Presentation on theme: "Diseases of the gastrointestinal tract"— Presentation transcript:
1Diseases of the gastrointestinal tract Components of digestive tract (and sites of infection)Normal flora and other protective mechanismsPathogenesismany candidates: notice all of the tables in thischapter!
2Structure of the digestive system Ingestion (mouth)Digestion (mouth, stomach, small intestine)Accessory organs (liver, pancreas, gall bladder)Absorption (small, large intestineExcretion (large intestine)
3The oral cavity Many resident bacteria Some bacteria cause plaque (e.g., S. mutans, Actinomyces)Caries- breakdown of enamelPeriodonal diseaseCan cause systemic complecations
4Other infections of the mouth Mumpsspreads from upper respiratory tract to salivary glands; can spread to meninges; testesVaccine available since 1967 (MMR)Thrush (C. albicans)Herpes simplex type 1 (cold sores)
5Bacterial infections of the GI tract “Food poisoning”- toxins, other contaminantstoxins are already formed so onset is rapidTermed intoxication)S. aureus toxin is problematic because it is heat-stableSymptoms: diarrhea, pain, nausea, vomitingusually no immunity established“When in doubt, throw it out”
6Bacterial (gastro-)enteritis: organism causes disease, not exotoxinDiarrhea- small intestine affectedDysentery- large intestine (blood, pus)Enteric fever- systemicSalmonellamany distinguishable types (serovars)very common; usually spread by improperlyperpared foodsymptoms occur about 48 hours after infectioninvades mucosa in small, large intestines
7Shigella- not as invasive as Salmonella, but very contagiousbloody diarrheaS. dysenteriae produces a neurotoxinVibrio- cholera outbreaks occur when sanitation isdisruptedEnterotoxin makes interstines permeable to water;patients lose massive amountsfluid replacement, vaccinationMany other organisms produce enterotoxins (E. coli,Campylobacter, etc.
8Intestinal pathogens have different modes of activity Cholera toxinInvasiveness of Shigella
9H. pylori First cultured in 1982 (Marshall and Warren) Generates ammonia from ureaCauses peptic ulcersLinked to chronic gastritis, stomach cancer
10Most infectious enteritis probably caused by viruses Rotavirus (esp. young children)tends to be seasonalNorwalk virusvery common in adults2-day incubation periodPoliovirus: introduced by fecal-oral route but doesinfect digestive system
12Parasitic diseases of the digestive system Often transmitted from other animalsFood (beef, fish, pork, etc.)Incidental contact (soil, insects, feces)Helminths: Flukes, tapeworms (cestodes) roundworms (nematodes)Often symptoms are subtle or nonexistentCan infect diverse tissuesRequires antihelminthic drugs for treatment
13Infections by protozoans Giardia, etc.Cyst is hard to eliminateClean drinking water is importantHave complex life cyclesInvasion of tissues; inflammation
14Fungal toxins can be deadly Aflatoxins (moldy grain, peanuts)Strong carcinogensErgot (rye, wheat) can cause hallucinations; can be medicinalMushroom toxins mainly produced by Amanita; toxic to liver
15Summary Substantial opportunities for infection Bacterial/viral: no cure or lasting immunityDrugs for protozoan or helminthic infections pretty toxicVaccines limited (and often inappropriate)AvoidanceHydration therapy