Portal triad

Allergic reactions to drugs produce foci of necrosis that are scattered throughout the liver. Other agents cause severe (chlorpromazine) or mild (estrogens) cholestatic liver damage, including cholestasis and inflammation of the portal triad and hepatocellular necrosis. 

In vivo HMSC engraftment and migration Fischer rat MSCs were infused intraportally into the livers of other Fischer rats (2 million cells/rat) Results showed cells to persist for at least 28 days, being localized to the portal triad regions 643859... 

Figure 28.1. Comparison of structural liver lobule with functional acinar regions. The liver lobule is centered on the terminal hepatic venule (THV), also called the central vein, and assumes a roughly hexagonal shape with its vertices at the portal triads, which contain the portal vein (PV), hepatic artery (HA), and bile duct (BD). The liver acinus is centered upon the tract of blood vessels that branch from the hepatic artery and portal vein of the portal triads. Hepatocytes within the acinus are grouped within functional zones 1,2, and 3 located at increasing distances from the vascular tracts that interconnect adjacent portal triads.

Blood emerging from the portal tract filters through the network of sinusoidal channels that separate rows of hepatocytes on its way towards the central vein. The hepatocytes within the acinus can be subdivided into three zones according to their distance from the portal venule. Cells in close proximity to the portal triad are the first to receive the nutrient- and oxygen-rich blood, and are consequently most... 

Hepatic lobule and hepatic acinus are relatively well-accepted models to describe the structure and functional aspects of the liver. Histologically, the hepatic lobule is a hexagonal region of the liver parenchyma around the central vein. Typically, six portal triads, consisting of branches from the portal vein and hepatic artery as well as bile ductules, border the edge of the lobule. Cords of hepa-tocytes are arranged radially around the central vein and blood sinusoids form between them. The hepatic parenchyma is divided into three zones based on the proximity to... 

In addition to hepatic parenchymal cells which are hepatocytes, hepatocyte stem cells, termed oval cells, are reported to be located in the canals of Hering where bile canaliculi from the hepatic cords converge on bile ductules of the portal triad. It is postulated that new hepatocytes travel down hepatic cords to replace the aging and damaged zone 3 hepatocytes. 

Canaliculi enter canals of Hering in the portal triad and lead to intrahepatic bile ducts which coalesce to form the hepatic bile duct. The bile duct empties the bile into the gaU bladder which then is released into the duodenum. Bile that is excreted into the small intestine enhances nutrient uptake, protects enterocytes from oxidation, and facilitates excretion of xenobiotics and endogenous waste in the feces (Treinen-Moslen, 2001). 

A 50-year-old man developed recurrent sharp lower abdominal pain and nausea, having taken modified-release nicotinic acid 500-2000 mg/day for 8 weeks for hypercholesterolemia. He had a low-grade fever, tachycardia, and hypotension. Abdominal ultrasonography showed a markedly hypoechoic liver of normal size, with relatively echogenic conspicuous portal triads. Aspartate transaminase activity and prothrombin time were raised. Nicotinic acid was withdrawn and the signs and symptoms resolved within several days. 

The functional anatomical unit of the hver is the acinus, adjacent to the portal triad, which consists of a branch of the portal vein, hepatic artery, and bile duct. Each acinus is a diamond-shaped mass of liver parenchyma that is supplied by a terminal branch of the portal vein and of the hepatic artery and drained by a terminal branch of the bile duct. The blood vessels radiate toward the periphery, forming sinusoids, which perfuse the liver and ultimately drain into the central (terminal) hepatic vein (Figure 47-2). The sinusoids... 

Treatment No of focl/cm3 % of hepatocytes labeled % of non-parenchymal cells outside portal triad labeled... 

Schematic representation of the radial architecture of the plates formed by the liver cells. Blood from the portal vein and the hepatic artery flows into sinusoids and eventually enters the central vein. The bile canaliculi are located between the liver cells. Bile flows in the opposite direction and empties into the bile duct in portal triads. [Reproduced with permission from A. W. Ham Histology, 8th ed., J. B. Lippincott, Philadelphia, 1979.]...

Arterial and venous blood from the portal triad passes through the hepatic lobules to the central veins via the hepatic sinusoids. After passing through the hepatic lobules, blood collects in the central veins, which ultimately coalesce into the hepatic veins, which then enter the inferior vena cava. 

The lobes of the liver are divided into smaller lobules with a roughly hexagonal arrangement of hepatocytes around a central vein. At the vertices of the lobules are bile ducts, terminal branches of the hepatic artery, and portal veins—termed the portal triad. Connective stromal tissues extend throughout the liver, providing support for cells and routes for blood vessels, lymphatic vessels, and bile ducts. The hepatocytes form groups of cells around small branches of the portal vein, hepatic arteriole, bile duct, lymph vessel, and nerves this functional unit is called an acinus (plural acini). The acini form part of a larger structure, which can be divided into three zones ... 

The diverse metabolic activities of the liver make it susceptible to solvent induced in-jiuy, particularly from reactive intermediates which damage cellular macromolecules. The microscopic anatomy of the liver provides an explanation for this susceptibility. The basic unit of the liver is the hepatic lobule which consists of a central vein surrounded radially by sinusoids of liver cells (hepatocytes). Portal triads consisting of a hepatic artery, a hepatic vein and a bile canniliculus are located at the periphery. Liver cells closest to the vascular... 

Fig. 1 shows a liver biopsy of a 7 week old infant (J.M.) with intestinal atresia, who had been treated with parenteral nutrition for the previous 6 weeks. There is evidence of cholestasis and infiltration of the portal triad. The patient was rebiopsied at 16 weeks of age while still continuing on intravenous nutrition. A round cell infiltrate in the portal area with some fibrous tissue was noted. A third biopsy performed at six months of age while the child was still being maintained on parenteral nutrition revealed the continued presence of fibrous tissue and a round cell infiltrate in the portal triad. 

Fig. 1. Section of a percutaneous liver biopsy from patient J.M. at 7 weeks of age after 6 weeks of parenteral nutrition. Note the small l3nnphocytic infiltrate extending beyond the portal triad. H E stain x 100.

Zone 1 is closest to the portal triad and receives the highest exposure to toxicants in the blood. Enzymes of inlaiiiedMryinetaboKsm are prominent in ad-... 

Zone 3 isiiarthestfrom the portal triad. Thb zone has the lowest oxygen tension and contains the greatest concenbalion of mkrosomal MFOs, which can alter the toxicity of xenobk cs. 

RCURE 8-1. Comparaiive structural arxl functional features of tfte Kver. In tfie hexagonal lobule model, die central vein (CVO receives blood from the portal vein via die hepatic sinusoids. 69e, on the otfier hand, flows from die c itral vein toward the portal triad (P7). The centrilobular area, whm die central vein b located, b the least ox) enated area arid contains the highest concentration of mixed fwioion oxidases (MFOs). In die functional (acinar) model, the various zones (1.2. and 3) are characteri d by dtfferent leveb of blood flow, oxidative enzymes, arxl MFOs. 

Direction rrf bile flow. In the bile canaliculi, bile flows from the central vein toward the portal triad sinusoidal bltxxf flmv occurs from the portal vein to the central vein. 

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