Mechanical Digestion The motility of smooth muscle in gastrointestinal tract grinds food and mixes it with digestive juice to prepare it for chemical digestion and absorption, and then propels the food along the gastrointestinal tract. Chemical Digestion: Nutrients in the food are broken down by the enzymes in digestive juice secreted by the secretory glands.Mechanical Digestion: The motility of smooth muscle in gastrointestinal tract grinds food and mixes it with digestive juice to prepare it for chemical digestion and absorption, and then propels the food along the gastrointestinal tract. Chemical Digestion: Nutrients in the food are broken down by the enzymes in digestive juice secreted by the secretory glands