Gastric motility and emptying !

Mechanism
Exam priority: medium

The stomach stores food, grinds it and hands it to the duodenum in small portions, at the pace the gut can handle.

Updated 2026-11-01

Also called: Gastric emptying, Antral pump

See it in 3D: Stomach · Duodenum · Vagus nerve

What it is

The proximal stomach (fundus and body) acts as a reservoir: it relaxes to receive food without a rise in pressure. The antrum is a pump that mixes and grinds with contractions about 3 times a minute, and the pylorus lets only small particles through. Emptying is controlled mainly by the duodenum: if fat, acid or hyperosmolar fluid arrives, hormones and reflexes brake the stomach.

How it works, step by step

On swallowing, the vagus relaxes the fundus and body before the bolus arrives (receptive relaxation).
Food settles in layers; acid and pepsin start working at the edges.
Peristaltic waves start in the mid-body and grow stronger toward the antrum.
As the wave arrives, the pylorus closes; contents hit it and bounce back (retropulsion), mixing and grinding.
With each wave, a small portion of fluid chyme passes into the duodenum.
Acid, fat and hyperosmolality in the duodenum release CCK and secretin and trigger the enterogastric reflex: the antrum contracts less and pyloric tone rises.
When the duodenum has neutralized and absorbed, the brake releases and the next portion leaves.

Regulation

+Gastric distension and the vagus: Increase the strength of antral contractions
+Motilin (fasting): Triggers the migrating motor complex
−CCK and GIP (fat in the duodenum): Relax the proximal stomach and raise pyloric tone
−Secretin and the enterogastric reflex (acid): Reduce antral contractility
−Sympathetic tone, pain, opioids and hyperglycemia: Delay emptying

Clinical notes

Hypertrophic pyloric stenosis: an infant aged 2–8 weeks with projectile non-bilious vomiting, a palpable 'olive' and hypochloremic, hypokalemic metabolic alkalosis.
Diabetic gastroparesis: vagal neuropathy → early satiety, nausea, vomiting of retained food and erratic glucose.
Dumping syndrome after gastric surgery: a sudden load of hyperosmolar fluid in the jejunum pulls in fluid and causes vasomotor symptoms.
Fasting before anaesthesia rests on emptying: clear liquids leave long before fatty meals.

Test yourself

Think of the answer, then tap the question to see it.

Why does a fatty meal stay longer in the stomach?

Fatty acids in the duodenum release CCK and GIP and trigger inhibitory reflexes: the proximal stomach relaxes, the antrum contracts less and pyloric tone rises.

Which acid–base disturbance is expected in hypertrophic pyloric stenosis, and why?

Hypochloremic, hypokalemic metabolic alkalosis: vomiting loses gastric HCl; hypovolemia activates aldosterone, which increases renal K⁺ and H⁺ loss.

What is retropulsion and what is it for?

The backward jet of contents when the antral wave hits the closed pylorus. It mixes and grinds food down to particles of ≈1–2 mm that can pass into the duodenum.

Why could truncal vagotomy cause early fullness?

It removes vagal receptive relaxation of the proximal stomach; intragastric pressure rises with small volumes and the patient feels full early.

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See it in 3D

The structures of Durgical's 3D anatomy where it happens.

In Pharmacology

Opioids and antagonists

← All of physiology

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: 23.4 The Stomach (OpenStax (Rice University), 2022); Pyloric Stenosis (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 64). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.