1. IV MOTILITY OF THE SMALL INTESTINE

2. Function of Intestinal Motility
To mix chyme with digestive secretion
To bring fresh chyme into contact with the absorptive surface of the microvili
To propel chyme toward the colon

3. Types of small intestinal movement
Tonic contraction: the base of the other contractions
2. Segmentation contractions
(1) def.
When a portion of the small intestine becomes distended with chyme,
the stretch of the intestinal wall elicits a rhythmical contraction and relaxation of localized circular muscles
spaced at intervals along the intestine,
(2) function:
mix the chyme with the digestive juice
increase its exposure to the mucosal surface
Prolong spread out
INTESTINAL MOTILITY & SPHINCTER CONTROL
SMALL INTESTINE
circular and longitudinal muscle layers function to:
mix contents with secretions
expose all contents to mucosal surface
mucosal cell enzymes
absorptive surface
propel contents through intestine
contractile events
slow waves initiated in orad duodenum
independent of slow waves in stomach
independent of contractile events in pylorus
have basal rate of 12/min (or 1 every 5 seconds)
this rate constant for duodenum and first part of jejeunum
rate decreases to 8/min in distal ileum
contractions will occur if spike potentials occur on top of slow wave
maximum rate of contraction in duodenum would be 12/min
contractions occur at intervals which are multiples of 5 seconds
spike potentials usually occur in short restricted segments
each contraction covers region of 1-4 cm
resulting contractions produce segmentation of the bowel
effect of each contraction depends on status of adjacent segments
mixing will occur with no other concurrent events locally
propulsion occurs if coordinated with adjacent segments
reflex responses to distension (bolus of material in lumen)
local response - myogenic involving enteric plexus
(law of the intestine, peristaltic reflex)
contraction proximal to region of stretch, relaxation distally
intestino-intestino reflex - involves extrinsic neurons
response to gross distension
with extreme stretch or injury, contractions cease (ileus)
response to central input - psychic factors
inhibition of contraction in other areas of intestine
MMC
originates in stomach
occurs only in fasting state (postabsorptive)
stimulated by motilin

4. Types of small intestinal movement
3. Peristalsis: propels the small intestinal contents towards the large intestines
peristaltic rush：initiated by the harmful stimulation
4. MMC:
Occurs during fasting state
moves any undigested material still remaining in the small intestine into the large intestine
prevents bacteria from remaining in the small intestine long enough to grow and multiply excessively
Prolong spread out
INTESTINAL MOTILITY & SPHINCTER CONTROL
SMALL INTESTINE
circular and longitudinal muscle layers function to:
mix contents with secretions
expose all contents to mucosal surface
mucosal cell enzymes
absorptive surface
propel contents through intestine
contractile events
slow waves initiated in orad duodenum
independent of slow waves in stomach
independent of contractile events in pylorus
have basal rate of 12/min (or 1 every 5 seconds)
this rate constant for duodenum and first part of jejeunum
rate decreases to 8/min in distal ileum
contractions will occur if spike potentials occur on top of slow wave
maximum rate of contraction in duodenum would be 12/min
contractions occur at intervals which are multiples of 5 seconds
spike potentials usually occur in short restricted segments
each contraction covers region of 1-4 cm
resulting contractions produce segmentation of the bowel
effect of each contraction depends on status of adjacent segments
mixing will occur with no other concurrent events locally
propulsion occurs if coordinated with adjacent segments
reflex responses to distension (bolus of material in lumen)
local response - myogenic involving enteric plexus
(law of the intestine, peristaltic reflex)
contraction proximal to region of stretch, relaxation distally
intestino-intestino reflex - involves extrinsic neurons
response to gross distension
with extreme stretch or injury, contractions cease (ileus)
response to central input - psychic factors
inhibition of contraction in other areas of intestine
MMC
originates in stomach
occurs only in fasting state (postabsorptive)
stimulated by motilin

5. Segmentation: mix contents to promote digestion & absorption

6. Peristalsis
Distinctive pattern of smooth muscle contractions that propels foodstuffs distally through the esophagus and intestines
Mediated by….
Local, intrinsic nervous system
Ex: peristalsis is not affect to any significant degree by vagotomy or sympathectomy

7. Small Intestinal Motility
Peristalsis: movement along the tract

8. Peristalsis
Figure 24.4

9. peristalsis

10. Peristalsis of the small intestine

11. Peristalsis – law of intestine
Berne et al., 2004

12. Peristalsis – law of intestine
Berne et al., 2004

13. Peristalsis – law of intestine
Berne et al., 2004

14. Peristalsis – law of intestine
Berne et al., 2004

15. Peristalsis – law of intestine
Berne et al., 2004

16. Peristalsis – law of intestine
Bolus of food →Mechanical distension and mucosal irritation → stimulates afferent enteric neurons → 2 effects
Excitatory motor neurons above the bolus activated → contraction of smooth muscle above the bolus
Via Ach, substance P
2. Inhibitory motor neurons → stimulate relaxation of smooth muscle below the bolus
Via nitric oxide, vasoactive intestinal peptide and ATP

17. Control of Intestinal Motility – Neuronal
Mixing – segmentation
Frequency set by slow waves (12/minute duodunum)
additional control: myenteric plexus
Propulsion – peristalsis
Local reflex – stretch causes relaxation distal and contraction proximal (Bayliss – Starling law of the intestines)
Moves bolus through intestines
Intestino-intestinal reflex – extrinsic nerves
Local stretch in one area inhibits contraction in rest of bowel
motility controlled by neural input
intrinsic (myenteric or Auerbach's plexus)
tonic inhibition of circular
tonic inhibition inhibited by opioids (increased segmental contraction)
Extrinsic
extrinsic
sympathetic: inhibitory
parasympathetic (vagal)
vagal input increases force of contraction because:
vagal input inhibits tonic inhibition (disinhibition)
vagal effects inhibited by nitric oxide (relaxation

18. Movement in Small Intestine
Peristalsis (ou propulsivos) e Segmentation (mixing)

19. Central and peripheral control of contractile patterns
Intestinal
wall
Vagal
centre
lumenl
Peptide (CCK)
Receptors
Glucose - Osmolality
Long chain fatty acids
Amino acids
Sensory neurons
Vago-vagal reflexes
Interneurons
Integrating circuits
Program circuits
Enteric nervous system
Motorneurons
Contractile
patterns
Luminal stimuli elicit vago-vagal reflexes which activate integrating and
program circuits of the enteric nervous system.
These activate specific motorneurones responsible for specific contractile patterns.

20. Control of Intestinal Motility – Hormonal
Gastrin Secretin
CCK motility Glucagon
5-HT VIP
Motilin GIP
hormonal & paracrine influences
inhibitory to contraction
catecholamines
secretin
glucagon
nitric oxide
VIP
excitatory to contraction
serotonin
gastrin
cholecystokinin
insulin
(motilin)
opioids

21. Ileocecal Valve What it is Opening to large intestines
Function: (1) prevent the repulsion (2) control the emptying
normally closed. Short-range peristalsis in terminal ileum and distension relaxes IC sphincter --> small amount of chyme is squirted into the cecum.
Distension of cecum contracts IC sphincter.
Gastro-ileal reflex: enhances ileal emptying after eating.
The hormone gastrin relaxes ileocecal sphincter.
Wall of ileum immediately preceding valve has thickened muscular coat called ileocecal sphincter
Normally constricted and slows emptying of ileal contents into cecum except immediately after a meal, when gastroileal reflex intensifies peristalsis in ileum
Functions to prevent backflow of fecal contents from colon to SI
are forcefully closed when any excess pressure builds up in cecum, usually cm H2O.
Resistance to emptying at ileocecal valve prolongs stay of chyme in ileum and therefore facilitates absorption.
When cecum distended, contraction of sphincter intensified, ileal peristalsis inhibited. When there is irritant in cecum, emptying delayed. As in acute appendicitis, which causes intense spasm of sphincter, ileal paralysis and blocks emptying of ileum.

22. V. GASTROINTESTINAL MOTILITY DURING FASTING STATE

23. Gastric motility on fasting
“Migrating Motor Complex, MMC”
Occurs during fasting
To clear undigested food particles
Peristaltic contractions sweep down stomach and duodenum – pylorus relaxes
Pattern of contraction approx every 90 min
Slow peristaltic waves sweeping whole of GI tract
Thought to be controlled by motilin (胃动素）
SWEEP approx

25. MMC(migrating motor complex)
contents
PhaseⅠ: Almost have no contractions min
PhaseⅡ: have contractions, only have few min
PhaseⅢ: have continuous contractions 5-10 min

26. The interdigestive motility consists of three phases
Interdigestive Cycles
Phases
Sporadic
peristaltic waves
Segmenting
contractions
and single
Motor
quiescence
of stomach
and duodenum
Contraction
of reservoir
Pylorus
Aboral migration
Accumulation of residues
of chyme
Phase II
Phase I
Stomach
Duodenum
Jejunum
Ileum
Phase III
III I II
Forceful
The phase III of the migrating motor complex (of dog)
Originates simultaneously at the stomach and duodenum
Migrates within 90 to 120 minutes along the small intestine

27. Importance of MMC
Sweep the contents of the small intestine towards the colon
Housekeeper of the small intestine
Inhibit the migration of colonic bacteria into the terminal ileum

28. VI MOTILITY OF THE COLON

29. Large intestine Functions Motility patterns
Absorption of water and electrolytes
Storage of feces
In non-ruminant herbivores, fermentative digestion and absorption of nutrients
Motility patterns
mixing (form haustrations)
propulsive (mass movements)

30. Segmentation in large intestine
Haustration: （结肠袋）modified form of segmentation in which intense, local contraction of circular muscle causes large intestine to appear to bulge into sacs

31. Mass movement Occurs in colon; also known to occur in equine cecum
Period of intense propulsive activity that moves entire contents of colon distally toward rectum
Contractions progress for long distance such that long length of colon contracts as a unit
Entry of fecal matter into recturn triggers defecation reflex

32. Mass Movement

33. Defecation Defecation Reflex initiated when rectal walls stretch ß
parasympathetic reflex
walls of the sigmoid colon and the rectum to contract & relaxation of the anal sphincter
External sphincter control is voluntary control
If defecation is delayed: the reflex stops until the next mass movement