Gastric Motility Dr Mohammed Sharique Ahmed Quadri Assistant

ﺑﺴﻢ ﺍﻟﻠﻪ ﺍﻟﺮﺣﻤﻦ ﺍﻟﺮﺣﻴﻢ 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 Ø 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. 6

STOMACH • We will study four basic Digestive Processes in the stomach. These are: 1. Motility 2. Secretion 3. Digestion 4. Absorption 7

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 50 ml, but it can expand to the capacity of 1 liter [1000 ml] during meal [20 fold change in volume]. 9

Filling/receptive relaxation Ø 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. 10

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. 11

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. 12

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]. 13

iii. GASTRIC MIXING Ø 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. 14

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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 30 ml of Chyme and only about 3 -5 ml of Chyme is pushed into the duodenum with each peristaltic wave. 16

iv. GASTRIC EMPTYING ØHow Gastric Emptying is controlled? • By factors – in the stomach and – in the duodenum. 17

Factors in stomach affecting gastric emptying • Amount of chyme in stomach • Degree of fluidity of chime

iv. GASTRIC EMPTYING Ø 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 19

iv. GASTRIC EMPTYING ØFactors in the stomach: 2. Degree of fluidity of chyme: Increase fluidity allows more rapid emptying 20

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 21

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. 22

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 23

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 ) 27

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. 28

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. 29

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 30

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, 11 th edition • Text book of physiology by Linda. s contanzo, third edition 32