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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
Secretory IgA
Fluids with antimicrobial
properties: saliva,
stomach fluid, bile
GALT tissues: tonsils,
adenoids, lymphoid
tissue in the esophagus,
Peyer’s patches,
Microbial antagonism
Large variety of normal
Oral cavity alone: more
than 550 known species
of microorganisms
Esophagus and stomach
much more sparsely
Large intestine: billions
of microorganisms
Tooth and Gum
◦ If left undisturbed, normal
biota biofilm eventually
contains anaerobic bacteria
that can damage the soft
tissues and bones
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
Initial stage: gingivitis
(swelling, loss of normal
contour, patches of
redness, and increased
bleeding of the gingival)
If persists, periodontitis
◦ Extension of gingivitis into the
periodontal membrane and
◦ 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
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
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 selflimiting 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
Uncommon in the U.S.
Frequent, watery
stools, fever, and
intense abdominal pain
Nausea and vomiting
are common
Often bloody stools