Hepatic portal vein glucose

A hepatic portal vein glucose sensor was identified in the early 1980s (Shimizu et al., 1983). The... 

Water-soluble products of digestion are transported directly to the fiver via the hepatic portal vein. The fiver regulates die blood concentrations of glucose and amino acids. 

The digestible dietary carbohydrates yield glucose, galactose, and fructose that are transported via the hepatic portal vein to the hver where galactose and fructose are readily converted to glucose (Chapter 20). 

One is the glucose that is absorbed from the intestine and enters the blood in the hepatic portal vein from where some of it is taken np by the Uver and phosphorylated to form glncose 6-phosphate, which then stimulates the formation of glycogen (for discnssion of regulation of this process, see below). This is known as the direct pathway for glycogen synthesis. 

Glucose and amino acids leave the intestinal epithelial cells and enter the hepatic portal vein. Therefore, the liver is the first tissue through which these products of digestion pass. 

After a meal that contains protein, amino acids released by digestion (see Chapter 37) pass from the gut through the hepatic portal vein to the liver (see Fig. 38.2A). In a normal diet containing 60 to 100 g protein, most of the amino acids are used for the synthesis of proteins in the liver and in other tissues. Excess amino acids may be concerted to glucose or triacylglycerol. 

The liver is the first organ to receive blood that contains glucose absorbed from the intestine. The portal vein drains from the small intestine into the hepatic sinuses that are surrounded in a neat columnar fashion by hepatocytes. The arrival of glucose in the blood is detected by the p-cells in the pancreas, and they respond by secreting the peptide hormone insulin. Insulin facilitates glucose uptake by many cell types, from skeletal muscle to white blood cells (Fig. 11-4), but it has no effect on glucose uptake by the brain or red blood cells that rely on GLUT-1. 

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