Objectives:<br />Describehow your body keeps out pathogens.<br />Explain how the immune system fights infections.<br />Describe four challenges to the immune system.<br />
First Lines of Defense<br />Your skin is made of many layers of flat cells. <br />Theoutermost layers are dead. As a result, many pathogens that land on your skin have difficulty finding a live cell to infect.<br />
Failure of First Lines<br />Sometimes, skin is cut or punctured and pathogens can enter the body. <br />Cell parts in the blood called platelets help seal the open wound so that no more pathogens can enter.<br />Immune system <br />The cells and tissues that recognize and attack foreign substances in the body.<br />
Cells of the Immune System<br />Macrophages<br />Engulf and digest many microorganisms or viruses that enter your body.<br />T cells<br />Coordinate the immune system and attack many infected cells.<br />B cells<br />Make antibodies. <br />Antibodies<br />Proteins that attach to specific antigens.<br />
Responding to a Virus<br />If virus particles enter your body, <br />Some of the particles may pass into body cells and begin to replicate.<br />Other virus particles will be engulfed and broken up by macrophages. <br />This is just the beginning of the immune response.<br />
Fevers<br />A moderate fever of one or two degrees actually helps you get well faster because it slows the growth of some pathogens.<br />Fevers also help B cells and T cells multiply faster.<br />
Memory Cells<br />Memory B cells<br />Cells in your immune system that “remember” how to make an antibody for a particular pathogen.<br />If the pathogen shows up again, <br />The memory B cells produce B cells that make enough antibodies in just 3 or 4 days to protect you.<br />
Challenges to the Immune System<br />Allergies <br />Happen when the immune system overreacts to antigens that are not dangerous to the body.<br />Autoimmune Disease <br />Disease in which the immune system attacks the body’s own cells. <br />Immune-system cells mistake body cells for pathogens.<br />Bee sting allergy<br />Rheumatoid Arthritis<br />
Cancer <br />Disease in which the cells begin dividing at an uncontrolled rate and become invasive.<br />AIDS<br />The human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS).<br />HIV infects the immune system itself, using helper T cells as factories to produce more viruses.<br />
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