According to HowStuffWorks, glucose enters the bloodstream through the intestinal lining. Only two carbohydrates other than glucose are directly absorbed into the bloodstream by this means: fructose and galactose. These three carbohydrates are known as monosaccharides.
Disaccharides are combinations of two monosaccharides. HowStuffWorks states that enzymes in the digestive tract break disaccharides into their component parts, allowing for the bloodstream to absorb the carbohydrates. The digestive system also breaks down more complex carbohydrates, such as those found in grains and potatoes, into glucose molecules to allow for absorption into the bloodstream. Sugar is the common term that refers to both monosaccharides and disaccharides, while many people know complex carbohydrates as starch.