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LIVER

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Introduction to the Functions of the Liver

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The liver is a vital organ that performs a variety of important functions. It is unique among the internal organs for its ability to regenerate following tissue loss. Glucose homeostasis is maintained by the liver by way of glucose storage (as glycogen), glycogenolysis, and gluconeogenesis. In addition to glycogen, the liver is an important site for iron, copper, triglyceride, and lipid-soluble vitamin storage. A large number of serum proteins, such as albumin, clotting factors, and complement, are synthesized in the liver. Proper liver function is crucial for the catabolism of serum proteins and hormones and for the detoxification of exogenous substances, including many drugs. The liver is also the source of bile production, which is important for fat absorption within the small bowel.

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CASE 10-1

The patient is a 46-year-old man who sought medical attention for vague complaints of fatigue, joint pain, and upper abdominal pain. Laboratory studies were performed as part of the patient's evaluation and showed elevations of serum iron, serum transferrin saturation, and serum ferritin. There were mild elevations of aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Given these findings, a liver biopsy was performed and showed a prominent increase in iron accumulation within hepatocytes and early bridging fibrosis. A diagnosis of hemochromatosis was established. To evaluate for a genetic cause of hemochromatosis (i.e., primary hemochromatosis), analysis of the HFE gene was performed and showed a homozygous C282Y mutation, consistent with primary hemochromatosis (see section "Hemochromatosis" and Figure 10-16).

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Normal Anatomy and Histology of the Liver

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The liver is located in the right upper quadrant of the abdomen, immediately beneath the diaphragm. Two hepatic lobes are recognized: a larger right lobe and a smaller left lobe. The hepatic artery and portal vein provide the liver with a dual blood supply. The hepatic artery originates from the celiac axis and is the liver's source of more highly oxygenated blood. The portal vein is formed primarily by the convergence of the splenic vein and superior mesenteric vein. Because of its unique circulation, the portal vein provides the liver with metabolic substrates from the gut and provides a mechanism for ingested substances to be processed before entering the systemic circulation. The hepatic veins empty into the inferior vena cava and carry blood away from the liver and into the systemic circulation. The bile carrying ducts of the liver are called hepatic ducts. The right and left hepatic ducts empty into a common hepatic duct that merges with the cystic duct of the gallbladder to form the common bile duct (Figure 10-1).

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FIGURE 10-1

Anatomy of the liver. (A) Anterior and (B) posteroinferior. Source: Figure 26.18 in McKinley & O'Loughlin's Human Anatomy, 2nd ed.)

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From a microanatomical perspective, the ...

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