Why do you suppose many different structures are needed by the digestive system

 The food that the system processes is made of different things (fats, carbs ,proteins, minerals, fiber, etc.) and it is in different forms (solid, liquid, mush, etc.) naturally you need different tools to process different materials.

Answer in 2009 barack obama signed into law the family smoking prevention and tobacco control act, the new law (h.r.   1256) represents the most sweeping action taken to date to reduce what remains the leading preventable cause of death in the united states;