1. Life Science 6.2 Your Body Defenses

2. Objectives: Describehow your body keeps out pathogens. Explain how the immune system fights infections. Describe four challenges to the immune system.

3. First Lines of Defense Your skin is made of many layers of flat cells. Theoutermost layers are dead. As a result, many pathogens that land on your skin have difficulty finding a live cell to infect.

4. Failure of First Lines Sometimes, skin is cut or punctured and pathogens can enter the body. Cell parts in the blood called platelets help seal the open wound so that no more pathogens can enter. Immune system The cells and tissues that recognize and attack foreign substances in the body.

5. Cells of the Immune System Macrophages Engulf and digest many microorganisms or viruses that enter your body. T cells Coordinate the immune system and attack many infected cells. B cells Make antibodies. Antibodies Proteins that attach to specific antigens.

6. Responding to a Virus If virus particles enter your body, Some of the particles may pass into body cells and begin to replicate. Other virus particles will be engulfed and broken up by macrophages. This is just the beginning of the immune response.

9. Fevers A moderate fever of one or two degrees actually helps you get well faster because it slows the growth of some pathogens. Fevers also help B cells and T cells multiply faster.

10. Memory Cells Memory B cells Cells in your immune system that “remember” how to make an antibody for a particular pathogen. If the pathogen shows up again, The memory B cells produce B cells that make enough antibodies in just 3 or 4 days to protect you.

11. Challenges to the Immune System Allergies Happen when the immune system overreacts to antigens that are not dangerous to the body. Autoimmune Disease Disease in which the immune system attacks the body’s own cells. Immune-system cells mistake body cells for pathogens. Bee sting allergy Rheumatoid Arthritis

12. Cancer Disease in which the cells begin dividing at an uncontrolled rate and become invasive. AIDS The human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS). HIV infects the immune system itself, using helper T cells as factories to produce more viruses.