Gastric motility Flashcards
What is GI motility?
Gastrointestinal motility is the movements of the digestive system and how its contents transit within it.
It involves coordinated contractions and relaxations of the GI tract that moves content from the mouth to the anus.
What are the three patterns of motility?
Peristalsis - 1 direction, transport
Segmentation - back and forth, mixing
Tonic contraction - opening and closing, blocks passage separation
What are the muscles of the GIT?
Smooth muscles are involuntary. 2 layers - inner (circular) and outer (longitudinal).
Skeletal muscles are voluntary. Found in the pharynx, top 1/3 of oesophagus, external anal sphincter.
What is smooth muscle motility?
Phasic
Tonic
What is phasic motility?
Rapid contractions
Peristalsis and segmentation
In the body of the oesophagus, stomach antrum, and small and large intestines.
What is tonic motility?
Sustained contractions
Sphincters and upper stomach
What are enteric sensory neurones?
Intrinsic primary afferent neurons (IPANs).
Distension (Stretch) is detected by mechanoreceptors. Myenteric plexus
Chemoreception - acid and short chain fatty acids can also trigger neurones. Related to submucosa.
What is the enteric nervous system?
Made up of myenteric plexus and submucosal plexus.
What does activation of the myenteric plexus do?
Increases tonic contraction
Increases intensity of rhythmic contractions.
Rate of rhythmic contractions increases velocity of conduction.
What does activation of the submucosal plexus do?
Increases secretory activity
Modulates intestinal absorption.
What is gastric motility for food storage?
This is concerned with the contractions or relaxations of the smooth muscles in the stomach wall.
What does the stomach do when empty?
When the stomach is empty, volume if 50ml.
When a meal is swallowed, smooth muscles in the fundus relax before the food arrives in the stomach - distension.
The stomach increases to 1.5L with little increase in pressure.
How is relaxation of the stomach regulated?
Relaxation and stretch is regulated by receptive relaxation - a Vago-vagal reflex.
If vagal innervation is interrupted then intra-gastric pressure increases.
What is the order of gastric motility?
Propulsion
Grinding
Retropulsion
The processes repeat multiple times until the gastric contents are emptied.
What is sieving function?
Liquids and small particles leaves the stomach more rapidly than large particles.
What is propulsion?
Movement of solid particles towards the antrum is accomplished by the interaction of propulsive gastric contractions and occlusion of the pylorus.
These contractions propel the luminal contents towards the pylorus, which is partially closed by contraction of the pyloric musculature before delivery of the bolus.
What is grinding?
Once a bolus of material is trapped near the antrum it is churned to help reduce the size of the particles.
Only material that contains particles less than 2mm is propelled through the pylorus to the duodenum.
What is retropulsion?
Pylorus checks that the particles of food are less than 2mm.
Most of the gastric contents are returned to the bolus of the stomach for pulverisation and shearing of solid particles, so they are less than 2mm.
What is gastric emptying?
The process where the contents of the stomach are discharged into the duodenum
This is primarily regulated by the autonomic nervous system (Vagus nerve) and gastrointestinal hormones.
What does the pyloric sphincter do in gastric emptying?
The pyloric sphincter allows carefully regulated emptying of gastric contents.
This prevents regurgitation of duodenal contents back into the stomach.
It is innervated by Vagus - relaxation, and sympathetics - constriction.
What is the cephalic phase related to gastric emptying?
Inhibitory - by inhibitory nerve fibres in the vagus nerve.
Results in relaxation of the stomach, enabling it to store large volumes, prevents food emptying.
What is the gastric phase related to gastric emptying?
Excitatory - the stomach empties at a rate proportional to the volume in it.
What is the gastric phase caused by?
Myogenic reflex - stretching smooth muscles causes relfex contraction.
Activation of pressure receptors which send impulses in local nerve plexi and the vagus nerve.
Gastrin released in response to peptides.
What is the intestinal phase in relation to gastric emptying?
Inhibitory - the duodenum adapts the work load as a function of the state of the digestive process.
Mainly controlled by hormonal and paracrine mechanisms, which is activated by duodenal chemoreception.
