Gastric Motility

Dr.Mohammed Sharique Ahmed Quadri Assistant Professor Physiology

Almaarefa College

بسم الله الرحمن الرحيم

Objectives

• Describe the functional anatomy of stomach. • Outlines the basic functions of stomach.• Relate the four aspects of gastric motility with

its functions.• Outline the factors affecting gastric motility

and emptying • Apply the physiological concept of gastric

motility and explain process of vomiting.

Stomach

• J-shaped sac-like chamber lying between esophagus and small intestine

• Divided into three sections– Fundus– Body – Antrum The smooth muscle layer in fundus and body are thin, but smooth muscle layer is thick in the antrum.

Stomach

Pyloric sphincterServes as barrier between stomach and upper part of small intestine

Stomach • Three main functions–Store ingested food (4-5 hrs ) until it

can be emptied into small intestine

–Secretes hydrochloric acid (HCl) and enzymes that begin protein digestion

–Mixing movements convert pulverized food to chyme

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STOMACH

What is Chyme?• When ingested food is mixed with gastric

secretions by mixing movements of stomach, a thick liquid mixture known as ‘Chyme’ is produced.

• Chyme is emptied into the duodenum.

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STOMACH

• We will study four basic Digestive Processes in the stomach. These are:

1. Motility 2. Secretion 3. Digestion 4. Absorption

Gastric Motility• Four aspects– Filling• Involves receptive relaxation

– Storage• Takes place in body of stomach

–Mixing• Takes place in antrum of stomach

– Emptying • Largely controlled by factors in

duodenum

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STOMACH

Gastric Filling

• Stomach when empty has volume of 50ml, but it can expand to the capacity of 1 liter [1000ml] during meal [20 fold change in volume].

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Filling/receptive relaxationHOW VOLUME INCREASES?• Because there are folds of mucus membrane in

the stomach they flattens as stomach relaxes when food is taken. It is called ‘Receptive Relaxation’.

• Receptors present in pharynx and lower Esophagus cause receptive relaxation of proximal stomach even before food enters the stomach. This facilitates accommodation of large volumes of food without significant rise of pressure.

• This is mediated by the Vagus nerve.

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Filling/receptive relaxation

• Because of this stomach can accommodate extra volume of food with little rise in pressure

• If more than 1 liter is taken, intra-gastric pressure increases and person experiences discomfort.

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STOMACH ( Motility ) storage :

• The pace-maker cell [interstitial cells of Cajal] are located in the upper fundus region, they generate slow wave at the rate of 3 per min.

• The slow wave or BER [Basic Electrical Rhythm] occur continuously and may or may not generate the contraction of stomach smooth muscle.

• If slow wave reach threshold level then action potential occurs and initiate peristaltic waves.

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STOMACH (Motility)

• Once peristaltic wave occur, it spreads from the fundus, body to antrum and pyloric sphincter.

• Peristaltic wave is weak at fundus and body [as muscle layer is thin] hence food is stored in body of stomach .

• In antrum, peristaltic wave is stronger and more vigorous [as muscle is thick].

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iii. GASTRIC MIXING In Stomach, where mixing of food occurs?• Mainly in the Antrum. Why?• Because muscle in the fundus and body is thin and

mixing movements are feeble and food is stored there.

• When food comes to Antrum, mixing takes place as muscle is thick, therefore, peristaltic waves are strong.

• Fundus usually does not store food but contains gas.

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iii.GASTRIC MIXING

• As food is mixed in antrum, Chyme is produced.• With each peristaltic wave, Chyme is propelled

through pyloric sphincter.• Pyloric Sphincter is normally closed, only water

or fluid can pass.• Antrum can hold 30ml of Chyme and only about

3-5ml of Chyme is pushed into the duodenum with each peristaltic wave.

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iv. GASTRIC EMPTYING

How Gastric Emptying is controlled?• By factors – in the stomach and – in the duodenum.

Factors in stomach affecting gastric emptying

• Amount of chyme in stomach

• Degree of fluidity of chime

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iv. GASTRIC EMPTYING Factors in the stomach: 1. Amount of Chyme in the stomach – if

increased Chyme, increased emptying due to distention .

Stomach distension – causes increased motility -by Direct effect on stretch on the smooth muscle. By stimulation of intrinsic nerve plexus & vagus

nerve Gastrin – released by antral mucosa in response

to stomach stretch and digestive products of meat

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iv. GASTRIC EMPTYING Factors in the stomach: 2. Degree of fluidity of chyme:Increase fluidity allows more rapid

emptying

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iv. GASTRIC EMPTYING Factors in the duodenum• Factors in the duodenum are more important. Duodenum

can delay gastric emptying by decreasing peristaltic activity in the stomach.

• Duodenal factors ( when duodenum has) -- Fat -- Acid -- Hypertonicity -- DistensionThese stimuli in stimulates duodenal receptors, triggering

either neural or hormonal responses that reduces gastric emptying

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iv. GASTRIC EMPTYING

• Duodenal Factors• Duodenal factors work through Neural or

Hormonal response that decreases gastric peristaltic activity in the antrum.

• Neural response is mediated through intrinsic plexus [short reflex] and Autonomic nerves [long reflex].

• These are collectively called ENTROGASTRIC reflex.

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iv. GASTRIC EMPTYING

• Duodenal Factors• Hormonal factors • Hormones released from small intestinal mucosa

are collectively called ‘ENTROGASTRONES’.• Most important Entrogastrone are:• Secretin (produced by endocrine S cells in

Duodenum and Jejunal mucosa)• Cholecystokinin [CCK] produced by I cells in

Duodenum and Jejunal mucosa in response to fat in duodenum

Gastric Emptying• Factors in duodenum– Fat• Fat digestion and absorption takes place

only within lumen of small intestine•When fat is already in duodenum, further

gastric emptying of additional fatty stomach contents is prevented

–Acid• Un-neutralized acid in duodenum inhibits

further emptying of acidic gastric contents until neutralization can be accomplished by pancreatic juice.

Gastric Emptying• Factors in duodenum–Hypertonicity• Gastric emptying is reflexly inhibited

when osmolarity of duodenal contents starts to rise

–Distension• Too much chyme in duodenum inhibits

emptying of even more gastric contents

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GASTRIC MOTILITY

• Factors outside GIT affecting Gastric Motility • -- Sadness and fear – causes decreased

motility. • -- Anger and aggression – leads to

increased motility. • -- Pain – Causes decreased motility

(increased sympathetic activity )

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VOMITING

• It is a protective reflex• It is forceful expulsion of gastric contents

through mouth.• Major force of expulsion comes from

contraction of diaphragm and abdominal muscles.

• There is vomiting center in Medulla, it co-ordinates the act of vomiting.

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VOMITING

• Contracting diaphragm descends downwards on the stomach.

• At the same time, abdominal muscles compress the abdominal cavity and increase the intra-abdominal pressure.

• Stomach is squeezed between the diaphragm above and compressed abdominal cavity below.

• The gastric contents are forced upwards through relaxed sphincter and esophagus, out through the mouth.

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CAUSES OF VOMITING

• Touching the back of throat e.g. seeing the throat using the tongue depressor.

• Distension of stomach.• Increased intracranial pressure e.g. head injury

causing intra cerebral hemorrhage.• Motion sickness.• Drugs.• Renal Failure.• Psychogenic e.g. emotional factors

Vomiting

• Though protective excessive vomiting causes dehydration and acid base imbalance.

• Emetic – substance that induces vomiting

• Antiemetic – substance that inhibits vomiting.

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References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition