Digestive Tract

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Digestive Tract

• A journey through
• The Alimentary Canal

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Digestive Tract

• a) Oral Cavity
• b) Tubular Tract
• c) Major Digestive Glands

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Digestive Tract

• Functions
• a) physical treatment mastication
• b) secretion water, bicarbonate, enzymes
• c) chemical treatment - digestion
• d) transportation - swallowing, peristalsis.
• e) absorption assimilation
• f) elimination - defecation

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Oral Cavity

• Lips - skeletal muscle embedded between
• a) inner fibroelastic areolar (lamina propria)
  covered with non-cornified stratified squamous
  epithelial mucosa, continuous with cheek (same
  except addition of sub-mucosa in cheek).
• b) outer fibroconnective CT (dermis) covered
  with cornified strat. squamous epithelium
  (epidermis).
• No hair or glands, moistened only by licking

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Oral Cavity

• Tongue - skeletal muscle core covered with
  mucosa.
• Upper surface rough, non-cornified stratified
  squamous epithelium with papillae.
• Upper surface divided into two regions
• 1) lingual tongue - free, distal half covered
  with
• tall hair-like papillae in rows on anterior
  center of the tongue (filiform)
• mushroom shaped papillae on tip of tongue
  (fungiform)
• leaf-shaped papillae on side of tongue (foliate)
  - poorly developed in humans.

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Tongue

• 2) lymphoid tongue - basally attached zone
  separated from the lingual by a V-shaped groove
  (sulcus pit Sulcus terminalis).
• Large papillae line the back margin of the pit
  each papilla is surrounded by a moat (ditch) -
  Circumvallate papillae 7-12 in number.

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Taste Bud
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Salivary Glands

• Secrete saliva (water, salts, mucin, lysozyme,
  and amylase) into the oral cavity.
• Function in lubrication, starch digestion and
  anti-microbial action.
• Three glands
• Parotid
• Submandibular
• Sublingual

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Salivary Glands

• Parotid Gland - largest salivary gland
• Paired, anterior and below the ear
• DICT capsule with many septa.
• Parenchyma of simple cuboidal serous cells
• Myoepithelium around acini.
• Ducts - 3 levels
• 1) intercalated - small, most abundant simple
  cuboidal epithelium. Intralobular.
• 2) striated - larger, fewer simple columnar
  epithelium with basal striations. Intralobular.
• 3) excretory - largest empty into the oral
  cavity columnar -gt pseudostratified columnar -gt
  stratified columnar epithelium. Interlobular.

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Parotid Gland
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Salivary Glands

• Submandibular (Submaxillary) Gland -
• Paired below the ramus of the mandible
• Parenchyma mostly of serous with some mucous
  cuboidal epithelium
• Striated ducts more prominent.
• Sublingual Gland
• Group of small glands on the floor of the oral
  cavity beneath the tongue.
• Each glandular body has its own ductule system.
• Parenchyma mixed with mostly mucous cuboidal.
• Intercalated ducts reduced in length and number.

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Teeth

• 32 in adult derived from ectoderm and mesoderm.
• Two major parts
• a) Crown - exposed above gum (gingiva).
• Enamel outer surface dentin middle layer
  dental pulp cavity interior.
• b) Root - embedded in gum (gingiva). Cementum
  outer surface dentin middle layer dental pulp
  cavity interior.

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Teeth

• Tooth is firmly attached to jawbone by
  Periodontal Ligament of DICT
• a) Dentin - harder than compact bone
• - mostly inorganic salt (72), Collagen, GAGs
• - permeated by many canals Dentinal Tubules
• - tubules occupied by odontoblast processes
  (Tome's Fibers) of odontoblast cells.
• Odontoblasts from neural crest.

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Teeth

• Enamel hardest substance in the body.
• 96 inorganic salts secreted in alternating
  layers of enamel rods (prisms) of inorganic
  salts, and interrod matrix of inorganic salts and
  amelogenins.
• Enamel secreted by ameloblasts
• Ectodermal in origin.
• Enamel grows by layers Lines of Retzius.

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Dentin Tubules
Odontoblast Processes
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Teeth

• c) Cementum - covers dentin of the root similar
  to bone. Upper 1/3 is cell-less lower 2/3 may
  have osteons (w/o Haversian System and blood
  vessels) and cementoblasts-cementocytes in
  lacunae
• Formed by cells from the periodontal membrane.
• Periodontal Membrane - modified periosteum -
  occupies the space between the root and jawbone
  contains white fibers only. Fibers embed in
  cementum as Sharpy's Fibers.

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Teeth

• Dental Pulp - cellular matrix with fibers like
  mucoid CT
• Odontoblasts line the inner dentin surface. A
  single arteriole, venule and nerve are present.

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Pharynx

• Transition between oral cavity, tubular digestive
  tract, and respiratory tract.
• Stratified non-keratinized squamous epith.
• Ciliated pseudostratified columnar (with goblet
  cells) in area close to nasal cavity
• Contains tonsils
• Numerous small mucous salivary glands
• Constrictor and longitudinal (swallowing) muscles

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Tubular Digestive Tract

• Layers
• 1) Mucosa -
• a) epithelium
• b) lamina propria
• c) muscularis mucosa
• 2) Submucosa
• 3) Muscularis Externa -
• a) inner circular layer
• b) outer longitudinal layer
• 4) Serosa

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Four Layers

• Mucosa
• a) epithelium - mucous membrane irregular
  surface forms many glands, various tissue
  types.
• b) lamina propria - areolar CT thick layer,
  houses glands forms villi contains many
  lymphoid collections.
• c) muscularis mucosa - 2 thin smooth muscle
  layers inner circular and outer longitudinal.

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Four Layers

• Submucosa - areolar to fibroconnective CT deep
  and thick has many large blood vessels and
  autonomic ganglia Submucosal Plexus (Meissner).
• Muscularis Externa - thick smooth muscle layers
• Inner circular and outer longitudinal third
  diagonal layer added in the stomach.
• Terminal Ganglia present between the layers
  Myenteric Plexus (Auerbach).

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Four Layers

• Serosa - dense areolar CT
• if in body cavity and covered with simple
  squamous epithelium mesothelium (serous
  membrane).

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