The endproducts of carbohydrate digestion absorbed into the blood and taken to the liver by hepatic portal vein are four monosaccharide sugar ( C6H12O6) viz, glucose, fructose mannose and galactose. Liver cells readily convert fructose , mannose and galactose into D glucose .Hence, mainly Dglucose circulates in the blood. Normal glucose concentration inhuman blood is 100 milligrams per100 millilitres of blood i.e. about 0.1% of blood . After meals blood sugar level may rise upto 0.14% depending upon the amount of carbohydrates digested from food. During fasting 8 to10 hours after meal , glucose level in blood falls to about 60to 70 mg 100 mi of blood. Glucose is transported into the cells across the plasma membrane by facilitated diffusion through carrier proteins.
The cellular metabolism of carbohydrates in the body is divisible into five main aspects glycogen glycogenolysis , anabolism and lipogenesis, gluconeogenesis amd catabolic breakdown.