The digestive system facilitates the progression of ingested nutrients along the digestive tract, the breakdown of large molecules into smaller building blocks by digestive secretions, and the absorption of these building blocks, water, and electrolytes into the bloodstream.

Digestion begins with the intake of food into the mouth. In the mouth, food is broken into smaller pieces by chewing, mixes with saliva, and then passes into the stomach via the esophagus. The stomach, through its secretions, converts the swallowed food into a semi-liquid state before passing it to the small intestines; it also breaks down proteins into smaller building blocks.

The semi-liquid food that enters the small intestines is digested and absorbed with the help of bile and pancreatic secretions. The large intestines absorb water and electrolytes and serve as a storage site until feces are eliminated.