PY 105 Chapter Notes - Chapter 12: Myenteric Plexus, Submucous Plexus, Peristalsis
Digestive System
Overview
• Food contains molecules that are substrates in catabolic reactions and anabolic reactions
• Digestion is the breakdown of polymers into their building blocks
• Accomplished by enzymatic hydrolysis
• Food contains vitamins
• Digestion accomplished along the gastrointestinal (GI) tract - digestive tract, alimentary canal or
the gut
• The GI tract is a long, muscular tube extending from the mouth to the anus
• The inside of the gut is the GI lumen
GI Epithelium
• Lined with epithelial cells
• Epithelial cells are attached to a basement membrane
• The surface of the cells which faces the lumen is the apical surface
• There are folds called microvilli which increase surface area
• The apical surface is separated from the remainder of the cell surface by tight junctions, which are
bands running all the way around the side of epithelial cells, creating a barrier that separates body
fluids from the extracellular environment
• The sides and bottom of the cell are the basolateral surface
GI Smooth Muscle
• There are two layers of smooth muscle lining the gut: longitudinal layer running along the gut
lengthwise and circular layer which encircles it
• GI motility refers to the rhythmic contraction of GI sooth muscle
o Exhibits automaticity - contracts periodically without external stimulation
o Functional syncytium - when one cell has an action potential and contracts, the impulse
spreads to neighboring cells
o Enteric nervous system - GI tract contains own nervous system
o Hormonal input increases or decreases GI motility
o Sphincters relax which allow passage of food
• GI motility serves two purpose:
o Mixing of food and movement of food down the gut
• Mixing is accomplished by disordered contractions of GI smooth muscle
• Movement is accomplished by peristalsis
• A ball of food moving is called a bolus
Enteric Nervous System
• Branch of the autonomic nervous system
o Helps to control digestion
• Regulates local blood flow, gut movements and exchange of fluid from the gut to and from its
lumen
• Made up of two networks of neurons: the myenteric plexus and the submucosal plexus
o Myenteric plexus - found between the circular and longitudinal muscle layers and helps to
regulate gut motility
o Submucosal plexus - found in the submucosa and regulates enzyme secretion, gut blood
flow and ion/water balance in the lumen
GI Secretions
• Stimulated by food in the gut and by the parasympathetic nervous system and is inhibited by
sympathetic stimulation
• Two types of secretion: endocrine and exocrine
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