GLUCOSE IN HEALTH AND IN
DISEASES
Most digestible carbohydrates in the diet ultimately form glucose. The dietary carbohydrates that are actively digested contain glucose, galactose, and fructose residues that are released in the intestine. These are transported to the liver via the hepatic portal vein. Galactose and fructose are readily converted to glucose in the liver.
Another source of Blood glucose is glucogenic compounds that undergo gluconeogenesis. Gluconeogenesis is the mechanism for converting non -carbonhydrates to glucose or glycogen. It provide the body with glucose when carbohydrate is not available from the diet. The important substrates are glucogenic amino acids, lactate, glycerol and propionate .
Glucose is also formed from liver glycogen by glycogenolysis. umans and many mammals is set within the range 4.5-5.5 mmol/L. After the ingestion of a carbohydrate meal, it may rise to .5-7.2 mmol/L. During fasting, the levels fall to around 3.3-3.9mmol/L The blood glucose level in birds is considerably higher 14.0 mmol/L and in ruminants considerably lower (approximately 2.2. mmol/L in sheep and 3.3mmol/L in Cattle).
These lower normal levels appear to be associated with the fact that ruminants ferment virtually all dietary carbohydrate to lower (volatile) Fatty acids, and these largely replace glucose as the main metabolic fuel of the tissues in the fed condition. In the rat, it has been estimated that the rate of uptake of glucose and rate of out put are equal at a hepatic portal vein blood glucose concentration of 8.3 mmol/L (Harper’s 25th Edition pp 215).
When the blood glucose rises to relatively high levels, the kidney also exert a regulatory effect. Glucose is continuously filtered by the glomeruli but is ordinarily returned completely to the blood by the reabsorptive system of glucose against its concentration gradient is linked to the provision of ATP in the tubular cells. The capacity of the tubular system to reabsorb glucose is limited to a rate of about 350mg/min. When the blood levels of glucose are elevated, the glomerular filtrate may contain more glucose than can be rebsorbed; the excess passes into the urine to produce glycosuria. In normal individuals, glycosuria occurs when the venous blood glucose concentration exceeds 9.5-10.0mmol/L. This is called the renal threshold of glucose.Glycogen represents the principal storage form of carbohydrate in mammalian body present mainly in the liver and muscle.
