Gastric Motility Flashcards
What is the volume of an empty stomach?
50ml
When eating, how much can the stomach accomodate?
1.5L with little increase in luminal pressure
How does the stomach vol increase with little increase in luminal pressure?
It does this by the smooth muscles in the body and fundus undergo receptive relaxation
What is receptive relaxation mediated by?
Mediated by parasympathetic NS acting on enteric nerve plexus
Where is co ordination for receptive relaxation found?
Afferent Input from stomach via vagus nerve and swallowing centre in brain
What is released by the enteric nerves to mediate relaxation?
Nitric oxide & serotonin
What does acetyl choline do in regards to receptive relaxation?
ACh activates parietal & chief cells and initiates receptive relaxation
What happens in peristalsis?
Peristaltic waves begin in the gastric body
Weak contraction in body (little mixing of luminal contents with acid and pepsin)
More powerful contraction in gastric antrum Pyloric sphincter (ring of smooth muscle &connective tissue between the antrum and duodenum)closes as peristaltic wave reaches it
Little chyme enters duodenum
Antral contents forced back towards body (more mixing=digestion)
What is the frequency of the peristaltic waves determined by?
Pacemaker cells (interstitial cells of cajal) in the muscular propria (longitudinal smooth muscle)
How much chyme enters the duodenum at a time?
What happens to the rest?
Only 3ml
rest is pushed back to stomach
How often do the peristaltic waves take place?
Constant - 3 per min
What do pacemaker cells undergo?
Slow depolarization-repolarisation cycles
Where do the depolarization waves transmit through?
What do these not cause?
Gap junctions to adjacent smooth muscle
Significant contraction in the empty stomach
How does the strength of the peristaltic contraction vary?
Excitatory neurotransmitters & hormones further depolarize membranes
Action potentials are generated when threshold is reached
How can the action potential threshold for muscle contraction be altered?
The interstitial cells of cajal are active all the time, but the action potential threshold can be altered by the enteric NS
Where are strength of contractions increased by? (2)
Gastrin Gastric distension (mediated by mechano receptors)
What are strength of contractions decreased by?
Duodenal distension Increase in duodenal fat Increase in duodenal osmolarity Decrease in duodenal pH Increase in sympathetic NS stimulation Decrease in parasympathetic NS stimulation
Does the stomach or duodenum have a greater capacity?
Capacity of stomach is greater than duodenal capacity
What happens when the duodenum is overfilled by a hypertonic solution?
Causes dumping syndrome
Vomiting, bloating, cramps, diorrhoea, dizziness, fatigue, weakness, sweating
What happens as gastric contents enter duodenum?
Duodenal pH falls
What is gastroparesis?
Delayed gastric emptying
food rots in stomach
What can gastroparesis be caused by?
Idiopathic (unknown cause) Autonomic neuropathies (eg. Diabetes mellitus) Drugs Abdominal surgery Parkinson’s disease Multiple sclerosis Scleroderma Amyloidosis Females
What drugs can cause gastroparesis?
H2 receptor antagonists Proton pump inhibitors Opioid analgesics Beta adrenergic receptor agonists Calcium channel blockers Levodopa
What are the symptoms of delayed gastric emptying?
Nausea Early satiety (feeling full early) Vomiting undigested food Cause matter in stomach to rot and smell-similar to faeces in looks GORD Abdo pain/bloating Anorexia
