Physiological importance of monosaccharides (simple carbohydrates)

Hexoses of physiologic importance

  • D-Glucose – is present in fruit juices, obtained by hydrolysis of starch, canesugar, maltose, and lactose. It is the “sugar” of the body.The sugar carried by the blood and the principal sugar used by the tissues.

Clinical significance-Presence of glucose in the urine leads to a condition called glycosuria in diabetes mellitus owing to raised blood glucose (hyperglycemia).

  • D-Fructose – is present in fruit juices, honey, obtained by the hydrolysis of cane sugar and of inulin (from the Jerusalem artichoke). Fructose can be changed to glucose in the liver and so used in the body.

Clinical significance- Hereditary fructose intolerance leads to fructose accumulation and hypoglycemia.

  • D-Galactose-Obtained by the hydrolysis of lactose. It can be changed to glucose in the liver and metabolized. Galactose can be synthesized in the mammary gland to make the lactose of milk. It is a constituent of glycolipids and glycoproteins.

Clinical significance- Failure to metabolize leads to galactosemia and cataract.

  • D-Mannose-Obtained from the hydrolysis of plant mannans and gums. A constituent of many glycoproteins.

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