Portal vein

FIGURE 23.21 The portal vein system carries pancreatic secretions snch as insnlin and glncagon to the liver and then into the rest of the circnlatory system. 

Pfluggehar,/, plowshare (Anat.) vomer, Pfortader, /, portal vein,... 

DeFeo, T. T., and Morgan, K. G. (1986). A comparison of two different indicators quin 2 and aequorin in isolated single cells and intact strips of ferret portal vein. Pfluegers Arch. 406 427-429. 

Figure 13 presents a schematic diagram for drug absorption from the peritoneal cavity. As mentioned above, particles (e.g., erythrocytes, bacteria, colloidal gold, and liposomes) which are not able to pass capillary membranes are removed from the peritoneal cavity via the lymphatic system (Fig. 13, I and II). Relatively low molecular weight compounds (e.g., drugs) are exclusively absorbed via splenic blood capillaries into the portal vein (Fig. 13, III).

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). 

In intestinal cells, carotenoids can be incorporated into CMs as intact molecules or metabolized into mainly retinol (or vitamin A), but also in retinoic acid and apoc-arotenals (see below for carotenoid cleavage reactions). These polar metabolites are directly secreted into the blood stream via the portal vein (Figure 3.2.2). Within intestinal cells, retinol can be also esterified into retinyl esters. 

For the majority of drugs, the preferred administration route is by oral ingestion which requires good intestinal absorption of drug molecules. Intestinal absorption is usually expressed as fraction absorbed (FA), expressing the percentage of initial dose appearing in a portal vein [15]. 

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... 

The portal vein is the primary vessel leading into the liver it receives deoxygenated venous blood flow from the small intestine, stomach, pancreas, and spleen (Fig. 19-1). The inflow from these organ systems accounts for approximately 75% of... 

Portal hypertension is a consequence of increased resistance to blood flow through the portal vein. Increased resistance is usually due to restructuring of intrahepatic tissue (sinusoidal damage) but may also be caused by presinusoidal damage such as portal vein occlusion from trauma, malignancy, or thrombosis. A third (and the least common) mechanism is outflow obstruction of the hepatic vein. This latter damage is posthepatic, and normal liver structure is maintained. This chapter will focus on portal hypertension caused by intrahepatic damage from cirrhosis. 

In contrast to the posterior pituitary lobe, the anterior pituitary lobe is under the control of several releasing and inhibiting hormones secreted from the hypothalamus via a portal vein system. The anterior pituitary lobe, in turn, synthesizes and secretes six major hormones. Figure 43-1 summarizes the physiologic mediators and effects of each of these hormones. 

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. 

Portal hypertension Increased blood pressure within the portal vein that supplies the liver. 

Fig. 5 Mean blood levels of lidocaine hydrochloride in live beagles after exponential IV infusion through a peripheral vein ( ) and in the portal vein ( ). Vertical bars represent standard errors of the mean. (From Ref. 13.)...

The adenohypophysis does not have a direct anatomical connection with the hypothalamus therefore, regulation of hormone secretion by way of neuronal signals is not possible. Instead, these two structures are associated by a specialized circulatory system and the secretion of hormones from the adenohypophysis is regulated by hormonal signals from the hypothalamus (see Figure 10.2). Systemic arterial blood is directed first to the hypothalamus. The exchange of materials between the blood and the interstitial fluid of the hypothalamus takes place at the primary capillary plexus. The blood then flows to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Portal veins are blood vessels that connect two capillary beds. The second capillary bed in this system is the secondary capillary plexus located in the adenohypophysis. 

Located in close proximity to the primary capillary plexus in the hypothalamus are specialized neurosecretory cells. In fact, the axons of these cells terminate on the capillaries. The neurosecretory cells synthesize two types of hormones releasing hormones and inhibiting hormones (see Table 10.2). Each of these hormones helps to regulate the release of a particular hormone from the adenohypophysis. For example, thyrotropin-releasing hormone produced by the neurosecretory cells of the hypothalamus stimulates secretion of thyrotropin from the thyrotrope cells of the adenohypophysis. The hypo-thalamic-releasing hormone is picked up by the primary capillary plexus travels through the hypothalamic-hypophyseal portal veins to the anterior pituitary leaves the blood by way of the secondary capillary plexus and exerts its effect on the appropriate cells of the adenohypophysis. The hypophyseal hormone, in this case, thyrotropin, is then picked up by the secondary capillary plexus, removed from the pituitary by the venous blood, and delivered to its target tissue. 

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. 

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