Hepatic portal vein amino acids

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 liver is uniquely situated to process and distribute dietary nutrients because the venous drainage of the gut and pancreas passes through the hepatic portal vein before entry into the general circulation. Thus, after a meal, the liver is bathed in blood containing absorbed nutrients and elevated levels of insulin secreted by the pancreas. During the absorptive period, the liver takes up carbohydrates, lipids, and most amino acids. These nutrients are then metabolized, stored, or routed to other tissues. Thus, the liver smooths out potentially broad fluctuations in the availability of nutrients for the peripheral tissues. 

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. 

Dietary proteins are cleaved to amino acids by proteases (see Fig. 2.2, circle 3). Pepsin acts in the stomach, and the proteolytic enzymes produced by the pancreas (trypsin, chymotrypsin, elastase, and the carboxypeptidases) act in the lumen of the small intestine. Aminopeptidases and di- and tripeptidases associated with the intestinal epithelial cells complete the conversion of dietary proteins to amino acids, which are absorbed into the intestinal epithelial cells and released into the hepatic portal vein. 

The amino acids derived from dietary proteins travel from the intestine to the liver in the hepatic portal vein (see Fig. 2.2, circle 3). The liver uses amino acids for the synthesis of serum proteins as well as its own proteins, and for the biosynthesis of nitrogen-containing compounds that need amino acid presursors, such as the... 

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. 

In summary, that enters the urea cycle is produced in the body by deamination or deamidation of amino acids (see Fig. 38.5). A significant amount of NH4 is also produced by bacteria that live in the lumen of the intestinal tract. This ammonium ion enters the hepatic portal vein and travels to the liver. 

As shown in Figure 4.2, each villus has both blood capillaries, which drain into the hepatic portal vein, and a lacteal, which drains into the lymphatic system. Water-soluble products of digestion (carbohydrates and amino acids) are absorbed into the blood capillaries, and the liver has a major role in controlling the availability of the products of carbohydrate and protein digestion to other tissues in the body. As discussed in section 4.3.3.2, lipids are absorbed into the lacteals the lymphatic system joins the bloodstream at the thoracic duct, and extrahepatic tissues are exposed to the products of lipid digestion uncontrolled by the liver, which functions to clear the remnants from the circulation. 

BLOOD. Most of the low molecular weight (small) products of digestion are absorbed and transported by the blood. These nutrients include water, salts, glycerol, amino acids, short-chain fatty acids, monosaccharides, and certain vitamins. These materials are absorbed into the capillary system of the intestine. The capillary network drains into the venous system, eventually entering the portal vein of the liver. From the liver, the nutrients then travel through the hepatic veins which, in turn, enter the main systemic vein—the vena cava. 

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