The digestive system is the parts of the body that digest food; it is also called the gastrointestinal system. It breaks down food into simple chemicals which can be absorbed into the blood stream. From the blood stream, nutrients go first to the liver, which is a kind of chemical factory for the body. The liver adjusts the nutrients so that the mix is what the body needs. The digestive system consists of gastric acid (hydrochloric acid, potassium chloride, and sodium chloride), which is very reactive and has a pH level of 1.5 to 3.5. The stomach has a protective layer called the mucus.