git phsyiology part i by dr a.k.gupta

8/14/2019 GIT PHSYIOLOGY Part I BY DR A.K.GUPTA

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Mastication (Chewing)Chewing is the first mechanical process in the GI tract in whichfood is broken down into small particles and a soft bolus is formed.

Importance of Chewing

3. Food is broken into small particles required for enzymeactions.

4. Mixing with saliva so that bolus can be swallowedeasily

6. Grinding the food to a very fine particles preventsinjury to the GIT

Muscles of Mastication:

1.Masseter 2. Temporal 3. Pterygoids 4. Buccinator.

Movements associated with Mastication:

11.Opening & closure of mouth


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Control Of mastication

.1. The centre for mastication is located in medulla & cerebralcortex.

2. The muscles of mastication are suplied by mandibular division of

V cranial nerve.

(V cranialNerve)


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Swelling can be divided into

(2)Oral Stage : a voluntary stage, in whichfood enetrs pharynx frommouth.

(3)Pharyngeal stage- an involuntary stage

in which food is enters esopahgus fromthe pharynx.

(4)Esophageal stage-involuntary phase inwhich food enters stomach from theesophagus.


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1. Oral Stage of

1. Voluntary Stage in which after the Food isrolled into a bolus by chewing followingactions occur:

2. The bolus is placed on poster-odorsal part of

tongue3. The anterior part of tongue is retracted &

depressed4. The posterior part of tongue is elevated and

pressed against hard palate. This pushes the

bolus backward into pharynx.


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2. Pharyngeal Stage of Swallowing

It is an Involuntary stage

The pharynx is a common passage for food and air. It has twoexits one into esophagus for food the other into larynx for air.

The Larynx lies anterior to esophagus opening. Esophagusopening lies posterior to larynx opening. Further, pharynx is alsoconnected to naso-pharynx behind nose . So food in pharynx cango to esopahagus or larynx or nose or back to mouth.

It is ensured that the food enters only esophagus as under:

d. Return of food back into mouth is prevented by tonguebeing pressed against the palate creating high pressure in oralcavity

e. Entry of food into naso-phayrynx is prevented by elevationof soft palate & uvula.

f. Entry of food intolLungs through larynx is prevented by

7 Vocal cords of two side come very near each

8 Larynx move forward & upward

9 Epiglottis cover the larynx opening glotiis.

10 Temporary arrest of breathing during this stage of deglutition


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d. Entry of food into esophagus: Now the other 3passages as mentioned above are closed so foodcan enter only esopahagus by following

mechanism:2 When larynx moves upward it opens the esophagus

opening wider.

3 The upper 3-4 cm of esophagus called UES (Upper

Esophageal Sphincter) relaxes4 Contraction of pharyngeal muscles forces food into

esopahgus.


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3. Esophageal Stage of Swallowing. It is also involuntary.When bolus reaches the esophagus peristaltic movementsstarts in esophagus to propel food down into stomach.

Two types of peristaltic movements:primary peristalsisandsecondary peristalsis.

Primary peristalsisis continuation of the peristaltic wave thatbegins in the pharynx & passes all the way from the pharynxto the stomach in about 8 to 10 seconds.

Secondary Peristalsis : It remove any retained food particlesfrom esophagus if primary peristalsis fails to remove them andsend to stomach.

Role of LES (Lower Esophageal Sphincter)

6. When a peristaltic wave passes down the esophagus, thereis "receptive relaxation" of the lower esophageal sphincterahead of the peristaltic wave, which allows easy propulsionof the swallowed food into the stomach.

7. After entry of food into stomach, LES contracts to not allow

reflux of acid of stomach into esophagus. However, . If the


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Deglutition Reflex

Ist stage of deglutition is Voluntary while 2nd & 3rd Stagesof Deglutitin are Involuntary and through deglutition

reflex mechanism.Stimulus: The sensory receptors in oro-phayrynx speciallyarea in a ring around the pharyngeal opening, withgreatest sensitivity on the tonsillar pillars getsstimuted when food reaches here.

Afferent Fibres: impulses from pharyngeal receptors passthrough glasso-pharyngeal nerve (IX cranial nerve) todeglutititon or swallowing centre in medulla (see nxt slidefor photo).

Deglutition Centre: it is located in floor of 4th

Ventricle inMedulla oblongata of brain.

Efferent Fibres: Impulses from deglutition centre travelthrough glasso-pharyngeal nerve (IX cranial nerve) & vagusnerve (X cranial nerve) & reach soft palate, palate, pharynx,

& esophagus.


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APPLIED PHYSIOLOGY

1. Dysphagia: it is difficulty in swallowing.

Causes:c. Mechanical obstruction in esophagus

tumor, stricture, diverticula

d. Decresaed movements of esophagus egin parkinsonism a neurological disorder.

e. Muscle dosrders with theresult dificult

swallowing during oral & esophgealstages.


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APPLIED PHYSIOLOGY

2. Achalasia: When Lower esophageal

sphincter fails to relax during swallowingthe food accumulates in esophagus causingits distention and symptoms as under:

b. Dysphagia

c. Chest pain

d. Weight loss

e. Cough


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APPLIED PHYSIOLOGY

3. GERD (gastro esophageal reflux

disease)Due to weakness or failure of LowerEsophageal Sphincter to constrict causing

reflux of acid contents of stomach intolower end of esophagus causing refluxesophagitis with symptoms:

c. Heart burnd. Esophagitis

e. Dysphagia


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MOVEMENTS OF STOMACH

1. HUNGER CONTRACTIONS

2. RECEPTIVE RELAXATION3. Peristalsis of Stomach: FILLING &

EMPTYING

1. HUNGER CONTRACTIONS:

When the person is empty stomach hungercontractions occurs. They are peristaltic waves

superimposed upon normal smooth musclecontractions.

The peristaltic waves of normal stomach whenfood is there occur in body & pyloric part of


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Type of HUNGER CONTRACTIONS

Type I:

They are the first contractions in empty stomach when stomach tone islow.

Their duration is 20 seconds & occur every 3-4 seconds.

they produce a pressure of 5 cm of water &

Stomach tone is normal in between the contractions.Type II:

They appear when tone of stomach is stronger and if the food intake ispostpones even on start of Type I Hunger Contractions.

Their duration of each contraction is 20 seconds like in type I but there is

no pause between the contractions so thePressure produced in stomach is 10-15 cm of water.

Type III:

Occur when food is not taken despite type II contractions,

It is incomplete tetanus and tone of stomach muscle increases muchmore.


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APPLIED PHYSIOLOGY

2. RECEPTIVE RELAXATION OFSTOMACH:

Relaxation of upper part of stomachwhen bolus of food enters thestomach from esophagus is calledRECEPTIVE RELAXATION, It occurs infundus, and upper part of body ofstomach to receive & accommodate

food without increase in pressure ofstomach so no discomfort to person.


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Peristalsis of Stomach

1. When food enters stomach-smoothmuscle of stomach start contracting @

3/min. The contractions start in lower partof body of stomach & pas to the pyloricsphincter. The contractions move towards

pyloric sphincter and takes 1 min to reachat pyloric sphincter from point of origin inbody of stomach. They are calleddigestive peristalsis because with tightpyloric end food is crushed by them instomach and grinded for better action ofjuices & enzymes.

git phsyiology part i by dr a.k.gupta

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