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Portal circulation

Food vitamin B 2 appears to bind to a saUvary transport protein referred to as the R-protein, R-binder, or haptocorrin. In the stomach, R-protein and the intrinsic factor competitively bind the vitamin. Release from the R-protein occurs in the small intestine by the action of pancreatic proteases, leading to specific binding to the intrinsic factor. The resultant complex is transported to the ileum where it is bound to a cell surface receptor and enters the intestinal cell. The vitamin is then freed from the intrinsic factor and bound to transcobalamin II in the enterocyte. The resulting complex enters the portal circulation. [Pg.113]

Aspirin has been remarkably successful in the treatment of the pain and swelling of inflammatory disease and in fact, an estimated 45,000 tons of aspirin are still consumed each year. This success resulted in the syntheses of many other aspirin-like drugs , now referred to as NSAIDs. Aspirin, however, continues to have a unique use in the prevention of thrombosis. Since it produces irreversible inhibition of COX-1 by acetylation of serine at position 530 in the active site, a daily low dose of aspirin will cause a cumulative inhibition of COX-1 in platelets, in the portal circulation. A gradual inhibition of platelet aggregation occurs, reducing the possibility of occlusion of coronary or cerebral vessels by platelet thrombi. However, there are no systemic... [Pg.404]

Intestinal permeation describes the ability of drugs to cross the intestinal mucosa separating the gut lumen from the portal circulation. It is an essential... [Pg.499]

Although products of fat digestion, including cholesterol, are absorbed in the first 100 cm of small intestine, the primary and secondary bile acids are absorbed almost exclusively in the ileum, and 98—99% are returned to the liver via the portal circulation. This is known as the enterohepatic circulation (Figure 26—6). However, lithocholic acid, because of its insolubility, is not reabsorbed to any significant extent. Only a small fraction of the bile salts escapes absorption and is therefore eliminated in the feces. Nonetheless, this represents a major pathway for the elimination of cholesterol. Each day the small pool of bile acids (about 3-5 g) is cycled through the intestine six to ten times and an amount of bile acid equivalent to that lost in the feces is synthesized from cholesterol, so that a pool of bile acids of constant size is maintained. This is accomplished by a system of feedback controls. [Pg.227]

Figure 5,4 Pharmacokinetics. The absorption distribution and fate of drugs in the body. Routes of administration are shown on the left, excretion in the urine and faeces on the right. Drugs taken orally are absorbed from the stomach and intestine and must first pass through the portal circulation and liver where they may be metabolised. In the plasma much drug is bound to protein and only that which is free can pass through the capillaries and into tissue and organs. To cross the blood brain barrier, however, drugs have to be in an unionised lipid-soluble (lipophilic) form. This is also essential for the absorption of drugs from the intestine and their reabsorption in the kidney tubule. See text for further details... Figure 5,4 Pharmacokinetics. The absorption distribution and fate of drugs in the body. Routes of administration are shown on the left, excretion in the urine and faeces on the right. Drugs taken orally are absorbed from the stomach and intestine and must first pass through the portal circulation and liver where they may be metabolised. In the plasma much drug is bound to protein and only that which is free can pass through the capillaries and into tissue and organs. To cross the blood brain barrier, however, drugs have to be in an unionised lipid-soluble (lipophilic) form. This is also essential for the absorption of drugs from the intestine and their reabsorption in the kidney tubule. See text for further details...
FIGURE 41-1. Hypothalamic-pituitary-thyroid axis. Thyrotropinreleasing hormone (TRH) is synthesized in the neurons within the paraventricular nucleus of the hypothalamus. TRH is released into the hypothalamic-pituitary portal circulation and carried to the pituitary, where it activates the pituitary to synthesize and release thyrotropin (TSH). TSH activates the thyroid to stimulate the synthesis and secretion of thyroxine (T4) and triiodothyronine (T3). T4 and T3 inhibit TRH and TSH secretion, closing the feedback loop. [Pg.669]

E. histolytica invades mucosal cells of colonic epithelium, producing the classic flask-shaped ulcer in the submucosa. The trophozoite toxin has a cytocidal effect on cells. If the trophozoite gets into the portal circulation, it will be carried to the liver, where it produces abscess and periportal fibrosis. Liver abscesses are more common in men than women and are rarely seen in children. Amebic ulcerations can affect the perineum and genitalia, and abscesses may occur in the lung and brain. [Pg.1141]

Some forms of invasive candidiasis are dominated by deep organ infection and may never be detected by blood cultures. Chronic disseminated candidiasis or hepatosplenic candidiasis is a unique form of candidemia seen after recovery from neutropenia. Candidemia during the period of neutropenia may be initially localized to the portal circulation with dissemination to contiguous organs. After recovery of neutrophils, an inflammatory response is seen against areas of focal infection in the liver and spleen. This inflammatory response produces abdominal pain that is associated with... [Pg.1219]

Diisopropyl methylphosphonate is initially distributed to the liver by way of the portal circulation after absorption from the intestines, and then to the kidneys for excretion (Hart 1976). High concentrations of radiolabel were detected in the urinary bladder itself, exclusive of any urine of mice at 15 minutes and persisted for up to 6 hours. A similar pattern of distribution to the liver, kidney, and urinary bladder was seen in rats over the first 6 hours after oral administration of diisopropyl methylphosphonate. [Pg.68]

The fraction of the orally administered dose that is bioavailable to the systemic circulation (Fsystemjc) is dependent upon the fraction of the dose that is released from the dosage form (/released), multiplied by the fraction that is absorbed into the portal circulation on its way to the liver (/absorbed this is the fraction that escapes gut metabolism), multiplied by the fraction of the dose that escapes the hepatic first-pass effect (/hepatic)- Since this is a multiplicative process if, for... [Pg.68]

It was determined that 9.5% of an oral 80-mg dose of verapamil was absorbed in a 70-kg test subject. However, because of extensive bio transformation during its first pass through the portal circulation, the bio availability of verapamil was only 25%. Assuming a liver blood flow of 1500 mLAmin, the hepatic clearance of verapamil in this situation was... [Pg.31]

The hypothalamic releasing factors regulate release of the anterior pituitary trophic hormones. As summarized in Figure 52-1, the releasing factors are produced in various neuronal groups within the hypothalamus and are transported to the median eminence for release into the portal circulation to the anterior pituitary. Neurons in the hypothalamus also produce the hormones oxytocin and vasopressin, which are released by the posterior pituitary into the blood. Therefore, it is not surprising that behavior and experience, which influence the hypothalamus, sometimes alter the secretion of these hypothalamic releasing factors and hormones. [Pg.844]

Intraperitoneal Route. Kruger et al. (1962) demonstrated the efficiency of absorption of some chemicals injected IP, while Lukas et al. (1971) showed that compounds administered IP are absorbed primarily through the portal circulation. [Pg.453]

Chemicals that are metabolized rapidly by the liver cannot be given for systemic effect by the enteral route because the portal circulation carries them directly to the liver. For example, lidocaine, a drug of value in controlling cardiac arrhythmias, is absorbed well from the gut, but is completely inactivated in a single passage through the liver. [Pg.457]

Drugs that are orally administered often undergo first-pass metabolism. This involves their (generally partial) metabolism in the liver following their entry from the gastrointestinal tract via the portal circulation. This... [Pg.90]

Intestinal epithelial cells take up these compounds, process them further, and then release them into the hepatic portal circulation. [Pg.58]

Fatty acids released from visceral fat move through the hepatic portal circulation directly to the liver, leading to altered hepatic fat metabolism. [Pg.61]

Amino acids are then secreted into the hepatic portal circulation. [Pg.122]

Curcumin (diferuloylmethane) has very low oral bioavailability, but is rapidly absorbed and low nanomolar levels of the parent compound and its glucuronide and sulfate conjugates can be detected in human plasma and portal circulation after very high (nondietary) intakes (3.6g/day for 1 week). Metabolic reduction occurs in the liver, and glutathione adducts have been observed in vitro ... [Pg.329]

A percentage of xenobiotics absorbed in the gastrointestinal cells may be biotransformed prior to entering the circulatory system the balance is transported as the parent compound. The absorbed compounds may enter the circulation either via the lymphatic system, which eventually drains into the bloodstream, or via the portal circulation, which carries them to the liver. [Pg.123]

When drugs are administered orally, they typically are absorbed in the small bowel, enter the portal circulation, and pass through the liver. Both CYP enzymes in the bowel wall and in the hepatocytes can metabolize a fraction of the drug before it reaches the systematic circulation (i.e., first-pass metabolism or first-pass effect). The extent of this effect can be broadly altered by diseases (e.g., cirrhosis, portacaval shunting, persistent hepatitis, congestive heart failure), and by some drugs (e.g., alcohol, ketaconazole, fluoxetine) influencing the peak concentrations achieved and the ratio of the parent compound to metabolites ( 11, 19, 20). [Pg.35]

Once first-pass metabolism has occurred, metabolites are excreted into the bile and then the small bowel. Those that are lipid soluble are reabsorbed into the portal circulation, eventually entering the systemic circulation. These metabolites may have a similar or substantially different pharmacological profile from their parent drug. For example, chlorpromazine undergoes extensive hepatic biotransformation and has 168 theoretical metabolites, 70 of which have been identified in plasma and... [Pg.35]

Enterohepatic recirculation The reabsorption of drug and/or metabolites from the small bowel into the portal circulation after first pass metabolism has occurred. Such recirculation contributes to the total amount of drug and/or metabolites, which eventually enters the systemic circulation (e.g., demethylated and hydroxylated metabolites of tricyclic antidepressants). [Pg.43]


See other pages where Portal circulation is mentioned: [Pg.1273]    [Pg.160]    [Pg.229]    [Pg.112]    [Pg.1512]    [Pg.39]    [Pg.39]    [Pg.136]    [Pg.252]    [Pg.265]    [Pg.42]    [Pg.46]    [Pg.893]    [Pg.568]    [Pg.191]    [Pg.17]    [Pg.82]    [Pg.44]    [Pg.66]    [Pg.142]    [Pg.46]    [Pg.111]    [Pg.286]    [Pg.354]    [Pg.33]    [Pg.37]    [Pg.34]   
See also in sourсe #XX -- [ Pg.736 ]




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