Chapter 24 Notes.docx - Chapter 24 Notes Digestive System...

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Unformatted text preview: Chapter 24 Notes: Digestive System Infections Anatomy, Physiology, and Ecology of the Digestive System o The Upper Digestive System Includes mouth, salivary glands, esophagus, stomach The Mouth and Salivary Glands Teeth protected by enamel Proteinaceous material from saliva adheres, creates thin film (pellicle) Damage to enamel allows microorganisms to enter tooth, cause decay or dental caries Microbes can accumulate in gingival crevice o Gums become inflamed in response: gingivitis o Gums may recede from tooth root, allow bacteria access The Esophagus Mucus and saliva containing secretory IgA bathes lining o Microbial population relatively sparse (because of above) The Stomach Most bacterial cells cannot survive, so normal empty stomach has few (because it is highly acidic) o The Lower Digestive Tract Small and large intestines, pancreas, liver The Small Intestine o As stomach contents enter, pancreas and liver add alkaline digestive fluids that neutralize acid o Villi, microvilli increase surface area The Large Intestine o Main function is to absorb water, vitamins o Bacteria make up about one-third of fecal weight o Within the large intestine: Bacteria degrade wide variety of foods including substances (for example, fibers) indigestible by stomach, small intestines Bacteria important to human health Bacteria prevent pathogens from colonizing; stimulate mucosal immunity; opportunistic pathogens Bacterial Diseases of the Upper Digestive System o Dental Caries (Tooth Decay) Signs and Symptoms Usually advanced before symptoms develop Discoloration, roughness, defect; tooth may break Severe throbbing pain of toothache usually first sign Causative Agent Streptococcus mutans; in body they live only on teeth Convert sucrose into extracellular insoluble polysaccharides called glucans (aid in colonization of teeth) o Glucans essential for development of dental caries on smooth tooth surfaces Pathogenesis Streptococci adhere to pellicle on tooth, create plaque Split sucrose into glucose and fructose; polymerize glucose into glucans and ferment fructose to lactic acid o Lactic acid lowers pH; glucans create thicker biofilm (allows the bacteria to stick together) Epidemiology Worldwide distribution; sucrose consumption, access to preventative dental care, genetics important factor Treatment and Prevention Drilling out cavity and replacing with filling Restricting dietary sucrose Fluoridation Brushing, flossing o Periodontal Disease Gingivitis: swelling and redness of the gums Chronic periodontitis: destructive response that damages structures that support teeth Signs and Symptoms Gingivitis marked by gums that are tender, bleed easily Chronic periodontitis characterized by bad breath, red shiny gums that bleed easily, loosening of teeth Causative Agent Dental plaque at point where gum joins tooth Mostly Gram-negative anaerobes Pathogenesis (progression of the disease) 1. Plaque, tartar accumulates, extends into gingival crevice 2. Bacterial products incite inflammatory response 3. Microbes release tissue-degrading enzymes that widen and deepen gingival crevice; allows plaque to spread 4. Membrane attaching root to bone weakens, bone softens Epidemiology Almost 90% at 65; smokers, impaired immunity are factors Treatment and Prevention Cleaning, minor surgery to remove; flossing and brushing Viral Diseases of the Upper Digestive System o Mumps Signs and Symptoms Onset marked by fever, loss of appetite, headache Followed by painful swelling on one or both salivary (parotid) glands Spasm of underlying muscle makes talking, chewing hard Symptoms can arise elsewhere in body (sign of more serious infection) Headache, stiff neck indicative of meningitis Causative Agent Mumps virus: enveloped, single-stranded RNA virus Pathogenesis Virus inhaled via saliva droplets, spreads via bloodstream Virus multiplies in parotid salivary glands, inflammatory response to viruses in saliva yields severe swelling, pain Epidemiology Humans only natural host Was common in the U.S. prior to routine vaccination Treatment and Prevention No effective treatment, but attenuated vaccine available in U.S. since 1967 as part of measles, mumps, rubella, and varicella vaccine (MMRV) Bacterial Diseases of the Lower Digestive System o General Characteristics of “all” Lower Digestive infections Signs and Symptoms (lower digestive system infections) Diarrhea, loss of appetite, nausea and vomiting; fever Incubation period is a day or two but varies with dose Infection of small intestine: copious watery diarrhea Infection of large intestine: smaller amounts containing mucus, pus, sometimes blood o Dysentery refers to illnesses with blood, pus in feces Causative Agents Enterobacteriaceae: Shigella, Salmonella, E. coli Pathogenesis Different approaches; strains within species can differ, and individual strain may use multiple mechanisms Attachment often prerequisite Additional mechanisms are toxin Epidemiology Transmission via fecal-oral route commonly from food or water contaminated with animal or human feces Intestinal pathogens sensitive to acid usually have high infecting dose, since most are destroyed by acid Acid-resistant pathogens have low infecting dose Treatment and Prevention Oral rehydration therapy (ORT) used to counteract loss of fluid and electrolytes from diarrhea Sewage treatment, handwashing, chlorinating drinking water important control measures Bacterial Diseases of the Lower Digestive System o Cholera (Severe and potentially fatal diarrhea) Signs and Symptoms Classic example of severe watery diarrheal disease Vomiting may occur at onset; severe muscle cramps result from loss of fluids and electrolytes Severe dehydration can lead to organ failure and death Causative Agent Vibrio cholerae Pathogenesis Sensitive to acid, so large numbers must be ingested Adhere to epithelial cells of small intestine, establish infection, produce cholera toxin, an A-B toxin o B portion attaches to receptors of microvilli in intestine o A portion enters cells, activates a G protein Main idea here is A toxin leads to water loss Epidemiology Fecally contaminated water most common source Relatively common worldwide; relatively few cases in U.S. since early 1900s Treatment and Prevention Replacement of fluids and electrolytes o Escherichia coli Gastroenteritis Signs and Symptoms Depend on strain; some cause watery diarrhea, others dysentery Causative Agent Escherichia coli: Gram-negative rod Epidemiology Based on symptoms and pathogenesis of infecting strain Treatment and Prevention Most cases self-limiting, so antibiotics not routinely used o Salmonella Gastroenteritis Signs and Symptoms Diarrhea (sometimes bloody), abdominal cramps, nausea, vomiting, headache, fever Causative Agent Salmonella enterica: Gram-negative rod Pathogenesis Most sensitive to acid, so high infectious dose Attach to epithelial cells of distal small intestine Epidemiology Most cases from nonhuman animal sources Bacteria sometimes survive for months in soil and water Poultry, eggs often contaminated Treatment and Prevention Most recover without antibiotics Many strains antibiotic resistant Sanitary handling of food; cooking o Typhoid and Paratyphoid Fevers Signs and Symptoms Progressively increasing fever over a number of days, severe headache, constipation, abdominal pain In severe cases, intestinal rupture, bleeding, shock, death Causative Agents Salmonella serotypes Typhi and Paratyphi Pathogenesis Enteric fevers caused by bacteria that colonize intestines, cross mucous membrane, multiply within macrophages, and are disseminated via bloodstream Systemic infection causes fever, abscesses, sepsis, and shock, often with little or no diarrhea Epidemiology Humans only known host, so spread person to person often via contaminated food or water Some bacterial survivors remain colonized in gallbladder, may shed high numbers for years Treatment and Prevention Antibiotics; some strains resistant Surgical removal of gallbladder and months of antibiotic therapy often necessary to rid carriers Two vaccines Viral Diseases of the Lower Digestive Tract—Intestinal Tract o Norovirus Gastroenteritis Signs and Symptoms Abrupt onset of nausea, vomiting, watery diarrhea Vomiting most severe in older children and adults, resolves within first day or two Causative Agent Noroviruses Pathogenesis Infect epithelium of upper small intestine, causing cell death and decreased production of digestive enzymes Epidemiology Transmission via fecal-oral route Vomit contains infectious particles, transmission via aerosols and contaminated surfaces can occur Highly contagious, infectious dose of only ~10 virions Treatment and Prevention No proven anti-noroviral medications No vaccine Natural immunity is short-lived Thorough handwashing with soap and water is important Viral Diseases of the Lower Digestive System—Liver o At least 5 unrelated viruses can cause hepatitis Inflammation of liver Jaundice (yellowing of skin and whites of eyes) is most noticeable sign Three types (A, B, and C) account for most cases o Hepatitis A Signs and Symptoms Acute illness; no known chronic form or carrier state Older children and adults develop jaundice, fever, fatigue, clay-colored feces, and vomiting after ~1 month incubation Causative Agent Hepatitis A virus (HAV), a non-enveloped single-stranded RNA virus Pathogenesis Following ingestion, reaches liver via unknown route Replicates, is released into bile, eliminated in feces Epidemiology Spreads via fecal-oral route, principally by contaminated hands, food, or water Many outbreaks traced to restaurants where food-handlers failed to wash hands High risk groups include children in day care centers, residents in nursing homes, international travelers Treatment and Prevention No antiviral treatment available Effective inactivated HAV vaccine available since 1995 o Hepatitis B Signs and Symptoms Acute disease rarely fatal; virus usually cleared within weeks or months of initial infection Can become chronic; one in five develop cirrhosis (scarring of the liver), liver failure, liver cancer, or other chronic liver disease Similar to other forms, range from asymptomatic to severe Causative Agent Hepatitis B virus (HBV) Remarkably resistant; virions can be infectious after a week outside the body Pathogenesis Bloodstream carries to liver Liver damage likely from cell-mediated immune response Epidemiology Transmitted in body fluids (saliva, blood, blood products, semen) so activities that mix fluids are risk factors In chronic infection, virus replicates and circulates in blood for years, often asymptomatically, which increases spread Treatment and Prevention No curative antiviral treatment First vaccine approved in early 1980s, consisted of HBsAg from blood of chronic carriers o At least 5 unrelated viruses can cause hepatitis ...
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