It consists of just a few kinds of atoms: carbon, hydrogen, oxygen, nitrogen, and phosphorus. Combinations of these atoms form the sugar-phosphate backbone of the DNA -- the sides of the ladder, in other words. Other combinations of the atoms form the four bases: thymine (T), adenine (A), cytosine (C), and guanine (G).
The digestive tract is also called the gastrointestinal (GI) tract or the alimentary canal. It is a continuous tube running from the mouth to the anus.
