Chapter 32

• The hepatic artery supplies 45% to 50% of the liver’s oxygen requirements, and the portal vein supplies the remaining 50% to 55%.
• 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.
• 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), cholesterol, and pseudocholinesterase.
• 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.
• The PT, which is normally 11-14 sec, depending on the control value, measures the activity of fibrinogen, prothrombin, and factors V, VII, and X.
• The neuroendocrine stress response to surgery and trauma is characterized by elevated circulating levels of catecholamines, glucagon, and cortisol. Mobilization of carbohydrate stores and proteins results in hyperglycemia and a negative nitrogen balance (catabolism), respectively.
• All opioids can potentially cause spasm of the sphincter of Oddi and increase biliary pressure.
• When the results of liver tests are elevated postoperatively, the usual cause is underlying liver disease or the surgical procedure itself.

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, surgical anatomy divides the liver based on its blood supply. Thus, the right and left surgical lobes are defined 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 50,000-100,000 discrete anatomic units called lobules. Each lobule is composed of plates of hepatocytes arranged cylindrically around a centrilobular vein (Figure 32-1). Four to five portal tracts, composed of hepatic arterioles, portal venules, bile canaliculi, lymphatics, and nerves, surround each lobule.

###### Figure 32-1

The hepatic lobule.

In contrast to a lobule, an acinus, the functional unit of the liver, is defined by a portal tract in the middle and centrilobular veins at the periphery. Cells closest to the portal tract (zone 1) are well oxygenated; those closest to centrilobular veins (zone 3) receive the least oxygen and are most susceptible to injury.

Blood from hepatic arterioles and portal venules comingle in the sinusoidal channels, which lie between the cellular plates and serve as capillaries. These channels are lined by ...

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