PHS 3342 Lecture Notes - Lecture 16: Lamina Propria, Gastrointestinal Tract, Muscular Layer
28 Apr 2018
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March 27, 2018
Gastrointestinal System
GI System
Purpose of GI system is to provide a steady supply of nutrients, water, and inorganic ions to the body from food that
is eaten
Involves 4 key types of processes:
-Motility
-Secretion
-Digestion
-Absorption
GI Tract Anatomy
Digestive tract itself + accessory structures connected by ducts
Both ends of tract open to outside (through mouth and anus) - lumen of tract is continuous with external environment
Tract itself: mouth, pharynx, esophagus, stomach, small and large intestines
Accessory structure: salivary glands, pancreas, liver, gallbladder
Structure of the Wall of the GI Tract
Mucosa: 3 layers
-Mucous membrane (innermost layer): includes epithelial cells lining
that area of the GI tract
ā¢Beginning parts: stratiļ¬ed squamous epithelium
-Food is still rough at the beginning - need a sturdy, easily
replaceable lining
ā¢Deeper parts: single layer of columnar epithelial cells
-Donāt need the sturdy layer any more, need functional cells that
can secrete products or absorb nutrients
-Lamina propria: connective tissue layer for support
-Muscularis mucosa: thin muscular layer that inļ¬uence whether or not the mucosa are folded
-Not actually involved in the motility of the GI tract
Muscularis externa (outermost layer): smooth muscle layer involved in motility
-Inner circular muscle: wrapping around the tube
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March 27, 2018
-Outer longitudinal muscle: runs along the length of the tube
Serosa: ļ¬brous wrapping along the outer side of the GI tract that form sheets of tissue (mesentery) to provide
pathways for blood vessels
Innervated by the autonomic system:
-Myenteric plexus: involved in controlling muscularis externa - controls motility
-Submucosal plexus: involved in controlling the mucosa - secretion, folding, etc.
Layers of the GI Tract Wall
Mucosa: one of the main functional layers
-Functions:
ā¢Mucus, enzymes, and hormones
-Mucus is required to help with being able to propel food along the length of the GI tract, also protects the
lining of the GI tract by reducing frictional damage and protects against stomach acid
-Enzymes: mainly produced by the stomach and intestines
-Hormones: produced by endocrine cells in the wall of the GI tract that go into the bloodstream or into the
interstitial space to regulate GI actions
ā¢Absorption of digestion products
-Minimal absorption until the small intestine - some absorption of fat soluble products in stomach, majority of
absorption in small intestine, small amounts in large intestine
ā¢Protection against infection
-Food we eat isnāt sterile - helps protects against microorganisms
-Epithelial layers: columnar epithelial + goblet cells
ā¢Columnar epithelial cells everywhere except esophagus and beginning of tract
ā¢Goblet cells: produce mucus - interspersed in between epithelial cells along the length of the GI tract
-Lamina propria: CT + GALT (gut-associated lymphoid tissue) + capillaries
ā¢GALT = immune function
-Muscularis mucosa: thin layer of smooth muscle (movement of just mucosa)
Submuocsa: layer of CT with blood and lymph vessels that branch to inner mucosa and outer muscularis externa
-Exocrine glands + submucosal plexus (regulates glands and smooth muscle of mucosa/submucosa - secretion and
shape of inner lining of GI tract)
Muscularis externa: other main functional layer
-Inner circular muscle layer + outer longitudinal layer
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