the average healthy human adult produces up to one and a half liters of saliva everyday saliva is produced in the mouth where chemical and mechanical digestion begin let's learn more about chemical and mechanical digestion digestion is the process of turning food into its component chemicals once food is broken down into its essential building blocks animals can absorb the calories nutrients vitamins and minerals that allow the body to function grow and repair itself let's take a close look at human digestion the first step in digestion is ingestion of food into the mouth inside the mouth food is chewed by the teeth this begins mechanical digestion this process is the physical breakdown of large pieces of food into smaller pieces after swallowing muscular action of the stomach and intestines continues mechanical digestion during mechanical digestion food also undergoes chemical digestion various chemicals and enzymes break down complex molecules into smaller simpler component molecules that can be absorbed into the bloodstream chemical digestion begins in the mouth as food is chewed salivary glands secrete amylase which converts starch into maltose a disaccharide enzymes and hydrochloric acid in the stomach continue chemical digestion but chemical digestion mostly takes place in the small intestine this begins in the duodenum the first section of the small intestine the pancreas secretes pancreatic juice into the duodenum this strong digestive cocktail converts lipids carbohydrates proteins and nucleic acids into smaller chemical compounds pancreatic juice is alkaline which neutralizes the strong stomach acids by the time food is left the duodenum it has been reduced to its building blocks the small intestine breaks down maltose into glucose completing the chemical breakdown of carbohydrates nutrients and minerals are absorbed through the walls of the small intestine the small intestine is lined with finger-like projections called villi each villus is connected to blood vessels that transport nutrients away undigested food is processed in the large intestine to be ejected as waste via the rectum the dual processes of mechanical and chemical digestion ensure the efficient breakdown in absorption of food the components of food are reduced to their molecular States to enable absorption into the bloodstream