2017B10 Describe the physiological processes that influence the rate of gastric emptying.

· Intro

· Physicochemical

· Neural: extrinsic and intrinsic

· Hormonal factors

Significance

· Gastric emptying rate (GER) varies to ensure chyme adequately digested

· Full stomach -> ↑↑risk of aspiration under GA

· GER highly variable -> important to assess for pain, opioid use, sepsis

Normal physiology

· Antral waves, 3 per minute

· GER ∝ antral contraction freq and strength (AC) / pyloric resistance (PR)

Substrate

· Starch meal: ~2-3 hours

· Proteinaceous meal: ~3-4 hours

· Fatty meal: 6 hours

Form

· Liquid faster than solid

Concentration

· ↑Osmolality -> ↓GER

Intrinsic:

	Stimulus	Effect
Meissner’s plexus (submucosal)	? Distension ? CHO, prot, fat	Controls local absorption, secretion, contraction
Auerbach’s plexus (between longitudinal and circular muscle layers)	? Distension	Controls local contraction
Myenteric reflex	Distension	Peristalsis (↑AC)
Enterogastric reflex	Duodenal distension, irritation, acid, fat, prot, high osmo	↓AC

Extrinsic:

	Stimulus	Effect
PSNS: CNX via coeliac and superior mesenteric plexuses	? Distension ? CHO, prot, fat	↑Local ACh release ↑AC, ↓PR
SNS: T5-L1 via same plexuses	Exercise, pain, anxiety/stress, Labour (not pregnancy)	↓Local ACh release ↓AC, ↑PR
Vago-vagal excitatory reflex: CNX only	Gastric distension	Receptive relaxation ↑AC

Stimulate antral contraction:

	Source	Release stimulus
Gastrin	Gastric G cells	Duodenal protein Gastric distension
Motilin	Duodenal M cells	Duodenal fat, acid
Insulin	Islet β cells	Hyperglycaemia
Serotonin	Duodenal wall?	?

Inhibit antral contraction: