Download Gastrointestinal System

Gastrointestinal System Histology
Dr. Twana A. Mustafa
GI: Overview: Organ systems
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Gastrointestinal (GI) tract [Alimentary canal] a
continuous muscular digestive tube
 Digests:
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Absorbs:
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breaks food into smaller fragments
digested material is moved through mucosa into the blood
Eliminates:
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unabsorbed & secreted wastes.
Organ systems
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Includes:
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Mouth, pharynx &
esophagus
Stomach
Small intestine
Large intestine
Accessory digestive
organs: teeth, tongue,
gall bladder, salivary
glands, liver &
pancreas
Figure 23.1
Processes
Ingestion
 Propulsion
 Mechanical digestion
 Chemical digestion
 Absorption
 Defecation
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Processes
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Ingestion: obtaining food
Propulsion: moves food along the GI tract by
peristalsis (wave-like muscular contraction)
Mechanical digestion :
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chewing & mixing with saliva
mixing in stomach
segmentation (local constriction in intestine to mix food
& digestive juices)
Processes

Chemical digestion: breaks down food to
molecular fragments (monomers) (Hydrolysis).
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
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Begins in the mouth with saliva & continues into the
small intestine.
Absorption: movement of nutrients across the
mucosal membrane into blood/lymph
Defecation: eliminates unused/indigestible &
secreted substances from the body
Functional Considerations :
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Substances in the GI tract lumen are outside of
the body.
Multiple sensors & receptors line the GI tract to
monitor contents & respond to conditions.
Controls: intrinsic (local control) & extrinsic
(CNS)
Peritoneum : serous membrane
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Visceral peritoneum: covers the external surfaces of
most digestive organs
Parietal Peritoneum: lines the body wall
Peritoneal Space: potential space containing fluid
that separates the visceral & parietal peritoneum
Figure 23.5a
Histology

GI tract wall has 4 layers:
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Mucosa
Submucosa
Muscularis Externa
Serosa or Adventitia
Histology of the Alimentary Canal
Figure 23.6
Histology

Mucosa: The epithelial membrane that lines the GI
tract from mouth g anus.
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Secretes mucous, digestive enzymes & hormones
Absorbs nutrients
Protects from disease & from the GI contents
Mucosa; 3 layers:
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Epidermis
Lamina propria (loose ct :
contain capillaries & some
elements of MALT)
Muscularis mucosa
Histology

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Submucosa: moderately dense CT with blood,
nerve, lymph vessels & lymphoid follicles; rich in
elastic fibers
Muscularis externa: smooth muscle

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Responsible for peristalsis &
segmentation
Circular layer
Longitudinal layer
Sphincters: in some areas
the circular layer thickens;
act as valves
Functional Anatomy: Mouth


Mouth: lips, palate, &
tongue
Mouth cavity = Buccal
cavity
Functional Anatomy: Mouth
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Lips: extend from inferior margin of the nose to
the superior margin of the chin. Red area = red
margin, is poorly keratinized & lacks sweat or
sebaceous glands.
Palate:
 Hard palate: rigid surface against which food is
forced in chewing
 Soft palate: muscular structure that rises &
blocks off the nasopharynx during swallowing
Functional Anatomy: Mouth

Tongue: muscular tentacle composed of
interlaced muscle fibers that grips & repositions
food, mixes food with saliva & compresses food
to form a food bolus, prior to swallowing.
Functional Anatomy: Mouth
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Filiform papillae: rough surface
Fungiform papillae: house taste buds
Circumvallate papillae: house taste buds,
Foliate papillae: posterolateral; taste buds
Functional Anatomy: Mouth

Salivary Glands: intrinsic & extrinsic
 Intrinsic glands: scattered throughout the buccal
cavity mucosa
 Extrinsic glands: supply most of the saliva; outside
buccal cavity & supply secretions via ducts:
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Parotid
Submandibular
Sublingual
Functional Anatomy: Mouth
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Composition of saliva:
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97-99.5% H2O
Electrolytes:
pH 6.75-7.0
Amylase: (digestive enzyme)
Proteins: mucin, lysozyme, & IgA
Protection from microbes by saliva:
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IgA: immunglobulins in secretions
Lysozyme: bacteriostatic (inhibits bacterial growth)
Cyanide
Defensins: local antibiotic activity & when activated
promote chemotaxis by WBCs
Normal flora: convert salivary components to nitrates
then to NO. NO is toxic & bacteriocidal
Figure 23.07
Figure 23.11
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Teeth:
Primary: 2I 1C 2M x 2 = 20
2I 1C 2M
Permanent: 2I 1C 2PM 3M x 2 = 32
2I 1C 2PM 3M
Structures

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Crown: exposed above gingiva (gum)
Root: anchored by periodontal ligament to
the bone by a fibrous joint (gomphosis)