Chapter 2: The Human Stomach and Gastric Digestion

Gastric digestion is a crucial process in the gastrointestinal tract, where food particles are broken down through mechanical forces, enzymes, and chemical changes. The stomach plays four significant roles in food digestion: temporary storage, mixing with gastric secretions, particle size reduction, and emptying the chyme into the duodenum. The stomach acts as a food storage vessel, allowing food particles to be mechanically disintegrated and chemically digested by gastric secretions and acids and enzymes. The peristaltic movement of the stomach walls generates forces and fluid motions, allowing food and chyme to be broken down and pushed towards the pylorus and small intestine. The duration of gastric digestion and the gastric emptying time vary depending on the food properties, such as structure, viscosity, energy density, and composition. The stomach also plays a prominent role in the nutrient release and absorption mechanisms in the small intestine through chyme formation and regulating gastric emptying rates. The stomach performs various engineering unit operations during the gastric digestion process, including storage, grinding, diffusion, mixing, pumping, and sieving. Further, the functional anatomy of the stomach, the gastrointestinal environment and secretions, physiological processes related to the stomach, such as gastric motility, mixing, and emptying, and also different factors that impact gastric digestion, are all thoroughly covered in this chapter.