2017B Question 10

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

Examiner Report

29.2% of candidates achieved a pass in this question The main points expected are best organised into local, neural and humoral control of gastric emptying of chyme into the duodenum.Candidates with a clear understanding of the reason for the coordinated emptying scored better in this question, which had asked for a description of physiological processes. However, a number of candidates were also awarded marks for pathophysiological and pharmacological factors; if there was prior demonstration of knowledge of normal physiology. Only a few candidates correctly pointed out that pregnancy does not delay gastric emptying; but the stress of labour does.

Common mistakes were

  • Answering in tabular format, which listed factors that increase or decrease gastric emptying without further discussion.
  • Answering in a clinical approach (patient, surgical and anaesthetic factors), which led to omission of essential physiological facts.
  • Confusion about the hormones that are involved and their exact effects on gastric emptying.
  • Regurgitation of fasting guidelines for patients without explaining the physiological basis for these guidelines.
  • Detailed discussion of gastric acid production or function of the lower oesophageal sphincter, which is not within the scope of this question.

Model Answer


  • Introduction
  • Physicochemical
  • Neural: Extrinsic and intrinsic
  • Hormonal factors


Factor Details

- 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)


Factor Details

- Starch meal: ~2-3 hours

- Proteinaceous meal: ~3-4 hours

- Fatty meal: 6 hours


- Liquid faster than solid


- ↑ Osmolality → ↓ GER

Neural Factors

Intrinsic Factor Stimulus Effect

Meissner’s plexus


- ?Distension

- ?CHO, protein, 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, protein, high osmo

- ↓ AC

Extrinsic Factor Stimulus Effect
PSNS: CNX via coeliac and superior mesenteric plexuses

- ?Distension

- ?CHO, protein, 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

Hormonal Factors

Stimulate Antral Contraction Source Release stimulus

- Gastric G cells

- Duodenal protein

- Gastric distension


- Duodenal M cells

- Duodenal fat, acid


- Islet β cells

- Hyperglycaemia


- Duodenal wall?

Inhibit antral contraction Source Release stimulus

- Duodenal I cells

- Duodenal fat, protein, acid

Secretin (conflict)

- Duodenal S cell

- Duodenal fat, acid


- Duodenal K cells

- Duodenal fat, protein, CHO

Last updated 2021-08-23

results matching ""

    No results matching ""