How the Stomach Mixes Food: Peristalsis, Retroperistalsis & Gastric Secretions

Mechanisms of Gastric Mixing

The stomach uses coordinated muscular contractions and chemical secretions to turn food into chyme.

1. Peristalsis

Involuntary wave-like contractions from the fundus toward the antrum mix and propel contents.

2. Retroperistalsis

Reverse waves move material from antrum back to fundus, allowing further mixing with gastric juices.

3. Three Muscle Layers

Longitudinal, circular, and oblique smooth muscle layers create churning movements that mechanically break down food.

4. Antral Grinding

Thicker antral walls generate strong contractions that grind large particles into smaller ones, increasing surface area for digestion.

5. Gastric Juices

• Hydrochloric acid (HCl) – kills microbes, activates pepsin.
• Pepsin – begins protein digestion.
• Mucus – protects the stomach lining.

The combined mechanical and chemical action produces chyme, which passes to the small intestine for further digestion and absorption.