Immune System: Nonspecific Defenses

1. Immune system protects body from "germs" and other harmful substances
2. First line of defense
• variety of barriers that keep most pathogens out of body
• pathogens: disease-causing agents, such as bacteria and viruses
• defenses in first line are the same regardless of type of pathogen
• mechanical barriers
• physically block pathogens from entering body
• skin is the most important defense against pathogens
• physical barrier between body and outside world
• skin is a tough, near-waterproof coating that is very difficult for pathogens to penetrate
• body openings (mouth, nose, etc) have different barrier
• mucous membranes line these openings
1. respiratory, gastrointestinal, and urinary tracts
• mucous membranes secrete mucus, a slimy substance that coats the membrane and traps pathogens
1. also have cilia, which sweep mucus and trapped pathogens toward body openings to be removed from the body
• pathogens removed from respiratory tract when you sneeze or cough
• tears wash away pathogens from eyes
• urine flushes pathogens out of urinary tract
• chemical barriers
• proteins that destroy pathogens at body's surface
• lysozymes kill pathogens by breaking open cell walls
• hydrochloric acid secreted by mucous membranes lining stomach kills pathogens that enter the stomach in food or water
• biological barrier
• living organisms that compete with pathogens
• bacteria cover skin, gastrointestinal, urinary, and genital tract areas
• bacteria are not harmful, and prevent harmful bacteria from becoming established in the body
• compete for food and space
• helpful bacteria may change pH to make conditions less suitable for harmful bacteria
3. Second line of defense
• inflammatory response
• red, warm, swollen, and painful injuries are signs of inflammatory response
• first responses of immune system to infection or injury
• triggered by cytokines and histamines
1. released when tissues are damaged
• cytokines: chemical signals used to communicate between cells
• histamines: chemicals that cause inflammation and allergies
• changes caused by cytokines and histamines help remove cause of damage and start the healing process
1. causes blood vessels to dilate, increasing blood flow to the area
4. White blood cells
• cytokines attracts white blood cells to the site of inflammation
• leukocytes are immune system cells that are specialized to fight infections
• primary cells of immune system and found all throughout the body
• leukocytes identify and remove pathogens, debris, and abnormal body cells
• some leukocytes are nonspecific
• monocytes, macrophages, neutrophils, eosinophis, and basophils
• part of second line of defense
• monocytes, macrophages, and neutrophils destroy pathogens in blood and tissues by phagocytosis
• process of engulfing and breaking down pathogens and unwanted substances
• pathogen broken down within macrophage