Git Motility

8/13/2019 Git Motility

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GIT MOTILITY



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



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



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."



Propulsive movements : Peristalsis



(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



Segmentation movements of the small intestine



PHYSIOLOGY OF MASTICATION AND

SWALLOWING



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



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



MUSCLES OF M ASTICATION

1. Masseter

2. Temporalis

3. Medial Pterygoid

4. Lateral Pterygoid

5. Buccinator

6. Muscles of tongue(extrinsic & intrinsic)



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



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.



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



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



Hard palate

Food bolus

Pharynx

Tongue

1. BUCCAL PHASE



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



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.



Food bolus

Epiglottis - closes

over airways

Trachea

2. PHARYNGEAL

PHASE

Larynx

Soft palate closes

entry to nasopharynx



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 )



Food bolus

Epiglottis - open

Oesophagus

3. OESOPHAGEAL

PHASE



PERISTALSIS IN THE OESOPHAGUS

Food bolus

Muscle

contraction

Stomach

Gastroesophageal

sphincter relaxes



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.



APPLIED

1. Abolition of swallowing reflex

2. Aerophagia

3. Achalasia Cardia

4. Gastroesophageal Reflex Disease (GRD)

5. Dysphagia



PHYSIOLOGY OF GASTRIC

MOTILITY



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



Physiologic anatomy of the stomach



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



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



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.



ChymePyloric sphincter

closed

Duodenum

1st peristalticwave

GASTRIC EMPTYING



2nd peristaltic

wave

Pyloric sphincter

opens

Chyme enters

duodenum

GASTRIC EMPTYING

Antral systole



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.



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



# 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



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



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



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



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.



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



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.



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



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



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



2 types Eccentric[A] & Concentric[B] contractions



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



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.



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



Function of the Ileocecal Valve



L ARGE INTESTINE



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)



Movements of large Intestine



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



.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



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



. 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



‘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

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