抗生素英文课件精品Immune.ppt

Immune System Guarding against disease The not-so-common cold A “cold” is an infection of the mucus membranes of the respiratory tract by a rhinovirus. Over 100 rhinoviruses have been identified, which is one reason why we don’t become immune to “the cold.” Cold myths Colds and “the flu” are different illnesses. Not every respiratory infection is “the flu.” Colds are not caused by getting chilled. This belief comes from medical ideas of prior centuries, when it was believed that illness was caused by an imbalance of “humors,” and that a person with a cold actually had too much “coldness.” “Feed a cold, starve a fever” also comes from prior centuries, when it was thought that people with a cold had too much “cold” and “moisture” in their bodies, and needed food to increase heat, while people with fever had too much “dryness” and “heat,” so needed less food to cool them down. Cold vs. “Flu” (influenza) Virus vs. Bacteria Colds are caused by a virus, which is a non-living particle that contains genetic material, and hijacks your cells to reproduce. Bacteria are living organisms that can reproduce on their own. First line of defense Non-specific defenses are designed to prevent infections by viruses and bacteria. These include: Intact skin Mucus and Cilia Phagocytes Role of skin Dead skin cells are constantly sloughed off, making it hard for invaders to colonize. Sweat and oils contain anti-microbial chemicals, including some antibiotics. Role of mucus and cilia Mucus contains lysozymes, enzymes that destroy bacterial cell walls. The normal flow of mucus washes bacteria and viruses off of mucus membranes. Cilia in the respiratory tract move mucus out of the lungs to keep bacteria and viruses out. Role of phagocytes Phagocytes are several types of white blood cells (including macrophages and neutrophils) that seek and destroy invaders. Some also destroy damaged body cells. Phagocytes are attracted by an inflammatory response of damaged cells. Role of inflammation Inflamm