Final answer:
The first short portion of the small intestine that comes off the stomach is the duodenum, responsible for the majority of chemical digestion.
Step-by-step explanation:
The first short portion of the small intestine that comes off the stomach is the duodenum. The duodenum is the first part of the small intestine, directly connected to the stomach. It is also the shortest section, measuring about 25 cm (10 in.) in adults, and is primarily responsible for most of the chemical digestion in the gastrointestinal tract. The other sections of the small intestine include the jejunum, the second part where the majority of nutrients are absorbed into the blood, and the ileum, the third and longest part, which absorbs vitamin B12, bile salts, and other remaining nutrients.