Motility of GI tract

Question 1

Gastrointestinal tract

Answer 1

Mouth
Oesophagus
Stomach
Small intestine
Large intestine

Question 2

Accessory glands

Answer 2

Salivary glands
Liver
Gallbladder
Pancreas

Question 3

Sphincters

Answer 3

Made up of smooth muscle and act as ‘valve of reservoir’

Hold luminal content adequately before emptying to next segment

Question 4

Dysregulation of sphincters

Answer 4

Results in GI motility disorders

• achalasia
• gastroparesis

Question 5

Mucosa layers

Answer 5

Epithelial layer

Lamina proporia

Muscularis mucosa

Question 6

Epithelial layer

Answer 6

Exocrine cells and endocrine cells

Question 7

Lamina propria

Answer 7

Small blood vessels

Nerve fibres

Lymphatic cells/ tissue (GALT)

Loose connective tissue

Question 8

Muscularis mucosa

Answer 8

Think layers smooth muscle

Responsible for controlling mucosal blood flow and GI secretion

Question 9

Submucosa

Answer 9

Loos CT, large BVs, lymphatic vessels

Glands in some GI regions

Submucosal nerve plexus (Meissners plexus)- regulates blood flow and secretion

Question 10

Muscularis externa

Answer 10

Circular muscle

Myenteric nerve plexus

Longitudinal muscle

Question 11

Myenteric nerve plexus

Answer 11

Auerbach’s

Lies between muscle layers and regulates motility

Question 12

Serosa

Answer 12

CT connects to abdominal wall

Supports GI tract in the abdominal cavity

Blood vessels, extrinsic nerves and ducts of large accessory exocrine glands enter through

Question 13

GI innervation

Answer 13

Intrinsic pathway

• enteric nervous system
• functionally organised by submucosal and myenteric plexus
• myenteric involved in control of gut motility
• submucosal coordinates intestinal absorption and secretion

Extrinsic pathway

• the gut brain axis
• ENS linked to CNS via sensory and motor nerve
• parasympathetic and sympathetic nervous system

Question 14

Extrinsic innervation

Answer 14

Parasympathetic

• preganglionic vagus nerve innervates oesophagus, stomach, small intestine, liver, pancreas, caecum, appendix, ascending colon, transverse colon
• pelvic nerve innervates remainder of colon via hypogastric plexus
• stimulates motility and secretion

Sympathetic

• preganglionic fibres from T8-L2
• postganglionic cell bodies in celiac, IM and SM ganglia
• inhibits gut motility and secretion
• constricts sphincters

Question 15

Intrinsic innervation

Answer 15

Myenteric plexus

• between circular and longitudinal muscle layers
• thin layer of ganglia, ganglion cells and inter-ganglionic nerve tracts
• innervate longitudinal and outer lamella of circular
• control of gut motility

Submucosal plexus

• between submucosal layer and circular layer
• functionally distinct from myenteric plexus
• project mainly into inner lamella of circular
• coordinates intestinal absorption and secretion

Question 16

Hirschsprung’s disease

Answer 16

Congenital absence of myenteric plexus in portion of distal colon

Lacks peristalsis and undergoes continuous spasms

Leads to functional obstruction and severe constipation

Question 17

Smooth muscle in motility

Answer 17

Act as functional syncytium

Pacemaker activity- slow waves- BER

Spike potentials of BER depolarises membrane to threshold (caused by opening of Ca2+ channels)

Ca2+ in spike potential triggers muscle contraction

Question 18

Regulation of smooth muscle contraction

Answer 18

Greater the number of spikes per BER the greater the degree of muscular contraction

Excitatory transmitters depolarise membrane potential

Inhibitory transmitters hyperpolarise membrane potential

Question 19

Types of gastrointestinal movement

Answer 19

Segmentation

• mainly small intestine for mixing food with enzymes
• closely spaced contractions of circular smooth followed by relaxation

Tonic contraction

• sphincters
• separation

Peristalsis

• longitudinal contracts first then circular
• leads to progressive wave
• distension of gut by food triggers peristalsis

Question 20

Migrating motor complex

Answer 20

Pattern of motility every 90 minutes between meals

Strong propulsive contractions down distal stomach and small intestine

Sweep indigestible materials

Does not require external innervation

Question 21

Paralytic ileus

Answer 21

Temporary cessation of gut motility most commonly caused by abdominal surgery

Also caused by infection or inflammation of abdominal cavity, electrolyte abnormality and drug ingestion

Nausea, vomiting, abdominal distention, absent bowel sounds

Question 22

Swallowing- deglutition

Answer 22

Bolus of food formed in mouth by mastication then propelled to oropharynx as tongue moves up and back against hard palate (V)

Bolus stimulates mechanoreceptors in parynx

Efferent impulses from vagus to pharynx, oesophagus and palate for muscle contraction

Soft palate elevates, superior constrictor of pharynx contacts to close nasopharynx

Larynx rises so epiglottis covers trachea

Peristalsis initiated in pharynx continues down oesophagus

Question 23

Oesophagus

Answer 23

~25cm

Upper 1/3 skeletal striated muscle, lower 2/3 smooth

On swallowing

• UOS briefly relaxes, allows food to pass to oesophagus
• contractile wave sweeps down oesophagus
• LOS and proximal stomach relax to allow bolus to enter

Question 24

Achalasia

Answer 24

Dysphagia results from failure of LOS to relax, causing functional obstruction

Loss of peristalsis of oesophageal body

Lose ganglionic cells of myenteric plexus or natural defects in vagal dorsal nucleus of brainstem

Question 25

GORD

Answer 25

LOS is incompetent, allows flow of gastric juices and content back into oesophagus Gastric juices are corrosive so distal oesophagus becomes inflamed and sometime ulcerated

Question 26

3 functions of the stomach

Answer 26

1. Storage- ingest food faster than can be digested, aided by receptive relaxation 2. Physical and chemical disruption- mixing 3. Deliver resultant chyme to intestine at optimal rate- gastric emptying

Question 27

Receptive relaxation

Answer 27

Increases in stomach pressure triggers dumping and reflux Relaxation of muscle- increase in fibre length without change in tone Increase in size without increase in intragastric pressure Receptive relaxation mediated by vagus as part of end of swallowing reflex Pressure sensors maintain pressure at abdominal levels Occurs in proximal unit

Question 28

Mixing

Answer 28

Peristalsis through strong coordinated contraction of three muscle layers in distal Cells in longitudinal act as pacemakers Activity originates mid stomach Spreads distally and force and speed increases Little chyme forced to duodenum, most content returns to distal regions

Question 29

Emptying

Answer 29

Terminal part- pyloric antrum markedly thickened muscle layer Pyloric sphincter controls exit Increase of chyme induces antral contractions and opening of sphincter as peristaltic wave approaches Small amounts of cyme enters duodenum, sphincter contracts Liquids leave first

Question 30

Control of stomach emptying

Answer 30

Small intestine has limited capacity so only accept small amounts of chyme Gastric contents empties at rate proportional to volume, pH, physical and chemical natire - volume in stomach promotes emptying - more isotonic, empties more rapidly Enterogastric reflex stimulates pyloric contraction to prevent emptying and prevent overfilling over small intestine

Question 31

Dumping syndrome

Answer 31

Rapid emptying of gastric contents into small intestine Nausea, pallor, sweating, vertigo, fainting after meal

Question 32

Gastroparesis

Answer 32

Impaired of absent ability of stomach to empty Occasionally in severely diabetic patients Early satiety, abnormal bloating, nausea

Question 33

Motility along small intestine

Answer 33

Mixing: multiple short contractions, frequency varies Peristalsis: short range contractions Stimulated by extrinsic and intrinsic factors Villus movements mix and drain lymphatics of fat absorption

Question 34

Small intestine motility dysfuntions

Answer 34

Impaired small intestine peristalsis can lead to abnormally high bacteria Lead to diarrhoea/ steatorrhoea Intestinal blind loop syndrome

Question 35

Motility in large intestine

Answer 35

Slow, irregular movements increase contact with absorbing surface lacks longitudinal muscle, instead has 3 thick bands for accordion like movement Contractions of circular muscle divide colon to haustrations Mixing movement Propulsive movement

Question 36

Rectum and defecation

Answer 36

Mass movement propels faeces into rectum and distends stretch receptors to provoke defecation reflex Internal anal sphincter- involuntary External anal sphincter- voluntary Afferent stimulation leads to parasympathetic signal to relax internal sphinter