Digestion involves breaking organic compounds into simple soluble substances absorbable by tissues. This process involves catalytic reactions between ingested food and enzymes secreted into the intestinal tract Digestion of fatty substances appears to involve the assembly of bile salts, phospholipids, fatty acids, and monoglycerides permeable to intestinal cells. The process described here is typical of all vertebrates except ruminants .
Digestion includes both mechanical and chemical processes.
The mechanical processes include chewing to reduce food to small particles, the churning action of the stomach, and intestinal peristaltic action. T hese forces move the food through the digestive tract and mix it with various secretions. These processes are accomplished by specific enzymes. W hen food is eaten, the six salivary glands produce secretions that are mixed with the food. The saliva breaks down starches into dextrin and maltose, dissolves solid food to make it susceptible to the action of later intestinal secretions, stimulates secretion of digestive enzymes, and lubricates the mouth and oesophagus for the passage of solids.