The following points highlight the top three sources of blood glucose. The sources are: 1. From Carbohydrates of the Diet 2. From Various Glucogenic Compounds 3. From Liver Glycogen by Glycogenolysis.
Blood Glucose: Source # 1. From Carbohydrates of the Diet:
a. Most carbohydrates in the diet after digestion form glucose, galactose or fructose which are absorbed into the portal vein.
b. In the liver, galactose and fructose are converted to glucose.
Blood Glucose: Source # 2. From Various Glucogenic Compounds:
In the skeletal muscle, glucose is oxidized to lactic acid which is transported by blood to the liver and kidney where glucose is reformed and undergoes oxidation in the tissues via the circulation. This process is known as the “Con Cycle” or “Lactic Acid Cycle”.
In the adipose tissue, the synthesis of triacylglycerol takes place from glycerol which is derived initially from blood glucose. Acylglycerols of adipose tissue continually undergo hydrolysis to form free glycerol which diffuses out of the tissue into the blood.
This is converted back to glucose in the liver and kidney by gluconeogenesis. Hence, a continuous cycle exists in which glucose is transported to adipose tissue from the liver and kidney and glycerol is returned to be synthesized into glucose by the liver and kidney.
3. During starvation, the amino acid, alanine, is transported from muscle to liver with an effect of a net transfer of amino nitrogen from muscle to liver and of free energy from liver to muscle. The energy required for the synthesis of glucose from pyruvate in the liver is derived from fatty acid oxidation.
Blood Glucose: Source # 3. From Liver Glycogen by Glycogenolysis:
Glucose is formed in the liver from glycogen by phosphorylase and de-branching enzyme and also by glucose-6-phosphatase by the effect of the hormone epinephrine and glucagon.