Download Stomach

Gastric Motility
Dr.Mohammed Sharique Ahmed Quadri
Assistant Professor Physiology
Almaarefa College
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 sphincter
Serves 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
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
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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
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 relaxation
 HOW 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.
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Factors in stomach affecting gastric
emptying
• Amount of chyme in stomach
• Degree of fluidity of chime
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
-- Distension
These 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
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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 coordinates 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 intraabdominal 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
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Vomiting
• Though protective excessive vomiting causes
dehydration and acid base imbalance.
• Emetic – substance that induces vomiting
• Antiemetic – substance that inhibits vomiting.
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
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