"polysaccharides" are chains longer than ten sugars and are familiar to most people as simply "starch".
The human small intestine can only absorb simple sugars like glucose. Every other kind of carbohydrate from table sugar to potato starch must first be digested by enzymes that eventually break the carbohydrate down entirely into simple sugars.
Carbohydrate metabolism, like nearly all metabolism, is extremely complex and far beyond the scope of this website. Still, several points should be stressed.
-Carbohydrate is the only macronutrient that is not essential for human life. In the total absence of dietary carbohydrate, the body produces ketone bodies to keep the brain alive and manages to actually make glucose from certain amino acids and from glycerol that is liberated from triglycerides. This process of glucose synthesis is called "gluconeogenesis" and is discussed elsewhere.
-Carbohydrate that circulates in the blood is always in the form of a monosaccharide and by far the most prevalent of these monosaccharides is glucose or "blood sugar".
-Increasing levels of blood glucose trigger the pancreas in healthy people to secrete the hormone "insulin" which causes muscle and other tissue to absorb glucose from the blood and therebye maintain glucose levels within a limited range.
-The disease of "diabetes mellitus" is named for the fact that it causes people to have sweet tasting urine (this truly was an ancient way of diagnosing the disease and the sweet flavor is due to the presence of large amounts of glucose in the urine caused by extremely high blood glucose levels.
-Diabetes mellitus is the name given to two totally different diseases that happen to both share the feature of very high blood glucose levels.
-Type-1 diabetes is also called "childhood-onset" diabetes, tends to strike children and young adults, tends to develop extremely rapidly(often within weeks) and is usually very serious and hard to control from the outset. Nearly all patients with type 1 diabetes are insulin dependant. Type-1 diabetes is caused by a failure of the pancreas to produce insulin due to the sudden death of all or nearly all of its insulin-producing cells. Most scientists believe that type 1 diabetes is caused by a virus although the causitive agent is not certain.
-Type-2 diabetes is also called "adult-onset" diabetes and tends to develop in adults. Type-2 diabetes usually develops slowly and worsen slowly over years. Type-2 diabetes is caused not by a lack of insulin production from the pancreas, but rather by insulin resistance. Among the strongest risk factors for type-2 diabetes are obesity, metabolic syndrome, family history and early indications of insulin resistance like rising glyco-hemoglobin (HbA1C) levels. Type-2 diabetes presents in varying degrees of severity: some people can control it just by reducing sugar and carbohydrate in their meals, many patients achieve good control through the use of one or a combination of several oral medications while some type-2 diabetics require insulin injection.