Hepatic portal vein

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). 

The liver is a wedge-shaped organ of some 1.5 kg in adult humans, which, in terms of blood circulation, is interposed between the gastrointestinal tract and the rest of the body. The blood supply to the liver is from the hepatic portal vein (80%) and the hepatic artery (20%), the former bringing a rich supply of nutrients direct from the intestinal tract and the latter supplying the liver with oxygen. Blood drains from the liver by the hepatic vein. The position of the liver enables it to act as a processor of the absorbed nutrients, and to control their storage... 

Following resection of liver metastases, infusion of chemotherapy through the portal vein provides an additional adjuvant treatment approach. Historically 5-FU and floxuri-dine have been the agents used most commonly for hepatic portal vein infusion owing to their high metabolism in the liver. Although some studies demonstrate a decrease in recurrence rates, the value of portal vein infusion of chemotherapy for colon cancer remains to be determined.25 Table 88-4 summarizes adjuvant treatment recommendations for colon cancer. 

The hepatic artery supplies the liver with 300 ml/min of oxygenated blood from the aorta. The remaining 1050 ml/min of blood flow is delivered by the hepatic portal vein. This blood comes directly from the digestive tract. It is low in oxygen but contains a high concentration of nutrients absorbed from the intestines. 

Blood flowing from the intestines to the liver through the hepatic portal vein often contains bacteria. Filtration of this blood is a protective function provided by the liver. Large phagocytic macrophages, referred to as Kupffer cells, line the hepatic venous sinuses. As the blood flows through these sinuses, bacteria are rapidly taken up and digested by the Kupffer cells. This system is very efficient and removes more than 99% of the bacteria from the hepatic portal blood. 

Chylomicrons leave the absorptive cell by way of exocytosis. Because they are unable to cross the basement membrane of the blood capillaries, the chylomicrons enter the lacteals, which are part of the lymphatic system. The vessels of the lymphatic system converge to form the thoracic duct that drains into the venous system near the heart. Therefore, unlike products of carbohydrate and protein digestion that are transported directly to the liver by way of the hepatic portal vein, absorbed lipids are diluted in the blood... 

The use of hepatic portal vein-cannulated animals can be helpful in determining specific causes of poor bioavailability. After oral dosing, the total bioavailability of a compound is normally calculated as ... 

The mesenteric blood empties into the hepatic portal vein from where it is transported to the liver. At the liver, drug and metabolites can also be extracted from the portal blood and either metabolized or excreted unchanged into the bile. This is termed hepatic first-pass extraction. 

Concentration of compound in rat plasma obtained from hepatic portal vein (hpv). 

Different compartments pertaining to separate metabolic systems were assessed by selective injection as follows jugular vein to assess first-pass metabolism across lung, hepatic portal vein to assess hepatic first-pass metabolism, duodenum to assess intestinal mucosa metabolism, and carotid artery to assess immediate tissue distribution. 

Drugs absorbed through the gastrointestinal tract pass into the hepatic portal vein, which drains into the liver. The liver metabolizes the drug, which leads to reduction in the availability of the drug for interaction with receptors. This is called first pass metabolism. A schematic representation of the process of drug in the body is given in Fig. 5.7. 

Figure 1.16 A general plan of circulation of blood in a human. For details of the hepatic portal vein, see Chapter 6.

Bile salts In contrast to cholesterol, bile salts are absorbed mainly in the jejunum. They are returned to the liver through the hepatic portal vein (in association with proteins) and can thence be re-secreted into the bile. The transport of bile salts between liver and intestine is known... 

Figure 4.13 Uptake of bile acids in the jejunum. Bile adds (BA) and cholesterol (C) are secreted from the liver, via the bile, into the duodenum. Cholesterol is transported back into the blood, from the enterocyte, within chylomicrons. The latter enter the lymphatic system (i.e. the lacteals). Bile acids are absorbed from the jejunum into the hepatic portal vein for re-uptake into the liver.

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. 

Figure 6.28 The vascular link between the absorptive area of the intestine and the liver the hepatic portal vein. This vein is the only one that links capillaries in two organs and is fundamentally important in ensuring that the liver has access to all the nutrients, including the micronutrients, absorbed by the intestine. Note that the liver has two sources of blood.

Medium-chain acyl-CoA synthetase, which is present within the mitochondrial matrix of the liver, activates fatty acids containing from four to ten carbon atoms. Medium-chain length fatty acids are obtained mainly from triacylglycerols in dairy products. However, unlike long-chain fatty acids, they are not esterified in the epithelial cells of the intestine but enter the hepatic portal vein as fatty acids to be transported to the liver. Within the liver, they enter the mitochondria directly, where they are converted to acyl-CoA, which can be fully oxidised and/or converted into ketone bodies. The latter are released and can be taken up and oxidised by tissues. 

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