Movements of intestine:their mechanism,function and regulation.

1. Dr Prafull H Turerao.
Dr D.Y.Patil Medical College, Kolhapur
Tutor, Department of Physiology

2.  There are two types movements of small
intestine i.e.
 segmentation movement and
 peristaltic movements

3.  Segmentation movements – Distension of
small intestine with chyme stretches the
intestinal wall and initiates segmentation
movements.
 There are localized concentric contractions
(about 1-2 cm in length) spaced at intervals
along the intestine. They divide the intestine
into spaced segments.

4.  These contractions force the chyme back
towards the stomach and towards the colon
and last for 5-6 seconds.
 When muscle relaxes, chyme comes back to
the area from which it is displaced.

5.  A new set of contractions then begins at new
points between previous contractions.
 Segmentation movements occur at a rete of
8-12 min.
 Maximum frequency is present in duodenum
(12/min) and proximal jejunum. In terminal
ileum it is 8 to 9/min

6.  Functions – Segmentation contractions move
the food back and forth as explained above.
 This enables chyme to become thoroughly
mixed with the digestive juices and to make
proper contact with the absorptive surface of
the intestinal mucosa.

7.  Higher frequency of segmentation in
proximal intestine than in distal intestine
propels the chyme slowly towards the colon.

8.  Control – The segmentation contractions can
occur only if the slow waves (basic electrical
rhythm) produce action potential.
 Action potential appears on slow waves when
the membrane potential is sufficiently
depolarized.

9.  Frequency of segmentation is directly related
to the frequency of slow waves and is
controlled by pacemaker cells of small
intestine.

10. But segmentation contractions become very
weak on blocking the nervous system by
atropine.
Contractions are not really effective without the
background excitation by enteric nervous
system (especially myenteric plexus) though
slow wave in smooth muscle control the
segmentation contractions.

11.  Slow wave amplitude is also increased by
hormones, gastrin, cholecystokinin, motilin
and insulin.
 Secretin and glucagon reduce the slow wave
amplitude.

12.  Peristalsis is a wave of contraction precede by
wave of relaxation. Peristaltic wave can be
initiated in any part of the small intestine.

13.  It moves anal ward at a rate of 0.5-2 cm/min
but it is weak and dies out after travelling
only 3-5 cm very rarely up to 10 cm.
 So net movement of chyme in anal ward
direction is slow (1cm /min)

14.  Functions – Peristaltic waves propel the
chyme in anal ward direction.
 As chyme enters the intestine, it spreads
along the entire length of intestine due to
peristaltic waves for proper digestion and
absorption.

15.  Control – Peristaltic wave is controlled by
 nervous and
 hormonal factors.

16.  Nervous control – Peristalsis on the small
intestine increases immediately after meals
due to gastroenteric reflex.
 Distension of stomach due to meal initiates
this reflex.
 Impulses pass through myenteric plexus
from stomach to the small intestine along the
wall of small intestine causing increase in
peristaltic activity.

17.  Hormonal control – Gastrin , cholecystokinin,
insulin and serotonin enhance the intestinal
motility.
 Secretin and glucagon decrease the motility.

18.  Intense irritation of intestinal mucosa causes
very powerful and rapid peristalsis called
peristaltic rush. It is partly initiated by
extrinsic nervous reflex and partly by
myenteric reflex.

19.  Powerful peristaltic contractions travel long
distances in small intestine within minutes.
 It sweeps the contents of intestine into the
colon and relieves small intestine of either
irritative chyme or excessive distension.

20.  Ileocecal valve prevents back flow of faecal
contents from colon into the intestine. The
valve usually resists pressure of 50-60 cm of
water.
 Immediately preceding the ileocecal valve, the
wall of ileum for several centimetre has a
thickened muscular coat which is called
ileocecal sphincter.

21.  Tonic contractions of this sphincter slows
emptying of meal contents into the caecum.

 The contents stay in the ileum for long time
which facilitates absorption.
 Gastroileal reflex and gastrin cause relaxation
of ileocecal sphincter. Its degree of
contraction is also controlled by reflexes from
caecum

23.  There are two types of movements of large
intestine namely haustral contraction and
mass movement. Their functions are to
increase the efficiency of colon for water and
electrolytes absorption and promote
excretion of faecal matter.

24.  Haustral contractions are similar to
segmentation movements of small intestine.
Large circular bands of constriction occur at
regular intervals. At each of these constrictive
points 2.5 cm of circular muscle contracts.
Longitudinal muscles (tineae coli) also
contract. This causes unstimulated portions
of large intestine to bulge in a bag like sacs
called haustrations.

25.  Mass movements only occur 3-4 times a day.
They are just like peristalsis of small
intestine. Much propulsion of faecal matter in
caecum and ascending colon results due to
haustral contractions.

26.  From beginning of transverse colon to the
sigmoid colon mass movements cause
propulsion.
 Mass movements are initiated after breakfast
or meal due to gastrocolic or duodenocolic
reflexes, initiated by distension of stomach or
duodenum.

27. First constrictive ring appears at irritated point
(usually transverse colon), then about 20 cm
colon distal to it contracts as a unit forcing
faecal matter in this segment down the colon.
Relaxation occurs within 2-3 minutes.

28.  Then mass movement is initiated at the next
point. Usually mass movements once initiated
persist for about 10-30 minutes.
 Irritation of colon can also initiate mass
movements. When mass movements force the
faecal matter into the rectum, desire for
defecation is felt.

29.  Process by which faecal matter is excreted is
called defecation. Usually the rectum is
empty. Due to mass movements, faecal
matter enters the rectum causing distension.

30.  A recto sphincteric reflex relaxes the anal
sphincter and generate urge to defecate.
 Defaecation involves both voluntary and
reflex activity. Ordinarily defaecation is
initiated by defaecation reflexes as follows.

31.  Intrinsic reflex – It is mediated by intrinsic
nerve reflex. Distension of rectum with faeces
initiates afferent signals which pass through
myenteric plexus to descending colon to
initiate a peristaltic wave.

32.  As peristaltic wave approaches lower end of
rectum it causes relaxation of internal anal
sphincter (made up of smooth muscle).
 If external sphincter is relaxed ( which is
made up of skeletal muscle and is under
voluntary control) defaecation occurs.

34.  Spinal cord reflex – Intrinsic reflex is weak
and is reinforced by this reflex. Distension of
rectum due to faeces causes transmission of
signals to sacral segments of spinal cord.

35.  Signals are transmitted from here through
pelvic nerves ( parasympathetic fibres) to
colon to intensify the peristaltic waves and
relaxation of inner anal sphincter.
 It converts intrinsic defaecation that results
into emptying of large bowel from splenic
flexure to anus

36.  In addition to defaecation reflexes, the
abdominal muscles and diaphragm contract
increase the intra abdominal pressure forcing
the faeces through the anal canal.
 Defaecation can be prevented by voluntarily
contracting the external anal sphincter.

37.  If defaecation does not occur, internal anal
sphincter closes, rectum relaxes to
accommodate faecal matter within it.
 In new-born babies or in person with
transected spinal cord, defaecation reflex
causes automatic emptying of lower bowel
without normal voluntary control on external
anal sphincter

38.  Movements of small intestine
 Segmentation movements
 Peristaltic movements
 Peristaltic Rush
 Movements of Large intestine
 Haustral contractions
 Mass movement of large intestine
 Defaecation reflex

39.  Textbook of Medical Physiology – Guyton
And Hall 13th Edition
 Textbook of Physiology – A K Jain 6th Edition
 Medical Physiology For Undergraduate
Students – Indu Khurana
 Net Sources Images.

40. Thank You