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Theme 1: The Alimentary System > Motility of GI tract > Flashcards

Motility of GI tract Flashcards

1
Q

Gastrointestinal tract

A 
Mouth
Oesophagus
Stomach
Small intestine
Large intestine
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2
Q

Accessory glands

A

Salivary glands
Liver
Gallbladder
Pancreas

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3
Q

Sphincters

A

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

Hold luminal content adequately before emptying to next segment

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4
Q

Dysregulation of sphincters

A

Results in GI motility disorders

  • achalasia
  • gastroparesis
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5
Q

Mucosa layers

A

Epithelial layer

Lamina proporia

Muscularis mucosa

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6
Q

Epithelial layer

A

Exocrine cells and endocrine cells

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7
Q

Lamina propria

A

Small blood vessels

Nerve fibres

Lymphatic cells/ tissue (GALT)

Loose connective tissue

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8
Q

Muscularis mucosa

A

Think layers smooth muscle

Responsible for controlling mucosal blood flow and GI secretion

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9
Q

Submucosa

A

Loos CT, large BVs, lymphatic vessels

Glands in some GI regions

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

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10
Q

Muscularis externa

A

Circular muscle

Myenteric nerve plexus

Longitudinal muscle

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11
Q

Myenteric nerve plexus

A

Auerbach’s

Lies between muscle layers and regulates motility

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12
Q

Serosa

A

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

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13
Q

GI innervation

A

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
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14
Q

Extrinsic innervation

A

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
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15
Q

Intrinsic innervation

A

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
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16
Q

Hirschsprung’s disease

A

Congenital absence of myenteric plexus in portion of distal colon

Lacks peristalsis and undergoes continuous spasms

Leads to functional obstruction and severe constipation

17
Q

Smooth muscle in motility

A

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

18
Q

Regulation of smooth muscle contraction

A

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

Excitatory transmitters depolarise membrane potential

Inhibitory transmitters hyperpolarise membrane potential

19
Q

Types of gastrointestinal movement

A

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
20
Q

Migrating motor complex

A

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

21
Q

Paralytic ileus

A

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

22
Q

Swallowing- deglutition

A

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

23
Q

Oesophagus

A

~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
24
Q

Achalasia

A

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

25
Q

GORD

A

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

26
Q

3 functions of the stomach

A
  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
27
Q

Receptive relaxation

A

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

28
Q

Mixing

A

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

29
Q

Emptying

A

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

30
Q

Control of stomach emptying

A

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

31
Q

Dumping syndrome

A

Rapid emptying of gastric contents into small intestine

Nausea, pallor, sweating, vertigo, fainting after meal

32
Q

Gastroparesis

A

Impaired of absent ability of stomach to empty

Occasionally in severely diabetic patients

Early satiety, abnormal bloating, nausea

33
Q

Motility along small intestine

A

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

34
Q

Small intestine motility dysfuntions

A

Impaired small intestine peristalsis can lead to abnormally high bacteria

Lead to diarrhoea/ steatorrhoea

Intestinal blind loop syndrome

35
Q

Motility in large intestine

A

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

36
Q

Rectum and defecation

A

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

Theme 1: The Alimentary System (16 decks)

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