For a more technical answer - Sugar ingestion (complex sugar like starch or simple Sugar ingestion (complex sugar like starch or simple sugar like glucose, galactose and fructose) is usually through the oral route, thus digested simple sugars (again, there are 3 kinds of simple sugar as I just listed) enter the blood stream through the blood vessels in your small intestines' microvilli. Sugar can also enter the blood stream through the liver after gluconeogenesis (making of glucose from other sources such as lactic acid, glycerol and glucogenic amino acids) or glycolysis (such as glycogen breakdown in the liver to release glucose). If you have a D5W or TPN (total parenteral nutrition) through an IV (intravenous) line in the hospital, sugar can directly enter your blood stream through the IV line. When some diabetic patients have overdose of insulin or diabetes drugs that lead to transient hypoglycemia and need to restore their blood glucose FAST, a sublingual tablet of glucose (like some candies that give a quick sugar boost) can also enter the blood stream sublingually (under the tongue where there are some blood vessels). If you study pharmacy and learn how drugs can reach the systemic circulation, you will learn there are so many routes that can be used to administer a drug, such as per rectum, per vagina, intranasal, intravenous, oral, sublingual, transdermal, subcutaneous, inhalation, etc like glucose, galactose and fructose) is usually through the oral route, thus digested simple sugars (again, there are 3 kinds of simple sugar as I just listed) enter the blood stream through the blood vessels in your small intestines' microvilli.
