Physiology gastroenterology 3&4.

1. Gastrointestinal physiology
GIT Movements:
Transport & mixing of food in the GIT:
Dr.M.A.M.Shaikhani.

2. Food ingestion: Stimulated by hunger & Appetite.
Mastication
swallowing.
Mastication(chewing):
• By incisors & molar teeth controlled by:
• Chewing reflex: stimulated by bolus presence in the mouth
causing reflex inhibition of mastication muscles , lower jaw drops
& initiating a stretch reflex of jaw mastication muscles leading to
their rebound contraction & repeating again the same series of
events until the bolus in fully masticated for easy swallowing.

3. Importance of chewing:
1.Exposing the total surface area of foods specially the raw
vegetables to GIT secretions & enzymes.
2.Prevents excoriation of GIT mucosal surfaces.
3.Increasing the easy passage of well lubricated food from
esophagus to stomach& to the s.intestine.

4. Swallowing process (deglutition)

7. The Swallowing Process

8. Swallowing(deglutition).
Of 2 stages:
1.Volantary oral stage : involve the tongue & hard palate
as the tongue queezes the food & rolles it posteriorly into the
pharynx by upward & backward pressure against the hard
palate.
2.Automatic(involuntary) stage :I t is automatic & can not be
stopped voluntarily. of 2 stages:
1.Pharyngeal stage . 2.esophageal stage.

9. 1.Pharyngeal stage:
The food enters the pharynx stimulates the swallowing receptors
around the pharyngeal opening & impulses pass to the brain
stem to initiate a series of automatic pharyngeal contractions as
follows by 4 stages:
A. Soft palate is pulled upward to close the
posterior nares to prevent food regurgitation into the nose(as it
occurs in palatal palsy due to 9th
& 10th
cranial nerve palsy. )
B. Palatopharyngeal folds
on either sides are pulled medially to approximate each other
forming a narrow sagital slit through which the food must pass
into the posterior pharynx allowing the passage of only well
masticated bolus ( lasts < 1 second.)

10. 1.Pharyngeal stage:
C. Strong approximation of laryngeal vocal cords with the backward
swinging of epiglottis(due to the presence of a ligament which
prevent its upward movement ),blocks the opening of larynx/trachea
preventing passage of food bolus into the trachea & so preventing
suffocation .The vocal cords & larynx are more important than
epiglottis as laryngeal or vocal paralysis causes strangulation while
removal of epiglottis usually dose not cause serious disability in
swallowing.
D. Upper 3-4 cms. Of esophagus forms the pharyngeo-esophageal
sphincter or upper esophageal sphincter( UES) (remains tonicly
contracted between swallowings to prevents air swallowing into
esophagus & stomach during respiration), become relaxed during
this stage by the upward movement of larynx& also the entire
pharynx contracts allowing easy movement of food from posterior
pharynx into the upper esophagus.

11. • Whole pharyngeal stage lasts for 1-2 seconds ,during this short
period the respiration is stopped & is hardly noticeable
• During this the swallowing center inhibits the respiratory center
of medulla preventing respiration& allowing swallowing to
proceed without serious affection of respiration.

12. Neuronal control of pharyngeal stage of swallowing:
• It is a reflex act & not controlled by higher brain centers.
• Sensory divisions of trigeminal & glosopharyngeal cranial nerves
transmit impulses from the most sensitive areas of the pharynx
(ring around the pharyngeal opening & the tonsillar pillars) to a
center in the medulla oblongata called tractus solitarius (sensory
swallowing center).
• The successive stages of swallowing are automatically controlled
by the motor division; a neuronal area throughout the reticular
substance of medulla& lower pons (motor swallowing or
deglutition center).
• The motor impulses from this center pass to the pharynx& upper
esophagus through 5th,9th,10th & 12th
cranial nerves & by few of
the superior cervical nerves .

13. 2. esophageal stage of swallowing:
• Esophagus conducts food from pharynx to the stomach by
peristaltic movements .
• Normally it has 2 types of peristaltic movements(PMs):
• 1.primary PMs: is continuation of the PMs that begins in the
pharynx & spreads to the eso. During eso. Stage of swallowing &
pushes the food from pharynx to the stomach in 5-8 seconds
helped by gravity.
• 2.Secondary PMs : starts when the primary PMs fails to move all
the food from the eso. Causing distention of the eso.initiating
secondary PMs.

14. Neuronal control of eso. Stage:
• The pharyngeal & upper 1/3 esophageal muscles are striated
responsible for PPMs controlled only by skeletal motor nerve in
the glossopharyngeal & vagi ,while the lower 2/3 of esophagus is
smooth muscles supplied by the myenteric aurbach plexus
controlled by PS fibers of the vagi & can be excited even when
vagi are sectioned (as in operations for peptic ulceration) &
function independently of vagi supporting secondary PMs helping
to push food to the stomach helped by gravity.
• Secondary PMs are initiated partly by the intrinsic neuronal
circuit in the esophageal myenteric plexus & partly by the vagi
afferent & efferent fibers .

16. Swallowing Summary:
– Begins as a voluntary activity.
– Completed as an involuntary activity
– Involves Mouth, pharynx & esophagus.
• Oral phase is voluntary.
• Pharyngeal & esophageal phases are involuntary.
– Larynx is raised.
– Epiglottis /vocal cords covers the entrance to
respiratory tract.
– Involuntary muscular contractions & relaxations are
coordinated by the swallowing center in the medulla
which acts in cooperation with respiratory center to
stop respiration during pharyngeal stage to prevent
suffocation.

17. MCQs:
Chewing of food:
A.Controlled by reflex.
B.Mixes food with enzymes.
C.Mixes food with secretions.
D.Makes the food to hurt GIT mucosa.
E.Make the food to pass more easily.

18. MCQs:
Swallowing process:
A.All stages are involuntary.
B.The hard palate plays a role in the
pharyneal stage.
C.Soft palate plays a role in the oral phase.
D.The pharyngeal stage is shorter than
esophageal stage.
E.The upper esophageal sphincter is closed
during normal respiration.

19. MCQs:
Relation between swallowing & breathing:
A.Breathing stops in all stages of swallowing.
B.Breathing stops in all pharyngeal phases.
C.There is reflex inhibition between
swallowing & respiratory centers.
D.Cessation of breathing during some
pharyngeal phases is consious.
E.The upper esophageal sphincter is closed
during respiration to prevent passage of air
into the stomach.

20. MCQs:
Peristaltic movements of esophagus:
A.Primary peristalsis is done by skeletal &
smooth muscles.
B.Food moves down usually by primary &
Secondary peristalsis is always present.
C.Secondary peristalsis is always supported
by Aurbach plexus.
D.Gravity helps both primary & seconday
peristlsis.
E.Peristalsis does not occur without vagus
nerve.

21. The antireflux mechanisms of lower esophagus:
• 2 important mechanisms in the lower eso allows smooth easy
passage of food to the stomach & prevent reflux of acidic stomach
contents into the lower eso. Causing reflux acid esophagitis :
• 1. Muscle of the lower 2-5 cms. Of eso. Above its junction with the
stomach is anatomically not different from the rest of eso. But it
is slightly thickened & function as lower eso, shpincter(LES).It
remains tonicly contracted between swallowings to prevent reflux
but in some pathological conditions it is lax causing reflux
esophagitis & in other pathological states it fails to relax during
eso. Stage of swallowing causing type of dysphagia called
achalasia.
• 2. Short portion of eso. below the diaphragm before reaching the
stomach has a valve like action as it become curved during any
increased intra-abdominal pressure as coughing,straining or
hard breathing so preventing reflux of acidic stomach contents
into lower eso

22. The antireflux mechanisms of lower esophagus:
Pregnancy
Large meals
Overweight
Bending
Tight clothing
Smoking (relaxes
sphincter)

23. EsophagusEsophagus FundusFundus
BodyBody
AntrumAntrum
PyloricPyloric
SphincterSphincter
DuodenumDuodenum

25. Motor functions of stomach:
• The stomach consists of:
• 1. body(corpus). 2.Antrum. 3.Fundus ( physiologically a part of
body but anatomically a separate part)
• The main motor functions of stomach are:
• 1.storage of food: By receptive relaxation of proximal stomach to
accommodate with large quantities of food entering the stomach
up to about 25 liters facilitated by vagogal reflexes.
• 2.Mixing & propulsion of food :
• by mixing or constrictor waves which moves towards the antrum
along the stomach wall & occurs every 20 seconds( initiated by
basic electrical rhythm BER consisting of electrical slow waves)
causing mixing of food with secretions & provide weak propulsion
to move food forwards towards the antrum.it starts near the mid
point of stomach when it is full & higher up & stronger when it
not full to push the last amount of stored food into the antrum&
when completely empty the stomach become quiescent until new
food enters.

26. • The real mixing occurs when the peristaltic waves of stomach
passing along the antrum towards the pylorus ,is opposed by the
impeding action of pyelorus which allows the passage of only few
mls.of well digested food to pass to the duodenum.This two
opposing forces allows the PMs to dig deeply into the antral
contents causing mixing of stomach contents to form a paste like
substance called chyme.
• With each gastric PM the pylorus opens partialy to allow
passage of only well digested liquidly chyme food.

27. 3.Emptying of the stomach:
• Facilitated by the pyeloric pump which consists of the PMs of the
stomach & opening of the pyelorus:
• Regulation of stomach emptying & pyeloric pump:
• By stomach & duodenal factors:
• Stomach factors or signals:
1. Distension of stomach by food stimulates
gastric emptying.
• 2.Gastrin hormone :released by antral mucosal in response to
presence of certain type of food leading to increase PMs &
inhibits pyloric tone facilitating gastric emptying.
• Duodenal factors or signals: inhibiting pyeloric pump & gastric
emptying,include:
• 1. Distention of duodenum 2. acidity of duodenal mucosal.
• 3. chyme osmolarity. 4. irritation of duodenal mucosal.
• 6.Certain chyme breakdown products specially protein & to
lesser extent fat.
• 7.Duodenal hormones that inhibit gastric emptying include
mainly cholycystokinin (CCK) stimulated mainly by fats entering
the duodenum ,less important include: secretin &gastric
inhibitory peptides(GIP).

28. Mechanical Processes: Mixing and EmptyingMechanical Processes: Mixing and Emptying
PyloricPyloric
SphincterSphincter
(open)(open)
DuodenumDuodenum
FundusFundus
BodyBody
AntrumAntrum 3. A small amount3. A small amount
of chyme isof chyme is
pushed intopushed into
the duodenum.the duodenum.
2. Most mixing2. Most mixing
occurs in theoccurs in the
antrum.antrum.
ChymeChyme
Food
PeristalticPeristaltic
WavesWaves
1. Peristaltic Waves1. Peristaltic Waves
begin in thebegin in the
fundus.fundus.

29. Mechanical Processes: Mixing and EmptyingMechanical Processes: Mixing and Emptying
DuodenumDuodenum
4. When the4. When the
peristaltic waveperistaltic wave
reaches thereaches the
pyloric sphincterpyloric sphincter
it closes.it closes.
PyloricPyloric
SphincterSphincter
(closed)(closed)
ChymeChyme

30. Mechanical Processes: Mixing and EmptyingMechanical Processes: Mixing and Emptying
DuodenumDuodenum
4. When the4. When the
peristaltic waveperistaltic wave
reaches thereaches the
pyloric sphincterpyloric sphincter
it closes.it closes.
PyloricPyloric
SphincterSphincter
(closed)(closed)
5. The remainder5. The remainder
of the chyme isof the chyme is
propelledpropelled
backwards.backwards.
ChymeChyme
6. The next wave6. The next wave
of peristalsisof peristalsis
pushes the chymepushes the chyme
forward again.forward again.

31. DuodenumDuodenum
PyloricPyloric
SphincterSphincter
(closed)(closed)
ChymeChyme
Factors in theFactors in the DuodenumDuodenum that Influencethat Influence
the Rate of Gastric Emptyingthe Rate of Gastric Emptying
1. Fat1. Fat
3. Hypertonicity3. Hypertonicity
2. Acid2. Acid
4. Distention4. Distention

32. Hunger contractions or pangs:
• Rhythmical PMs in the body of stomach, when empty for long
time & they become extremely strong & fuse together to cause
tetanic contractions lasting for 2-3 mins. associated with pain. It is
more intense in young persons with high degree of GIT tone &
greatly increase during low blood sugar.

33. Movements of the small intestine(SI):
• Of 2 types:
• 1.Mixing or segmentation contractions: stimulated by stretching
of SI by chyme, are localized concentric contractions spaced at
intervals , each travel only about 1cm. &when one set relaxes
another set begins forming chain of sausages.They mix the chyme
in a frequency of 8-12/min.backed by enteric NS specially the
myenteric plexus.
• 2.Propulsive or peristaltic movements: move anal wards much
faster proximally than distally. Of a frequency of ½-2
cms./seconds so it needs 3-5 hours for the passage of chyme from
the pylorus to the ileo-cecal valve.
• Caused by cooperation of circular & longitudinal muscle layers.

35. Movements of the small intestine(SI):
Control of SI PMs:
• By nervous & hormonal factors .
• They increase after a meal through the myenteric plexus by a
reflex called the gastroenteric reflex
• Hormonal factors that increase PMs include CCK& serotonin &
those inhibiting PMs include : secretin & glucagons.
• In the ileo-cecal (IC) valve the chyme is blocked for several hs
until the person eats another time when a new GE or GI reflex
intensifies the peristalsis & pushes the chyme to the cecum.

36. Function of IC valve:
• Prevents the backflow of cecal or colonic contents into the SI
&resists a back pressure of 60 cms Water .
• Allows the emptying of ileal contents into the cecum after the
gastroileal reflex
• Backed by:
• Myenteric plexus
• Prevertebral sympathetic ganglia
• Hormone gastrin which increase ileal contractions & relaxes the
IC sphincter or valve
• About 1500 mls.of chyme empty into the cecum each day.

37. GE Reflux is prevented by:
• A. LES.
• B. Lower esophageal angulation.
• C. Diapgragmatic hiatus.
• D. Esophageal motility.
• E.Intragastric pressure.

38. GE Reflux is aggravated by:
• A. OBESITY.
• B. Bending.
• C. Smoking.
• D. Muscle relaxing drugs.
• E. Pregnancy.

39. Most of the peristaltic acitvity of
the stomach occur in:
• A. Proximal stomach.
• B. Distal stomach.
• C. Antrum.
• D. Fundus.
• E. All above.

40. Part of the GIT that have oblique
muscle layes is:
• A. Esophagus.
• B. Stomach.
• C. Deudenum.
• D. Ileum.
• E. Colon.

41. Part of the GIT in which the mixing & propulsive
movements occur together is:
• A. Esophagus.
• B. Stomach.
• C. Deudenum.
• D. Ileum.
• E. Colon.

42. Factors that enhance gastric emptying are:
• A. Stomach distension.
• B. Deuodenal distension.
• C.Gastrin.
• D. CCK.
• E.GIP.

43. Storage of food in stomach is:
• A. Done in distal stomach.
• B. Facilitated by vagovagal reflex.
• C. Can make the stomach to accept large
amount of food.
• D. Requires receptive contraction of
proximal stomach.
• E. Requires actively contracting stomach.