by PhilipJ on 2 February 2006
Glucose is a major source of energy in your body, but unfortunately, free glucose is relatively rare in our typical diet. Instead, glucose is locked up in many larger forms, including lactose and sucrose, where two small sugars are connected together, and long chains of glucose like starches and glycogen. One of the major jobs of digestion is to break these chains into their individual glucose units, which are then delivered by the blood to hungry cells throughout your body.
Alpha-amylase begins the process of starch digestion. It takes starch chains and breaks them into smaller pieces with two or three glucose units. Two similar types of amylase are made in your body—one is secreted in saliva, where it starts to break down starch grains as you chew, and the other is secreted by the pancreas, where it finishes its job. Then, these little pieces are broken into individual glucose units by a collection of enzymes that are tethered to the walls of the intestine.
High resolution pictures and further info here.