Digestive Tract

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Digestive Tract

• Part II

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Esophagus

• Esophagus - about 10 in. long function
  transportation - swallowing.
• a) mucosa - epithelium - non-cornified
  stratified squamous epithelium.
• - lamina propria - glands present at lower end
  Cardiac Glands (shallow esophageals).
• - Muscularis mucosa present.

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Esophagus

• b) submucosa - coarse areolar forms thick folds
  giving esophagus a star shape. Deep esophageal
  glands present in lower ½. (ONE OF ONLY THREE
  PLACES IN THE BODY WHERE SUBMUCOSA HAS GLANDS)
• c) muscularis externa - mixed tissues upper 1/3
  is skeletal, middle 1/3 mixed smooth/ skeletal,
  lower 1/3 smooth muscle. Provides for the
  initiation of the swallowing wave.
• d) adventitia - areolar CT.

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Upper esophagus
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Stomach

• Not a simple sac-like structure as imagined -
• Sphincters (swollen muscle bodies) at both ends
  controlling back-flows.
• Food enters stomach as clumpy bolus and leaves as
  a white, semi-liquid chyme.
• Stomach wall is thrown into prominent
  longitudinal folds produced by the submucosa
  rugae, grinding devices, allows for expansion/
  stretching.
• Long gastric glands of the stomach are housed in
  the lamina propria.

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Stomach

• Stomach Regions
• a) Cardiac stomach
• b) Fundic stomach
• c) Pyloric stomach.
• Cardiac Stomach upper stomach, very small
  region Separated from esophagus by the Cardiac
  Sphincter.

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Cardiac Stomach

• Mucosa epithelium - simple columnar epithelium,
  cells are short-lived - 4-6 days, constantly
  replaced form gastric pits.
• Cardiac glands are mucous secreting some
  parietal cells are present.
• Lamina propria - house cardiac glands.
• Muscularis mucosa
• Submucosa - begin to form rugae.
• Muscularis Externa - a third inner, oblique layer
  appears contributes to cardiac sphincter
  formation.
• Serosa - no significance

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Fundic Stomach

• Major anatomical and functional stomach region.
• Mucosa - epithelium - as above gastric pits
  shallow fundic gastric glands long and straight
  produce most gastric juices
• Four cell types -
• a) Mucous Neck Cell - outer ½ of gland, mucous
  secreting, recruitment cell for gastric
  epithelium. Columnar epithelial cell.
• b) Enteroendocrine Cells - includes DNES cells
  and regular enteroendocrine cells (a.k.a.
  Argentaffin or Enterochromaffin cells) located
  in lower ½ of gland between chief cells secrete
  serotonin, histamine, gastrin, etc.
  Argyrophilic. Endocrine and paracrine cells.
• Originate from endoderm.

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microvilli
Enteroendocrine Cell
Secretory Granules
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Fundic Stomach

• c) Parietal Cell (oxyntic)- large, swollen acid
  staining cuboidal cell, contains carbonic
  anhydrase -converts CO2 HOH to bicarbonate
  (goes to blood) and protons (goes to gut as HCl),
  many mitochondria, eosinophilic
• Intrinsic Factor, glycoprotein (Vit. B12
  absorption factor) B12 deficiency causes
  pernicious anemia.
• d) Chief Cell - small, basophilic cuboidal cell
  most numerous cell type secretes pepsinogen and
  gastric lipase, probably rennin basally located.

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Mucosal Layer of Fundus Showing gastric glands
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Parietal Cell
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Pyloric Stomach

• Pyloric Stomach short, j-shaped region. Lesser
  digestive importance.
• Mucosa - epithelium - as in Fundus gastric pits
  wide and deep glands branched and coiled
  basally some parietal cells present columnar
  cells dominate.
• Muscularis Externa - 3 layers become 2 circular
  layer contributes to pyloric sphincter muscle.

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Pyloric Mucosa Deep pits, short glands
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Stomach

• Stomach Functions
• a) physical Rx. - extensive
• b) chemical Rx. - extensive
• c) absorption - water and alcohol
• d) transportation - Muscularis externa
• Gastric Secretion Control vagal stimulation,
  food presence, stomach wall stretching, and
  gastrin and histamine secretions.

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Small Intestine

• 20-23' long small diameter (1") with prominent
  structural modifications
• a) villi
• b) microvilli
• c) plicae circularis (mostly in jejunum)
• Duodenum - 10 - 12" long center of digestive
  activity.
• Mucosa - epithelium of 5 cell types
• a) goblet cells, columnar cells,
• b) absorptive tall columnar (enterocytes)
• c) Enteroendocrine cells (secretin, CCK, GIP,
  etc.)
• d) Paneth Cells, columnar cells
• e) Undifferentiated Cells

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Duodenum

• Glands
• a) endocrine cells (DNES) in mucosal
  epithelium
• b) intestinal glands (Crypt of Lieberkuhn)
• - in lamina propria columnar epithelial
  cells
• undifferentiated cells and Paneths (secrete
  lysozyme).
• c) Duodenal Glands or Glands of Brunner in
  submucosa, mucous secreting. Columnar cells.

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Paneths Cells Lysozyme stained
by Immunocytochemistry
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• - Lamina Propria - form villi tongue shaped in
  duodenum much lymphoid parenchyma.
• Submucosa - filled with Brunner's Glands forms
  Plicae Circulares.
• Muscularis Externa - traditional 2 layers.

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Duodenum

• Acid chyme stimulates release of GIP and secretin
  into blood vessels of upper duodenum
• GIP inhibits gastric secretion and muscle
  contractions.
• Secretin stimulates exocrine pancreas to release
  bicarbonate to neutralize acid chyme.
• Proteins and sugars of chyme stimulate release of
  CCK which stimulates exocrine pancreas to release
  trypsin, lipase amylase, etc.
• Fatty chyme stimulates release of cholecystokinin
  which stimulates gall bladder to release bile to
  emulsify fats for lipase digestion (smooth muscle
  contraction)

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Jejunum

• Jejunum 6 - 8' long accommodates much digestion
  and absorption.
• Mucosa - epithelium as in duodenum.
• - lamina propria - forms long, finger-shaped
  villi.
• Submucosa - no glands many plicae.
• Muscularis Externa - 2 layers of muscle.

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Ileum

• Ileum - 13 - 15' long completion of digestion
  and final absorption of nutrients.
• Mucosa - epithelium as above goblet cells
  increase in number.
• - lamina propria - forms club shaped villi
  Peyer's Patches present.
• Submucosa - plicae disappear.
• Muscularis Externa - 2 layers.

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Small Intestine

• Functions
• a) chemical Rx. - digestion completed.
• physical Rx. - none.
• absorption - most molecules.
• d) transportation - peristalsis, pendular,
  segmental gastroilic movement.

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Large Intestine

• Large Intestine - 5' long separated from small
  intestine by ilio-cecal valve
• Valve of mucosa and submucosa.
• a) cecum
• b) colon
• c) rectum
• d) anal canal

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Cecum

• Significance is in its position-shape and its
  giving rise to the appendix.
• Appendix - 3" finger-like diverticulum off the
  cecum epithelium with many DNES but few Paneth
  cells in fewer intestinal glands
• Lamina propria filled with lymphoid parenchyma
• Muscularis mucosa incomplete
• Submucosa and muscularis externa thin a
• Serosa present.

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Colon

• Colon 4-4.5' long lumen wide (2-2.5") and
  sacculated (haustra) forms ascending,
  transverse, and descending segments.
• Mucosa - simple columnar epithelium with many
  goblet cells intestinal glands longer than in
  small intestine no digestive function, absorb
  water.
• - lamina propria - lack villi.
• Muscularis Externa - outer longitudinal layer
  becomes thin and forms three, thick, longitudinal
  bands (Taenia coli) for compacting and moving
  feces.

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Rectum

• Rectum - lower end of colon lumen narrows.
• Similar organization as colon except muscularis
  externa becomes normal and intestinal glands
  disappear.
• - at upper end, when Taenia coli disappear,
  circular layer of externa is longer than
  longitudinal, when match up causes folding in
  submucosa-mucosa Plica Transversae,

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Anal Canal

• Anal Canal- lower one inch of the rectum.
• Mucosa - upper end of simple columnar epithelium,
  lower end non-cornified to cornified stratified
  squamous epithelium.
• - lamina propria - forms longitudinal folds
  Columns of Morgagni - poorly developed in
  adults.
• - muscularis mucosa - disappears in lower end.
• Submucosa - many large, thin-walled veins (future
  hemorrhoids?) and circumanal glands.
• Muscularis Externa - lower end of circular layer
  forms internal anal sphincter muscle layer
  disappears.
• Adventitia - gut tube becomes attached to
  adjacent dermis external anal sphincter of
  skeletal muscle forms just above anus.