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Unformatted text preview: TOPIC 11. M ICROBIAL D ISEASES OF T HE RESPIR I TORY SYSTEM (ch24) 1. STRUCTURE AND FNCT ION OF T HE RESPIR I TORY SYSTEM (Figures 24.1 and 24.2 pg 677, 678) a) The respiratory system is comprised of the upper and lower systems. a. Upper respiratory system: i. Includes the nose, pharynx (throat) and associated structures (eustachian tubes, middle ear). ii. Has several defenses against pathogens including: 1. Nose hairs, 2. Cilia, 3. Mucus membranes 4. Lymphoid tissue (tonsils). iii. Infections of the upper respiratory system are the most common type of infection. b. Lower respiratory system i. Consists of the larynx (voice box), trachea (windpipe), bronchial tubes and alveoli (air sacs in lungs). ii. Also has several defenses against pathogens: 1. Pathogens in the lower system are generally removed by the ciliary escalator. 2. Pathogens reaching the alveoli are removed by alveolar macrophages. 3. Respiratory mucus contains secretory IgA antibodies. b) Pathogens that enter the respiratory system and are not removed can infect other parts of the body (systemic infections). 2. NORMAL M ICROBIOTA OF T HE RESPIR I TORY SYSTEM a) The normal flora of the upper respiratory system can include potentially pathogenic microbes. b) These potential pathogens usually do not cause disease because they are suppressed by the normal microbiota. c) The lower respiratory system is usually sterile because of the action of the ciliary escalator. 1 I. MICROBIAL DISEASES OF THE UPPER RESPIRITORY SYSTEM a) Specific areas of the upper respiratory system can become infected to produce: a. Pharyngitis (sore throat), b. Laryngitis (affects voice), c. Tonsillitis (inflammation of tonsils), d. Sinusitis (inflammation of sinuses) e. Epiglottitis (inflammation of epiglottis, potentially fatal). b) These infections are caused by different bacteria and viruses, including Streptococcus pneumoniae, S. pyogenes and Haemophilus influenzae. c) Most respiratory tract infections are self-limiting and non-fatal. 1. BACTER IAL D ISEASES OF T HE UPPER RESPIR I TORY SYSTEM A. STREPTOCOCCAL PHARYNGITIS (Strep Throat) (Figure 24.3 pg 678) a) Cause : a. This infection is caused by Streptococcus pyogenes , a group A -hemolytic streptococcus. i. The pathogenicity of this bacterium is increased by resistance to phagocytosis and production of: 1. Streptokinases: lyse fibrin clots. 2. Streptolysins: cytotoxic to tissues, RBC and leukocytes. b. Strep throat is most commonly transmitted by droplets. b) Symptoms : a. Include: i. Inflammation of the mucous membrane and fever; ii. Tonsillitis and swelling of the lymph nodes occurs; iii. Otitis media (middle ear infection; earache) may occur c) Diagnosis and treatment: a. Preliminary rapid diagnosis is made by indirect agglutination tests. Definitive diagnosis is based on a rise in lgM Ab....
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- Spring '08