A catalyst is a chemical involved in, but not changed by, a chemical reaction. Many enzymes function by lowering the activation energy of reactions. By bringing the reactants closer together, chemical bonds may be weakened and reactions will proceed faster than without the catalyst.
The human digestive system is made of gastroenteritis and organs such as saliva, tongue, and glands, etc. The digestion involves the breakdown of food substances into smaller components.
This begins in three phases. Chewing leads to the breakdown of food, saliva contains enzymes and the stomach consists of gastric glands.