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KEY CONCEPTS

KEY CONCEPTS

  • Image not available. The hepatic artery supplies about 25% of the blood supply but 45% to 50% of the liver’s oxygen requirements, and the portal vein supplies 75% of the blood supply and the remaining 50% to 55% of oxygen requirements.

  • Image not available. All coagulation factors, with the exception of factor VIII and von Willebrand factor, are produced by the liver. Vitamin K is a necessary cofactor in the synthesis of prothrombin (factor II) and factors VII, IX, and X.

  • Image not available. Many “liver function” tests, such as serum transaminase measurements, reflect hepatocellular integrity more than hepatic function. Liver tests that measure hepatic synthetic function include serum albumin, prothrombin time (PT) or international normalized ratio (INR), serum cholesterol, and plasma pseudocholinesterase.

  • Image not available. Albumin values less than 2.5 g/dL are generally indicative of chronic liver disease, acute stress, or severe malnutrition. Increased losses of albumin in the urine (nephrotic syndrome) or the gastrointestinal tract (protein-losing enteropathy) can also produce hypoalbuminemia.

  • Image not available. The PT, which normally ranges between 11 and 14 s, depending on the control value, measures the activity of fibrinogen, prothrombin, and factors V, VII, and X. A prolonged INR reflects a patient with a dysfunctional liver. The effect on coagulation will depend on the balance between coagulation and anticoagulation factors. If production of protein C, protein S, and antithrombin 3, are affected more than the coagulation factors a normal or hypercoaguable state might exist. The INR was developed to monitor the effect of warfarin and that does not affect the anticoagulant factors.

  • Image not available. Operative procedures near the liver can reduce hepatic blood flow up to 60%. Although the mechanisms are not clear, they most likely involve sympathetic activation, local reflexes, and direct compression of vessels in the portal and hepatic circulations.

  • Image not available. The neuroendocrine stress response to surgery and trauma is characterized by elevated circulating levels of catecholamines, glucagon, and cortisol and results in mobilization of carbohydrate stores and proteins, causing hyperglycemia and a negative nitrogen balance (catabolism).

  • Image not available. All opioids can potentially cause spasm of the sphincter of Oddi and increase biliary pressure.

  • Image not available. When liver tests are abnormal postoperatively, the usual cause is underlying liver disease or the surgical procedure itself.

FUNCTIONAL ANATOMY

The liver is the heaviest organ in the body, weighing approximately 1500 g in adults. It is separated by the falciform ligament into right and left anatomic lobes; the larger right lobe has two additional smaller lobes at its posterior–inferior surface, the caudate and quadrate lobes.

In contrast, surgeons describe the liver based on its blood supply. Thus, the right and left surgical lobes are defined by anatomists by the point of bifurcation of the hepatic artery and portal vein (porta hepatis); the falciform ligament therefore divides the left surgical lobe into medial and lateral segments. Surgical anatomy defines a total of eight segments.

The liver is made up of 50,000 to 100,000 discrete anatomic units called lobules. Each lobule ...

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