ANHB2214 Study Guide - Final Guide: Enterocyte, Anal Canal, External Anal Sphincter
3 Jun 2018
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The Digestive System:
• Functions of the layers of the GI tract
o Surface epithelium
▪ Promote absorption of products of digestion
▪ Facilitate transport of food
▪ Produce mucus
o Lamina propria
▪ Protection → rich in lymphoid tissue
▪ Houses mucousal glands
▪ Capillaries nourish overlying epithelium/glands
o Muscularis mucosa
▪ Moves mucosa locally to improve contact with food
▪ Unique to GI tract
o Submucosa
▪ Pathway for arteries, veins and nerves
▪ Allows mucosa and muscularis externa to move
independently
o Muscularis externa
▪ 2 layers → inner circular and outer longitudinal
▪ Mixes and propels food in digestive tract
▪ Conraction coordinated by myenteric and submucosal
nerve plexuses
o Aventitia
▪ Covers segments of gut that attach to surrounding tissue
▪ Elsewhere → replaced with serosa
• Glands
o Formed by lining epithelium growing into underlying tissue
o Produce mucus → drains to surface through ducts
o Mucosal glands have 2 functions → secretion and cytogenesis
• Projections into lumen
o Surface epithelium bulges into lumen due to a thickening of lamina
propria, submucosa or muscularis externa
o Thickening of muscularis externa causes sphincters
• Enteric nervous system
o Myenteric plexus → network of ganglia located between layers of
muscularis externa
o Submucosal plexus → controls smooth muscle of mucosa
o GI tract initiates/controls its own activities intrinsically
• Esophagus
o Muscular tube
o Function → conducts food from mouth to stomach
o Lined with non-keratinized stratified squamous epithelium
o Glands in submucosa secrete mucus to lubricate tube
o Upper 1/3 → skeletal muscle
o Middle 1/3 → skeletal and smooth muscle
o Lower 1/3 → smooth muscle
o Cardiac sphincter controls passage of food into stomach
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