A pattern of gas and bloating may be an indication that a tumor is growing, especially if it worsens or is accompanied by bleeding. While the formation of a tumor may not be enough to cause a total obstruction, the increasing pressure placed on the colon walls can cause distress and even cramping in the upper intestinal tract.
The more general term glucose syrup is often used synonymously with corn syrup, since glucose syrup is in the United States most commonly made from corn starch.
Corn starch comes from the starchy part of the corn. You are right that corn contains no syrup directly -- the syrup is made from the starch. In the article How Food Works, you learn about starch. Starch is a long-chain carbohydrate -- a polysaccharide.