Post on 04-Jun-2018
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GIT MOTILITY
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The GIT motility refers to the movements for :-
1. Mechanical breakdown of food
2. Mixing & circulating the GI contents
3. Propel food along the length of the tract from the
mouth to the anus
GIT motility is determined by :
1. Properties of smooth muscle
2. Neural input
3. Endocrine & paracrine factors
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Electr ical Activity of Gastrointestinal Smooth Muscle
- Oscillating RMP : -65 to -45 mv ( Na pump activity)
-Comprise of : Slow waves (BER from 3-12/min) & Spikes (Ca-Na
channels & K channels)- Interstitial cells of Cajal →act as electrical pacemakers
- Acts as syncytium due to presence of gap junctions
- Determines the rhythm of most GI contractions
4. Hormones
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FUNCTIONAL T YPES OF MOVEMENTS IN GIT
2 types:
(1) Propulsive movements :
They cause food to move forward along the tract at an appropriate
rate to accommodate digestion and absorption.
Peristalsis → contraction ring along with receptive
relaxation
Stimuli : distention of the gut , chemical/ physical irritation
Myenter ic plexus is necessary for peristalsis.
The myenteric reflex or the peristalt ic reflex plus the anal
direction of movement of the peristalsis is called the "law of
the gut."
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Propulsive movements : Peristalsis
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(2) Mixing movements :
They keep the intestinal contents thoroughly mixed at all times.
Peristaltic contraction : against closed sphincter results in
churning .
Local intermittent constrictive contractions occur every few
centimeters in the gut wall.
last only 5 to 30 seconds;
then new constrictions occur at other points in the gut.
Thus "chopping" and "shearing" the contents .
Like segmentation
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Segmentation movements of the small intestine
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PHYSIOLOGY OF MASTICATION AND
SWALLOWING
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INGESTION OF FOOD
The amount of food that a person ingests is determined
principally by intrinsic desire for food called hunger.
The type of food that a person preferentially seeks is
determined by appetite.
Ingestion involves :-
1. Placement of food in mouth
2. Mastication
3. Lubrication
4. Swallowing
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M ASTICATION/CHEWING
Refers to process by which the food placed in mouth is
cut and grounded into smaller pieces.
It involves :-
1. Action of teeth
2. Movement of jaws
3. Co-ordinated movements of tongue
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MUSCLES OF M ASTICATION
1. Masseter
2. Temporalis
3. Medial Pterygoid
4. Lateral Pterygoid
5. Buccinator
6. Muscles of tongue(extrinsic & intrinsic)
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CHEWING REFLEX
Mastication → voluntary act → coordinated by chewing
reflex → opening & closing of jaw.
Opening of mouth for food→ stretch reflex → closure.
Food particles →buccal receptors→ reflex inhibition of
muscle of mastication & reflex contraction of digastric with
lateral pterygoid→ opening.
Tongue moves the food between the upper & lower jaw
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FUNCTIONS OF MASTICATION
1. Breaking of food into smaller pieces increases the total surfacearea.
2. Undigestive cellulose membrane present around the nutrition
portion of most fruits and raw vegetables is broken, making it
easier for them to be digested.
3. Lubricates food by mixing it with salivary mucus
4. Mixing of food with saliva initiates the process of starch and
lipid digestion
5. Swallowing becomes easy
6. Eating becomes pleasurable.
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DEGLUTITION (SWALLOWING)
It refers to passage of food from the oral cavity into stomach.
It is facilitated by the secretion of saliva and mucus and
involves the mouth, pharynx, and esophagus.
Swallowing occur s in thr ee stages :
1. the voluntary stage,(Buccal phase ) in which the bolus is
passed into the oropharynx;
2. the pharyngeal phase , the involuntary passage of the bolus
through the pharynx into the esophagus;
3. the esophageal stage, the involuntary passage of the bolus
through the esophagus into the stomach
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BUCCAL /ORAL PHASE
It is voluntary phase.
First the tip of the tongue , and later the more posterior
portion of the tongue press against the hard palate.
The action of tongue moves the bolus upward and then
backward into the mouth.
The bolus is forced into oropharynx , where it stimulates
the touch receptors that initiates swallowing reflex
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Hard palate
Food bolus
Pharynx
Tongue
1. BUCCAL PHASE
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PHARYNGEAL STAGE (1-2 S)
It is an involuntary stage.
Swallow ing ref lex :-
The bolus stimulates receptors in the oropharynx, which
send impulses (Afferent via V ,IX ,X CN) to the
deglutition center (NTS ,N. Ambiguus ,Dorsal motor
nucleus) in the medulla oblongata and lower pons of the
brain stem.
Efferent via V,VII,IX,X,XII CN and C 1-3 goes to soft
palate ,uvula,pharyngeal musculature and the tongue
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1. Approximation of post. pillars of fauces
2. Soft palate & uvula is pulled upward and the
palatopharyngeal fold move medially.
3. The vocal cords are pulled together (deglutition
apnoea)
4. The larynx is moved forward and upward
5. Epiglottis swings over laryngeal opening, closing it.
6. The upper esophageal sphincter relaxes.
7. A peristaltic wave is initiated
8. Respiration is reflexly inhibited.
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Food bolus
Epiglottis - closes
over airways
Trachea
2. PHARYNGEAL
PHASE
Larynx
Soft palate closes
entry to nasopharynx
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OESOPHAGEAL PHASE
The food bolus is propelled from the upper part of the
esophagus to stomach by the esophageal peristalsis
and aided by gravity.
Esophageal peristalsis
1. Primary (initiated by swallowing)
2. Secondary ( stretching of mechanical receptors)
LES relaxes as peristalsis wave approaches .
( Receptive relaxation )
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Food bolus
Epiglottis - open
Oesophagus
3. OESOPHAGEAL
PHASE
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PERISTALSIS IN THE OESOPHAGUS
Food bolus
Muscle
contraction
Stomach
Gastroesophageal
sphincter relaxes
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LOWER ESOPHAGEAL SPHINCTER
LES is tonically active but relaxes on swallowing.
The tonic activity prevents reflux of gastric contents into the
esophagus.
LES is made up of 3 components :
1. The esophageal smooth muscle is more prominent at the
junction with the stomach (in t r ins ic sph incter) .
2. Fibers of the crural port ion o f the diaphragm , a skeletal muscle,
surround the esophagus at this point (extr insic s ph incter) and
exert a pinchcock-like action on the esophagus.
3. The obl ique or sl ing f ibers of the stomach wal l create a flap
valve that helps close off the esophagogastric junction and prevent
regurgitation when intragastric pressure rises.
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APPLIED
1. Abolition of swallowing reflex
2. Aerophagia
3. Achalasia Cardia
4. Gastroesophageal Reflex Disease (GRD)
5. Dysphagia
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PHYSIOLOGY OF GASTRIC
MOTILITY
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Major function of Gastric motility
1. Allow stomach to serve as reservoir for large
volume of food .
2. Break food into smaller particle & mix food with
gastric secretions to form chyme
3. To empty gastric contents into duodenum at
controlled rate
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Physiologic anatomy of the stomach
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T YPES OF GASTRIC MOTILTY
Related to meal
1. Recep tive Relaxation
Distention of esophagus during swallowing evokes relaxation
of stomach via vagovagal reflex
Oral region relaxes to accommodate ingested food without
increase in intraluminal pressure.
Stretch Receptors produces further relaxation
Vagovagal reflex with NO,VIP & CCK of plays imp. Role
for Receptive relaxation
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2. Mixing persistaltic waves
Food in stomach week per istaltic constr ictor waves or mixing waves
begin
mid portion & move towards antrum (3-4/Min.) I ni tiated by BER & consists of electrical “slow waves ”
As constrictor waves progress from body into antrum become intense
& provide powerful per istalti c constr ictor r ings
Force antral contents under high pressure towards pylorus
Constrictor rings also play important role in mixing
most of antral contents squirted backward through peristaltic ring
towards body of stomach Retropulsion moving peristaltic constrictor rings combined with
squirting action
at this point partly digested food is semisolid mass called chyme
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3. Gastric Emptying
Food in the stomach is normally emptied into the duodenum within
4 hours of ingestion .
Chyme is propelled towards the pyloric sphincter by vigorous
peristalsis.
1. I ntense Antral Peristalti c Contractions – “Pyloric Pump”
2. Role of the Pylorus in Controll ing Stomach Emptying + Antral
Systole
With each wave about 2-5ml of chime is released into theduodenum before the sphincter closes again.
The rest of the chyme tumbles back and is propelled forward again
with the next wave of peristalsis.
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ChymePyloric sphincter
closed
Duodenum
1st peristalticwave
GASTRIC EMPTYING
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2nd peristaltic
wave
Pyloric sphincter
opens
Chyme enters
duodenum
GASTRIC EMPTYING
Antral systole
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REGULATION OF GASTRIC EMPTYING
It depends on the :
1. Type of food ingested :
Food rich in carbohydrate leaves the stomach in a few hours.
Protein-rich food leaves more slowly, and emptying is slowest
after a meal containing fat
2. Osmotic pressure of the material entering the
duodenum.
Hyperosmolal i ty of the duodenal contents is sensed by
"duodenal osmoreceptors" that initiate a decrease in
gastr ic emptyin g which is probably neural in origin.
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POWERFUL DUODENAL FACTORS THAT INHIBIT
STOMACH EMPTYING
Inhibitory Effect of Enterogastric Nervous Reflexes from the
Duodenum ( ENS, Symp. , Vagus)
Factors affecting are :
1. Degree of distention of the duodenum
2. The presence of any degree of irritation of the duodenal mucosa3. degree of acidity of the duodenal chyme
4. degree of osmolality of the chyme
5. The presence of breakdown products of fats > Carbohydrate > proteins
Hormonal Feedback from the Duodenum Inhibits Gastric
Emptying : CCK , Secretin ,GIP
Applied : Dumping syndrome
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# Related to Empty stomach
1. Migrating motor complexes
Soon after stomach emptied between meals mild peristaltic
contractions begin by migrating motor complexes [MMC] in body of
stomach gradually over periods of hours to ileum
MMCs are initiated by motilin, migrate aborally at a rate of about 5
cm/min, and occur at intervals of approximately 90 min
Serve to clear the stomach and small intestine of luminal contents in
preparation for the next meal
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2. Hunger contractions
When the stomach has been empty for several hours
They are rhythm ical per istal t ic contract ions in the body of the
stomach.
When the successive contractions become extremely strong ,
often fuse together to cause a continuing tetanic contractionlast for 2-3 m in
The person sometimes experiences mild pain in the pit of the
stomach, called hung er pangs .
Hunger contractions more intense in young & healthy with
high degree of gastrointestinal tonus
by low level of blood sugar
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VOMITING (EMESIS)
It is the forcible expulsion of the contents of the upper GItract (stomach and sometimes duodenum) through the
mouth.
It is preceded by a - nausea, salivation
- rapid or irregular heartbeat /
breathing
- dizziness, sweating
- pallor, and dilation of the pupils
- reverse peristalsis/antiperistalsis
- retching
Neural pathways leading to the initiation of vomiting
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Neural pathways leading to the initiation of vomiting
in response to various stimuli
Symp
V,VII,IX,X,X
II, spinal
nerves
Motor
impulses to
UGIT
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PROGRAMMED VOMITING RESPONSE
Ejection Phase
Involves several preprogrammed coordinated smooth and striated
muscle responses.
Abolition of intestinal slow-wave activity
Start of retrograde contractions
Vomiting Act
(1) a deep breath,
(2) raising of the hyoid bone and larynx to pull the upper esophageal
sphincter open,
(3) closing of the glottis to prevent vomitus flow into the lungs, and
(4) lifting of the soft palate to close the posterior nares.
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5. Contraction of abdominal and inspiratory muscles
against a closed glottis.
6. ↑ in intra-abdominal pressure & ↓ in intrathoracic
pressure
7. Relaxation of the diaphragmatic crural muscle and LES
8. Expulsion of the gastric contents into the esophagus
and hence through the mouth
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DISORDERS OF THE STOMACH
1. Gastritis-Inflammation of the Gastric Mucosa
2. Peptic ulcer :
It is an excoriated area of stomach or intestinal mucosa caused
principally by the digestive action of gastric juice or upper small
intestinal secretions.
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MOVEMENTS OF SMALL INTESTINE
I. During interd igest ive per iod
- Migrat ing Motor Complexes (MMC)
Between meals mild peristaltic contractions begin in body of
stomach gradually over periods of hours → ended in ileum
MMCs are initiated by motilin, migrate aborally at a rate of about 5
cm/min, and occur at intervals of approximately 90 min.
Funct ion as ho usekeeper
1. Serve to clear the stomach and small intestine of luminal
contents in preparation for the next meal.
2. Keep upper gut free of bacetria
3. Help in circulation , GI secretion
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II. During digest ive per iod
1. Mixing movements :
- Segmentat ion contract ions ( rhythm ic / ir regular)
- Ring like contractions appear a regular interval along gut
involving a localized ‘segment’ of 1-2cm & then relaxes
- Have the appearance of a chain of sausages
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By these movements food is divided [segmented] & mixed
together with digestive juices thoroughly [again & again]
→slows transit time → ↑ contact time with absorptive area.
No net mo vement in a part icu lar direct ion
sequence of segmental contraction
2 types Eccentric[A] & Concentric[B] contractions
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2 types Eccentric[A] & Concentric[B] contractions
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Control of Rhythmic segmental contractions
I ni tiated by pacemaker cells located in 2nd part of duodenum near
entry of common bile duct
a BER of „slow wave ’ can be demonstrated is conducted caudally by
longitudinal muscle layer & coordination is via myenteric plexus
Frequency is directly related to frequency of „slow waves‟ in itiated by
pacemaker cells & less inf luenced by neural or circulating hormones
Strength of contraction = f requency of spike generated by „slow waves‟ .
Strength ↑ by : Gastrin ,Motil in, CCK, I nsul in ,serotonin
↓ by : secretin , glucagon
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2. Propulsive movements
Peristalsis : refers to wave of contraction followed by wave of
relaxation
- Stretching or distention of intestinal wall chyme
Circular constr iction forms above due to contraction of circular
muscle layer while the lumen below is dilated due to contraction of
longitudinal muscle layer ( receptive relaxation ) so intestinal
contents move towards dilated part .
- Worm like vermicular or peristaltic movements
- Control : neural & hormonal
Per istalsis Rush :
- Refers to powerful peristaltic contractions which occurs when
intestinal mucosa is irritated.
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Function of peristalsis propel intestinal content towards ileo-cecal
valve.
duration of wave 1-2cm/sec
Stimulus for peristalsis local stretch release serotonin & this activates
sensory neurons stimulate Myenteric plexus & response knows as
Myenteric Reflex
Ach & substance P released circular constriction
NO ,VIP & ATP below the point of stimulus relaxation
strong emotions via vagal can muscular contraction & tone of SI
anger ,fear & pain via splanchnic nerves muscular contraction &
tone of SI
Adynamic ileus or Paralytic i leus
.Mechanical obstruction of SI localized mechanical obstruction of SI
severe cramping pain intestinal colic
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Function of the Ileocecal Valve
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Function of the Ileocecal Valve
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L ARGE INTESTINE
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FUNCTIONS OF THE LARGE INTESTINE
1. Haustral churning, peristalsis, and mass peristalsis drive
contents of colon into rectum.
2. Bacteria in large intestine convert proteins to amino acids,
break down amino acids, and produce some B vitamins
and vitamin K.
3. Absorbing some water, ions, and vitamins.
4. Forming feces.
5. Defecating (emptying rectum)
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Movements of large Intestine
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g
.Most of contractions of cecum & proximal part of large intestine
are segmental & are effective at mixing & circulating
colonic contents than propelling
.mixing action facilitates absorption of salts & water by mucosal
epithelium
.localized segmental contractions divide colon into ovoid segments
called haustra & segmentation in colon haustration
Prominent haustral pattern
HAUSTRAL CONTRACTIONS
Food
residue
Haustra
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.In proximal colon antipropulsive pattern predominant
. Reverse peristalsis & segmental propulsion toward cecum both
take place & so chyme retained in proximal colon & this
retention facilitate absorption of salt & water
Mass movements
.simultaneous contraction of smooth muscle occurring at same time
over a large portion of colon & occur in descending & sigmoidcolon ,lasts 3-4 min with pressure rising steeply to peak up to
100 cm saline & decline slowly
Gastrocolic reflex
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Control of colonic Motility
As in other segments of GIT intramural plexus directly control
contractile behavior of colon
Extrinsic innervations modulate
.Enteric stimulatory motor neurons use Ach & substance P as
neurotransmitter
.Enteric inhibitory neurons release VIP & NO onto colonicsmooth muscle
.Extrinsic autonomic nerves to colon modulate control of colonic
motility by enteric nervous system
.R eflex control of colonic motilitygastrocolic reflex
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. Certain
Physiological
events,as arising
[orthocolic reflex ] &
ingestion of food
[gastrocolic &
gastroileal reflexes]
,may initiate a mass
peristalsis propelling
fecal bolus into
rectum
Gastroileal
reflex may be
mediated viavagus or via
intrinsic
nerves or both
Gastrocolic reflex may be
mediated via pelvic splanchnic
nerves or via intrinsic nerves as
continuation of gastroileal
reflex, or both
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‘Awareness of
urge,correlated with
visual & auditory
stimuli,plus memory
& habit ,cause
individual to seek
out toilet & makeother appropriate
preparations &
simultaneously
cause
Voluntary contraction of external
sphincter & levator ani muscles [via
pudendal & levator ani nerves] to retain
Stimulation of rectal stretchreceptors sends afferent
impulses to spinal cord[for
local reflexes] & thence to
brain[ for awareness of urge]
Local autonomic reflexes [via
pelvic splanchnic nerves] cause
contraction of rectal
musculature & relaxation of
internal sphincter in effort to
expel feces