Liver Anatomy and Function

Abstract

The liver’s primary physiologic functions include: lipid, carbohydrate, and protein metabolism; coagulation factor production; albumin production; detoxification of xenobiotics; storage of vitamins and glycogen; and bile processing and secretion. Disease processes affecting these functions are usually directed at hepatocytes, blood vessels, or bile ducts within the liver, and can produce a wide spectrum of liver disease. There are three basic morphologic appearances of the failed liver: massive hepatic necrosis, chronic liver disease resulting in cirrhosis, and hepatic dysfunction without overt necrosis. Of these, cirrhosis is the most common cause of liver related deaths and is the twelfth leading cause of death in the United States. The primary pathophysiologic influence behind the vast majority of decompensating events—such as gastrointestinal bleeding—in cirrhotic patients is portal hypertension, i.e. the increased resistance to portal blood flow that creates an increased gradient of pressure between the portal vein and the inferior vena cava. When the portal pressure increases beyond 12 mm Hg, patients are prone to develop ascites, varices, and hepatic encephalopathy. Transjugular intrahepatic portosystemic shunts (TIPS) alleviate portal hypertension, and therefore some of its complications, by lowering the portal pressure below the threshold of 12 mm Hg. Still, despite advances in medical care, many patients with cirrhosis require an evaluation for liver transplantation. The Child-Turcotte-Pugh score has been a mainstay for assessing severity of cirrhosis. Additionally, the Model for End-Stage Liver Disease (MELD) score—a value ranging from 6 to 40, derived from a patient’s serum creatinine, total bilirubin, and international normalized ratio (INR)—is used to predict mortality in patients with end stage liver disease and has been used for liver transplant allocation system in the United States. Since 2016, serum sodium was formally added to the MELD equation, based on data that hyponatremia is predictive of mortality in cirrhotic patients.