04. Infectious Diseases: GASTROINTESTINAL SYSTEM

• Eight main segments of the gastrointestinal tract

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
  • Anus
• Esophagus


  • Not infected by microbes
  • Has peristaltic waves
• Stomach


  • For storage and digestion of food
  • Helicobacter pylori causes ulcers
• Small intestine


  • For nutrient absorption
  • Peyer's patches are packets of lymphoid tissue
• Large intestine


  • Mostly affected by infectious microbes
  • For water reabsorption
  • Contains probiotics (good bacteria for digestion)
  • Diarrhea is the main manifestation
• Rectum


  • Storage of fecal matter
• Anus


  • Should not be relaxed (contracted)
• Four accessory organs of the gastrointestinal tract

  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas
• Salivary glands


  Produce saliva, which is the first line of digestion of bigger carbohydrate molecules in the mouth
• Liver


  Produces bile, filters alcohol and other chemicals
• Gallbladder


  Storage of bile
• Pancreas


  Produces insulin to maintain carbohydrate balance, helps in hormone regulation
• The four accessory organs are considered to be free of natural microbiome
• Dysbiosis


  A condition wherein the normal barriers of the gut become disrupted due to unhealthy mixture of microbes
• Defenses against a heavy load of microorganisms in the gastrointestinal tract


  • Layer of mucus coating intestinal surfaces
  • Secretory IgA
  • Peristalsis keeps microbes moving
  • Saliva (lysozyme, lactoferrin)
  • Extremely low pH (acidic) in stomach
  • Bile is antimicrobial
  • GALT (gut-associated lymphoid tissue)
• Secretory IgA


  Immunoglobulin predominant in the GI tract
• Lysozyme


  Antimicrobial enzyme in saliva
• Lactoferrin


  Destroys cell membrane of microbes, "ferrin" means iron
• GALT(Gut-Associated Lymphoid Tissue)


  Protects body from invasion of pathogens, collection of lymphoid tissue in the GI tract
• Sphenopalatine ganglioneuralgia is brain freeze
• Vancomycin is one of the strongest antibacterial
• Noroviruses are a contagious virus that causes diarrhea and vomiting, with a high causation rate but low death rate
• Components of the oral microbiome


  • Bacterial species
  • Methane-producing archaea (methanogens)
  • Fungi (85 fungal genera, Candida albicans most common)
  • Few protozoa species
  • Virome
• Components of the gut microbiome


  • Esophagus and stomach (200 different species, most common firmicutes)
  • Large intestine (10^11 microbes per gram of contents, includes bacteria, fungi, and protozoa)
• Functions of normal gut biota

  • Protection
  • Teaches immune system how to react properly to microbial antigens (passive immunity, fever fights off foreign invaders)
  • Aid in digestion and provide nutrients (enterics, probiotics, prebiotics)
• Diverse gut microbiome is associated with health
• Oral Cavity Defenses

  • Saliva
  • sIgA
  • Lysozyme
  • Tonsils
  • Adenoids
• Oral Cavity Normal Biota

  
  

  • Prevotella
  • Treponema
  • Streptococcus
  • Actinomyces
  • Neisseria
  • Veillonella
  • Lactobacillus
• Rest of GI Tract Defenses

  • GALT
  • Lymphoid tissue
  • Peyer's patches
  • Appendix
  • sIgA
  • Rich normal biota
• Rest of GI tract Normal Biota

  
  

  ESOPHAGUS & STOMACH:

  • Streptococcus
  • Staphylococcus
  • Clostridium
  • Bacillus

  
  

  LARGE INTESTINE:

  • Bacteroides
  • Fusobacterium
  • Bifidobacterium
  • Clostridium
  • Streptococcus
  • Peptostreptococcus
  • Lactobacillus
  • Escherichia
  • Enterobacter
  • Candida and protozoa
• DENTAL CARRIES

  • Most common infectious disease of humans
  • Dissolution of the tooth surface due to the metabolic action of bacteria
  • Mainly caused by: Streptococcus mutans and S. sobrinus
• Scardovia wiggsiae – cause childhood carries
• Nursing bottle carries – rampant dental carries caused by putting a baby down to nap with a bottle
• Dental caries disease

  Causative Organism(s): A polymicrobial mixture of acid-producing bacteria
• Dental caries disease

  Most Common Modes of Transmission: Direct contact
• Dental caries disease

  • Virulence Factors: Adhesion, acid production
• Dental caries disease

  Prevention: Oral hygiene, fluoride supplementation
• Dental caries disease

  Treatment: Removal of diseased tooth material
• Dental caries disease

  Epidemiological Features: Calculus - deposits of food products / mineralized plaque
• Periodontitis

  • Initial stage: Gingivitis