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GUT PHYSIOLOGY
Motility
Dr. Jack Grider
Rm 12-004 Sanger Hall
828-1853
[email protected]
2009
Gut Smooth Muscle
A Unitary type smooth muscle
Gut Smooth Muscle
Two types of electrical activity
Slow Waves
Spike or Action Potentials
Gut Smooth Muscle
Slow Waves
Gut Smooth Muscle
Slow Waves
Gut Smooth Muscle
Slow Waves
Gut Smooth Muscle
Slow Waves
Force (g)
Potential
(mV)
+ ACh
Gut Smooth Muscle
Spikes/Action Potentials
(ACh)
contraction ~ # spikes
Gut Smooth Muscle:
Innervation
Longitudinal Layer
>few nerve fibers means
diffusion from MP
& gap junction impt
>ACh predominates
>minor relaxant
innervation
Circular Layer
>dense nerve fibers; release
from varicosities
>excitatory & inhibitory
>relaxant tone
predominates
Gut Smooth Muscle:
Innervation/ICC as Mediator
Gut Smooth Muscle
Reciprocal Innervation, Law of Intestine, Short Arc Reflexes
Gut Smooth Muscle
*
Motility/Swallowing
Oral & Pharyngeal Phase
• Initial events are
reflexive & mediated
by pontine &
medullary centers.
• Long arc reflexes
mediate initial
swallowing events.
Motility/Swallowing
Oral & pharyngeal phases
Motility:Swallowing
Esophageal phase:Primary Peristalsis
Vagovagal long arc reflex
Esophageal phase:
Primary vs Secondary Peristalsis
Motility: Swallowing
Vagal Efferent Innervation
Motility: Swallowing
Vagal Efferent Innervation
Motility
Swallowing
Motility
Gastric
STORAGE
EMPTYING
Motility: Gastric Electrical
Electrical activity determines types of
motilty patterns seen in stomach
Motility Gastric
• Three types of motility
– 1. Receptive relaxation
– 2. Adaptive relaxation (Accommodation)
– 3. Peristalsis
– Both determine duration a meal spends in
the stomach and rate of gastric emptying of
a meal.
Motility Gastric
• Receptive relaxation and Adaptive
relaxation (accommodation) comprise
initial motility response to a meal.
Motility Gastric
• Receptive relaxation and Adaptive relaxation
are mediated by vago-vagal long arc reflexes.
Adaptive relaxation additionally utilizes
enteric short arc reflexes.
Adaptive Relaxation
Receptive Relaxation
Afferent neurons
are solid; efferent
neurons are open
Enteric VIP/NO motor neurons
cause relaxation primarily of
gastric fundus
Distension
Stimulus
Motility
Gastric
Vagal transection prevents receptive and adaptive relaxation resulting
In a rise in intragastric pressure as the stomach fills during a meal.
Gastric Motility
After the intial phase dominated by relaxation, the
distension and digestive products in the chyme provide
the stimulus for gastric peristalsis which follows underlying
Myoelectrical activity.
3/min
Motility
Gastric Peristalsis & Emptying
Most chyme is propelled back into corpus/fundus
As peristaltic wave enters antropyloric region, powerful contractions
crush larger particles and propel them back into corpus/fundus.
Motility
Gastric Peristalsis & Emptying
Emptying depends on coordination of contractions
in antrum and pylorus by the peristaltic wave
Motility
Gastric Emptying
Emptying of a
non-nutrient meal
Nutrient content and
gastric secretions alter
these emptying curves.
• Gastric emptying for
liquids is more rapid
that for solids
• Rate of GE is
proportional (linear)
to  of volume
remaining in
stomach (gastric
distension)
– initial emptying is
more rapid
Motility
Gastric Emptying
• Contents of chyme slow gastric emptying by
activating intrinsic (short arc) and extrinsic (long
arc) neural pathways and by release of hormones
from intestine.
–
–
–
–
–
HCl: secretin
*Lipid digestion products: CCK**, GIP, PP/PYY
Protein digestion products: CCK, gastrin
Osmolarity
Duodenal distension
– *most potent
– **CCK activates vago-vagal reflex.
Motility
Gastric Emptying
Hormonal and neural agents slow GE by altering
antroduodenal and intestinal contractility