagocytic leukocytes. Phagocytic Leukocytes "Eating Cells, White Blood Cells" Phagocytes are large, irregularly-shaped leukocytes (white blood cells) that destroy bacteria, viruses, and dust particles by endocytosis. The phagocytes show amoeboid movement, constantly changing shape, as they engulf microbes. The microbes are engulfed in vesicles called phagozomes. The phagosome then fuses with lysosomes which contain lysozymes. These enzymes kill and digest the microbes. The process is called phagocytosis Antigens and Antibodies Now... There is also the third line of defense, which involves
specific responses to foreign invaders. To understand this response, we must know the
following terms: Antigen and Antibody Antigen: a substance or molecule, often present on a cell or virus surface, that causes antibody formation.
Antibody: a globular protein that recognizes a specific protein and binds to it as part of the immune response. Note a specific antibody binding to a specific antigen on the surface of the bacterial cell. Explain the Process of Phagocytosis: The production of antibodies by the immune system is one of the most remarkable processes... When a pathogen invades the body the immune system
produces large amounts of specific antibodies needed to combat the infection. Let's take a look. The Humoral (Specific) Immune Response Stages in Antibody Production Step 1: Antigen Presentation Macrophages (a type of white blood cell) take in antigens by endocytosis, process them, and attach them to membrane proteins on their surface called MHC proteins. Step 2: Activation of helper T-cells Helper T-cells have receptors in their plasma membrane that can bind to antigens presented by macrophages.
The inactive helper T-cell binds to macrophage presenting the antigen.
The macrophage sends a signal to activate the helper T-cell. Step 3: Activation of B-cells Activated T-cell can now stimulate the appropriate B-cell.
Inactive B-cells have antibodies in their plasma membrane. If these antibodies match an antigen, the antigen binds to the antibody.
An activated helper T-cell with receptors for the same antigen can then bind to the B-cell, and send a signal to activate the B-cell. Step 4: Production of Plasma cells Activated B-cells start to divide by mitosis to form a clone of cells known as plasma cells. They have an extensive network of rough endoplasmic reticulum to make large amounts of antibodies, which are secreted by exocytosis.
This is known as clonal selection. Step 4: Production of Memory Cells Memory cells are B-cells and T-cells that are formed at the same time as activated helper T-cells and B-cells, when a disease challenges the immune system.
After the activated cells and the antibodies produced to fight the disease have disappeared, the memory cells persist and allow a rapid response if the disease is encountered again.
Memory cells give long term immunity to a disease. What are the risks and benefits of vaccination? Blood Clotting http://www.footprints-science.co.uk/Bloodclotting.htm Why Are antibiotics ineffective against viruses?