• GI tract is composed of eight main sections and augmented by four accessory organs

• Eight sections: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus

• Accessory organs: salivary glands, liver, gallbladder, and pancreas

• Also known as the digestive tract or alimentary canal

• The GI tract is an internal tube (lumen) that passes through the body; only chemicals absorbed through the GI tract actually gain entrance to the internal portions of the body

• Mucus• Secretory IgA• Peristalsis• Fluids with antimicrobial

properties: saliva, stomach fluid, bile

• GALT tissues: tonsils, adenoids, lymphoid tissue in the esophagus, Peyer’s patches, appendix

• Microbial antagonism

Large variety of normal biota

Oral cavity alone: more than 550 known species of microorganisms

Esophagus and stomach much more sparsely populated

Large intestine: billions of microorganisms

Tooth and Gum Infections◦ If left undisturbed, normal

biota biofilm eventually contains anaerobic bacteria that can damage the soft tissues and bones (periodontium) surrounding the teeth

◦ Introduction of carbohydrates to the oral cavity can result in breakdown of dentition

Most common infectious disease of human beings

Symptoms: often not noticeable, but range from minor disruption in the enamel to complete destruction of the enamel and deeper layers

Deeper lesions can result in infection to soft tissue inside the tooth leading to a toothache

97% to 100% of the population has some manifestation of it by age 45

Most are due to bacterial colonization and varying degrees of inflammation

Initial stage: gingivitis (swelling, loss of normal contour, patches of redness, and increased bleeding of the gingival)

If persists, periodontitis develops◦ Extension of gingivitis into

the periodontal membrane and cementum

◦ Increases the size of pockets between the tooth and the gingival and can cause bone resorption enough to loosen and possible lose the tooth

Syntergistic infections infolving Treponema vincentii, Prevotella intermedia, and Fusobacterium species

Together they produce several invasive factors that cause rapid advancement into the periodontal tissues

Severe pain, bleeding, pseudomembrane formation, and necrosis

• Incubation period 2o to 3 weeks• Initial symptoms: fever, nasal

discharge, muscle pain, and malaise

• May be followed by inflammation of the salivary glands, producing gopherlike swelling of the cheekcs (parotitis)

• Multiplication in the salivary glands followed by invasion of other organs, especially testes, ovaries, thyroid gland, pancreas, meninges, heart, and kidneys

• Heliobacter pylori thrives in the acidic environment of the stomach and has been linked to a variety of gastrointestinal ailments

• Gastritis: sharp or burning pain emanating from the abdomen

• Gastric ulcers are actual lesions in the mucosa of the stomach

• Duodenal ulcer: lesion in the uppermost portion of the small intestine

• Severe ulcers can be accompanied by bloody stools, vomiting, or both

• Long-term infection with H. pylori might be a contributing factor to stomach cancer

In the U.S., up to a third of all cases transmitted by contaminated food

Most cases are self-limiting and do not require treatment

Some (E. coli O157:H7) can be devastating

• Salmonellosis: can be severe (elevated body temperature and septicemia) or mild (vomiting, diarrhea, and mucosal irritation); symptoms usually spontaneously subide after 2 to 5 days

• Typhoid fever: fever, diarrhea, and abdominal pain; the bacterium infiltrates the mesenteric lymph nodes and the phagocytes of the liver and spleen; progressive and invasive that leads eventually to septicemia

Figure 22.10

Causes the most severe form of dysentery

Uncommon in the U.S. Frequent, watery

stools, fever, and intense abdominal pain

Nausea and vomiting are common

Often bloody stools