Lecture 4 - Liver Function Tests Flashcards
What are the main functions of the liver in the human body?
The liver serves several vital functions, including the metabolism and excretion of bilirubin; protein metabolism (deamination and synthesis of plasma proteins), fat, hormone, and carbohydrate metabolism; metabolism and excretion of drugs and alcohol, storage of vitamins and iron and activation of vitamin D.
How does the liver contribute to bilirubin metabolism, and what are the key forms of bilirubin in the bloodstream?
The liver plays a role in bilirubin metabolism. Bilirubin travels in the blood bound to albumin. In the liver, bilirubin is disassociated from albumin, conjugated with glucuronic acid to form conjugated bilirubin, and then excreted in bile. In the bloodstream, you have unconjugated and conjugated bilirubin.
Describe the process of bilirubin metabolism in the liver and its subsequent excretion.
Bilirubin metabolism involves the breakdown of red blood cells (RBCs), conversion of hemoglobin to bilirubin, transport of unconjugated bilirubin in the blood, conjugation in the liver to form conjugated bilirubin, excretion in bile, conversion to urobilinogen, and eventual excretion in urine and feces.
Explain the differences between unconjugated and conjugated bilirubin in terms of solubility and excretion.
Unconjugated bilirubin is insoluble in water, bound to albumin, and cannot be excreted in urine. Conjugated bilirubin is soluble in water, weakly bound to albumin, and can be excreted in urine.
What is pre-hepatic hyperbilirubinemia, and what conditions can lead to an increase in unconjugated bilirubin levels in the blood?
Pre-hepatic hyperbilirubinemia results from the overproduction of bilirubin. Conditions such as all forms of hemolytic anemia and ineffective erythropoiesis can increase unconjugated bilirubin levels in the blood.
Discuss hepatocellular hyperbilirubinemia, its causes, and the impact on unconjugated bilirubin levels.
Hepatocellular hyperbilirubinemia occurs due to hepatocellular damage or abnormal hepatocellular uptake, leading to an increase in unconjugated bilirubin levels. Causes include cirrhosis, hepatitis, and congenital enzyme deficiencies.
What is cholestatic hyperbilirubinemia, and how does it alter the ratio of conjugated to unconjugated bilirubin in the blood?
Cholestatic hyperbilirubinemia is characterized by a general impairment of bilirubin metabolism. It can result from intrahepatic (e.g., cirrhosis, hepatitis) or extrahepatic (e.g., gallstones, tumors) cholestasis. This condition can change the ratio of conjugated to unconjugated bilirubin in the blood.
How do liver enzymes, such as ALT and AST, serve as markers of hepatocellular injury, and how are they affected by various conditions and diseases?
ALT and AST are markers of acute hepatocellular injury. Conditions such as alcohol abuse can affect the AST:ALT ratio, while hepatitis may result in increased ALT levels. Cirrhosis can lead to elevated AST levels.
Explain the role of membrane enzymes in liver function and provide examples of these enzymes.
Membrane enzymes, including alkaline phosphatase (ALP) and gamma-glutamyl transferase (GGT), are important for liver function. ALP is made by cells lining bile canalicular membranes and can be released with the help of bilirubin. GGT is inducible and serves as a marker for various conditions, including excess alcohol consumption.
What are some of the proteins produced by the liver, and how can their levels in the blood provide insights into liver function and health?
The liver produces proteins such as albumin, alpha-fetoprotein (AFP), and coagulation factors. Decreased albumin levels can indicate chronic liver disease, while increased AFP levels may signal hepatocellular carcinoma. Altered coagulation factors can result in increased prothrombin time (PT).
When assessing liver function, what questions should be asked, and what aspects should be evaluated to determine the nature of liver dysfunction?
To assess liver function, three key questions should be considered: Are the hepatocytes damaged (assessed by AST and ALT levels)? Can the liver produce plasma proteins (indicated by albumin and PT)? Is there cholestasis (revealed by an increase in serum bilirubin and ALP)?
What are some common diseases and conditions associated with liver dysfunction.
Liver dysfunction can lead to cholestasis, jaundice, acute hepatitis (elevated ALT and AST), acute liver failure (hepatocellular damage with reduced plasma protein production), and cirrhosis (irreversible scarring and extensive liver damage).
Describe the role of stellate cells in the cirrhotic process and their function after liver injury.
Stellate cells, found in the space of Disse, are key players in the cirrhotic process. After liver injury, they become activated and produce proteins such as collagen, leading to the formation of fibrotic scar tissue in the liver.
Liver Biochemical testing is used to monitor…
Liver Biochemical testing is used to monitor:
Hepatocyte integrity - the activity of amino transferases
The synthetic capacity - measuring the concentration of key proteins
Conjugative capacity - Conjugated bilirubin
Free flow of bile - cholestasis
