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U N I T 8
Gastrointestinal and Hepatobiliary Function
U N D E R S T A N D I N G
Intestinal Motility
Motility of the small intestine is organized to optimize the digestion and absorption
of nutrients and the propulsion of undigested material toward the colon. Peristaltic
movements mix the ingested foodstuffs with digestive enzymes and secretions and
circulate the intestinal contents to facilitate contact with the intestinal mucosa.The
regulation of motility results from an interplay of input from the (1) enteric and (2)
autonomic nervous (ANS) systems and the intrinsic pacemaker activity of the (3)
intestinal smooth muscle cells.
Enteric Nervous System
Innervation.
The gastrointestinal
system has its own nervous system,
called the
enteric nervous system
.
The enteric nervous system is
composed mainly of two plexuses:
(1) the outer
myenteric (Auerbach)
plexus
that is located between the
longitudinal and circular layers
of smooth muscle cells and (2)
an inner
submucosal (Meissner)
plexus
that lies between the mucosal
and circular muscle layers. The
myenteric plexus controls mainly
intestinal movements along the
length of the gut, whereas the
submucosal plexus is concerned
mainly with controlling the function
within each segment of the intestine.
Fibers in the submucosal plexus
also use signals originating from
the intestinal epithelium to control
intestinal secretion and local blood
flow.
1
Mesentery
Myenteric
plexus
Serosa
Muscular
coat
Longitudinal
Circular
Submucosa
Submucosal
plexus
Villi
