motility 1

8/13/2019 Motility 1

1/38

GI Motility Part 1

L-8


2/38

Learning objectives

Role of enteric nervous system (ENS) ingastrointestinal motility

Types of motility & their functions

Mastication

Deglutition

Motor functions of the stomach (Gastricperistalsis, gastric emptying,)

The mechanism of vomiting- causes,consequences of protracted vomiting


3/38

Learning outcomes

8.1 Briefly describe the function of ENS inGI motility

8.2 Briefly describe the mechanism ofdeglutition

8.3 Outline the basic physiologic

mechanism preventing or minimizinggastro esophageal reflux


4/38

Learning outcomes contd

8.4 State the basic physiologic defect inAchalasia

8.5 Briefly describe the motor functions of

the stomach

8.6 Briefly describe how gastric emptyingis regulated ?

8.7 Briefly describe the basic physiologicmechanism of vomiting


5/38

MASTCATION or Chewing

First mechanical process to which food is

subjected in the mouth. Its an voluntaryact.

Muscles of mastication are:

Masseter, internal and external pterygoids,temporal muscles and buccinator.

Movements of upper & lower jaw by thesemuscles bring about the apposition of two

rows of teeth, which grinds or breaks thefood. Tongue helps in rolling over thefood.


6/38

Purpose served by mastication

-solid, large food particles are broken &reduced to a size convenient forswallowing.

- helps to break the indigestible cellulosecovering in fruits & vegetables.

- chewing results in reflex salivation


7/38

- serves to mix food with saliva, so as tomoisten & lubricate & thereby facilitate act

of swallowing. - Helps to mix with digestive components

of saliva.

Physical act of chewing thus helps intaste, smell and appreciation of othersensory qualities of the food.

By mastication finally the bolus is formed.


8/38

DEGLUTITION

It is the act of swallowing. The passage of

bolus from the oesophagus to stomach. Process is complicated since pharynx

forms a common passage for both

respiration & food passage. Divided into 3 stages:

1. Oral Phase (voluntary)

2. Pharyngeal phase (involuntary)

3. Oesophageal phase (involuntary)


9/38

Deglutiion (act of swallowing)

Is a sequentially programmed reflex

Initiated voluntarily

Multiple responses triggered in a specifictimed sequence

Involves highly coordinated contraction of

several musclesSwallowing center located in the medulla

Receptors in the pharyngeal wall


10/38

Oral phase

When the bolus is ready for swallowing, it

is voluntarily squeezed or rolled posteriorlyinto the pharynx by pressure of thetongue upwards & backwards against the

hard palate.


11/38

Pharyngeal phase

As bolus enters posterior aspect of oral cavity,

around pharynx, receptors get stimulated &send impulses to medullary deglutition center,which initiates series of coordinated automaticpharyngeal muscle contractions.

Now the bolus can enter into nasal cavities,trachea or oesophagus. So first two entries hasto be blocked.

1. soft palate is pulled upwards to close theposterior nares, which prevents reflux of foodinto nasal cavities.


12/38

2. Vocal cords of the larynx are strongly

approximated, and larynx is pulledupwards & anterior by the neck muscles.

These actions cause the epiglottis to swingbackwards over the opening of larynx,which prevents entry of food into trachea.


13/38


14/38

3. Palatopharyngeal folds pulled medially

to approximate each other. These foldsform a saggital slit through which foodpasses, this selectively allows onlyproperly masticated food.

What is deglutition apnoea ?


15/38

4. Upward movement of larynx also pullsup & enlarges the opening of the

esophagus. At the same timepharyngoesophageal sphincter relaxes,thus allowing bolus to move freely into

oesophagus from pharynx.

5. Peristalsis starts in superior part of the

pharynx then spreads over downward.


16/38

Pharyngeal phase Tongue pressed

against hard palate Uvula elevated,

touches posteriorpharyngeal wall

Elevation of larynx Epiglottis swings

backwards

Closure of vocal

folds

Food prevented

from re-enteringmouth

Seals off nasalpassage

Food prevented

from re-enteringrespiratory passage


17/38

1 2

5

3

4

Tongue

Uvula

Bolus

Epiglottis

Laryngeal opening

Esophagus


18/38

Deglutition reflex Receptors: Pressure receptors on the

pharyngeal wall, especially onthe tonsillar pillars

Afferents: V, IX, X nerves

Center: Medulla oblongata (deglutition

centre)

Efferents: V, IX, X , XII nerves

Effectors: Muscles of tongue, pharynx,

larynx


19/38

Define Pristalisis

constriction behind the bolus andrelaxation appears in front of the boluswhich results in forward movement ofbolus (oral to aboral direction).


20/38

Peristalsis

constriction relaxation


21/38

Peristalsis

Stimulus: Stretch of the gut wall

Speed: variable 2-25cm /min

Regulation: enteric NS (myentric plexus) ismust, modulated by extrinsic nerves i.e

sympathetic inhibits & parasympatheticstimulates. Can be blocked by atropine.

Function: propulsion of chyme from oral to

aboral direction.


22/38

Oesophageal stage

Exhibits primary peristalsis, mostly continuationfrom pharynx , which passes all the way to

stomach. If it fails reaching stomach, sec peristalisis starts

from distended portion of oesophagus wherefood is retained.

Receptive relaxation of lower oesophagealsphincter(normally under tonic contraction withintramural pressure of 30 mm Hg) occurs aheadof the peristalitic wave, allows food to enter

stomach. Receptive relaxation of stomach also occurs.


23/38

Applied aspects

Gastro esophageal reflux disease (GERD)

Frequent reflux of gastric contents into esophagus,due to incompetence of LES (sphincter nothaving tone). Symptom is heart burn, & this isthe commonest cause of unexplained chest pain.

AchalasiaLES fails in receptive relaxation, so bolus gets heldup in esophagus.

Dysphagia

Difficulty in swallowing. Esophageal musclescontract in a uncoordinated manner, may be dueto neural disorders.


24/38

MOTILITY IN STOMACH

For purpose of describing movements

stomach is visualized to be consisting of 2parts- Orad (fundus & body), Caudad(lower part)

1. Receptive relaxation 2. Mixing & churning

3. Gastric emptying

All these observed when stomach is full.


25/38

Receptive relaxation

To receive bolus orad part of stomach

relaxes. Due to vagally mediated reflexwhen the bolus reaches LES.

Advantages of relaxation:

As digestive processes are slow , stomachcan act as reservoir, gets sufficient timefor digestive juices to act.

Intragastric pressure doesnt rise much ( if

increases gastroesophageal reflux willoccur).


26/38

2. Mixing & churning

These movements achieved by gastricperistalisis ( at a rate of 3/min) + closureof the pyloric sphincter.

Effects of these movements are-

Breaking down of coarse food chunks

Thorough mixing of gastric juice with food

Squirting of gastric chyme into duodenum(ejecting of small volume of chyme in thinspurt)


27/38


28/38


29/38

Enterogastric reflex: inhibitory reflex arisingfrom duodenum which prevents gastric

emptying 1. Degree of distension of duodenum

2. Degree of irritation of duodenum

3. Degree of acidity of duodenum(pH


30/38

Gastric motility disorders:delayed gastric emptying(gastroparesis), rapid gastric emptying (dumpingsyndrome.

Reasons of abnormally delayed gastric emptying:

1) Pylorus and duodenum may be obstructed by an ulceror tumor, or by something large and indigestible that

was swallowed. (2) The pyloric sphincter at the exit of the stomach may

not open enough or at the right times to allow food topass through. These reflexes depend on nerves thatsometimes become damaged.

(3) The normally rhythmic, 3/min contractions of thelower part of the stomach can become disorganized sothat the contents of the stomach are not pushed towardsthe pyloric sphincter


31/38


32/38

Rate of emptying stomach intoduodenum based on the type of food


33/38

Gastric peristalisis in empty stomach(Migrating myoelectric complex MMC)

Empty stomach remains quiescent for 75-90mins, after this a MMC develops.

MMC is a wave of depolarization which is

immediately followed by an wave of muscularcontraction (hunger contractions).

MMC sweeps the whole stomach, then travelsduodenum, rest part of intestine, terminates at

terminal part of ileum taking about 10 mins.Again stomach rests for 75-90 mins then the

MMC repeats.


34/38


35/38

Vomiting (emesis)

Oral expulsion of upper GI contentsresulting from contractions of the gut andmuscles of the thorax and abdomen.

Retrograde or reverse peristalsis


36/38

Causes of vomiting & mechanism

Poison ingestion (by irritation)

Increased intracranial tension (symptomof a disease)

Uremia ( effects on chemoreceptor triggerzone in medulla)

Impairment of gastric motility( increaseintragastric pressure).


37/38

Mechanism of vomiting in intestinalobstruction:

Aff input to vomiting center in medulla, reflexlysends efferent impulses to abdominal muscles &diaphragm

Retrograde peristalsis in stomach

Intragastric pressure increases

LES relaxes & vomitus ejected via esophagus(closure of glottis prevents aspiration of

vomitus)


38/38

Consequences of Protractedvomiting:

Dehydration due to loss of GI secretions

Loss of hydrogen ions leads metabolic

alkalosis Prolonged vomiting leads to malnutrition

Loss of chloride ions ( hypochloremia)

motility 1

Documents