Liver Enzymes Overview: AST and ALT Functions
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Questions and Answers

What condition is associated with an ALT elevation higher than AST due to its longer half-life?

  • Muscular Dystrophy
  • Acute Hepatocellular Disorders (correct)
  • Viral Hepatitis
  • Congestive Heart Failure
  • Which isoenzyme of alkaline phosphatase is predominantly found in the prostate?

  • Bone ALP
  • Liver ALP
  • Placental ALP
  • Acid Phosphatase (correct)
  • What is the optimum pH range for alkaline phosphatase activity?

  • 11.0 - 12.0
  • 5.0 - 6.0
  • 9.0 - 10.0 (correct)
  • 7.0 - 8.0
  • What method is NOT commonly used to differentiate the isoenzymes of alkaline phosphatase?

    <p>Molecular cloning</p> Signup and view all the answers

    In what situation is AST usually greater than ALT in acute hepatocellular injury?

    <p>Alcohol-induced injury</p> Signup and view all the answers

    Which tissue does NOT primarily source alkaline phosphatase activity?

    <p>Lung</p> Signup and view all the answers

    Which statement regarding the De Ritis ratio is correct?

    <p>It indicates a higher AST than ALT in hepatocellular injury.</p> Signup and view all the answers

    Which cofactor is essential for the activity of both alkaline and acid phosphatases?

    <p>Magnesium</p> Signup and view all the answers

    What is the primary function of Aspartate Aminotransferase (AST)?

    <p>Transfer of amino groups between aspartate and alpha-keto acids</p> Signup and view all the answers

    Which tissue has the highest source of Alanine Aminotransferase (ALT)?

    <p>Liver</p> Signup and view all the answers

    What cofactor is used by both AST and ALT enzymes?

    <p>Pyridoxal phosphate (Vitamin B6)</p> Signup and view all the answers

    During an Acute Myocardial Infarction (AMI), how long does it typically take for AST levels to peak?

    <p>6-8 hours</p> Signup and view all the answers

    Which of the following statements about AST isoenzyme fractions is true?

    <p>The cytoplasmic form increases during cellular necrosis</p> Signup and view all the answers

    For which condition is AST diagnostic significance are limited?

    <p>Acute Myocardial Infarction (AMI)</p> Signup and view all the answers

    Which tissue is NOT a source of Aspartate Aminotransferase (AST)?

    <p>Thyroid</p> Signup and view all the answers

    Which of the following best describes the role of ketoacids formed by AST?

    <p>Oxidized for energy production in the tricarboxylic acid cycle</p> Signup and view all the answers

    What condition typically leads to an increased synthesis of alkaline phosphatase (ALP)?

    <p>Cholestasis</p> Signup and view all the answers

    Which of the following is NOT a potential cause of extrahepatic cholestasis?

    <p>Viral hepatitis</p> Signup and view all the answers

    Which triad is associated with cholangitis?

    <p>Charcot’s triad</p> Signup and view all the answers

    What condition is indicated by an increase in alkaline phosphatase during normal pregnancy?

    <p>Preeclampsia</p> Signup and view all the answers

    Which enzyme is primarily used as a marker for hairy cell leukemia?

    <p>Acid Phosphatase</p> Signup and view all the answers

    In which scenario would acid phosphatase activity be particularly useful?

    <p>Detecting prostatic carcinoma</p> Signup and view all the answers

    Which alkaline phosphatase isoenzyme is primarily associated with hepatobiliary conditions?

    <p>Liver ALP</p> Signup and view all the answers

    What is the impact of hypophosphatasia on alkaline phosphatase levels?

    <p>Decreased levels</p> Signup and view all the answers

    Which factor is likely to elevate acid phosphatase activity in vaginal washings?

    <p>Seminal fluid presence</p> Signup and view all the answers

    What indicates bone ALP activity after heating serum at 56 degrees Celsius for 10 minutes?

    <p>Residual activity less than 20%</p> Signup and view all the answers

    Which agent inhibits intestinal ALP and placental ALP more effectively than liver and bone ALP?

    <p>Phenylalanine</p> Signup and view all the answers

    Which isoenzyme is most heat stable, resisting denaturation at 65 degrees Celsius for 30 minutes?

    <p>Regan Isoenzyme</p> Signup and view all the answers

    Which alkaline phosphatase isoenzyme is associated with metastatic carcinoma of pleural surfaces?

    <p>Nagao Isoenzyme</p> Signup and view all the answers

    What is the distinguishing feature of placental ALP compared to other isoenzymes in terms of heat stability?

    <p>Most heat stable at 65 degrees Celsius</p> Signup and view all the answers

    Which of the following factors indicates the presence of hepatobiliary disorders based on alkaline phosphatase levels?

    <p>Levels 3-10 times ULN</p> Signup and view all the answers

    Which factor is used to differentiate alkaline phosphatase isoenzymes through chemical inhibition?

    <p>Phenylalanine</p> Signup and view all the answers

    Study Notes

    Liver Enzymes Overview

    • AST (Aspartate Aminotransferase) and ALT (Alanine Aminotransferase) are critical liver enzymes involved in amino acid metabolism.
    • E.C. number classification: AST (2.6.1.1) and ALT (2.6.1.2).

    Aspartate Aminotransferase (AST)

    • Function: Transfers amino groups between aspartate and alpha-keto acids, forming oxaloacetate and glutamate.
    • Former names: Serum glutamic-oxaloacetic transaminase (SGOT or GOT).
    • Cofactor: Pyridoxal phosphate (Vitamin B6).
    • Sources: Highest in cardiac tissue, followed by liver and skeletal muscle.
    • Intracellular concentration is significantly higher than in plasma.

    Diagnostic Significance of AST

    • Primarily used to evaluate hepatocellular disorders and muscle conditions.
    • In acute myocardial infarction (AMI): rises within 6-8 hours, peaks at 24 hours, normalizes within 5 days.
    • Useful in diagnosing conditions such as acute hepatocellular disorders, pulmonary embolism, congestive heart failure, and muscular dystrophy.
    • Elevation noted in conditions like viral hepatitis (100x ULN) and liver cirrhosis (4x ULN).

    Alanine Aminotransferase (ALT)

    • Function: Transfers amino groups between alanine and alpha-keto acids, resulting in glutamate and pyruvate formation.
    • Former names: Serum glutamic-pyruvic transaminase (SGPT or GPT).
    • Cofactor: Pyridoxal phosphate (Vitamin B6).
    • ALT elevation is primarily associated with hepatic disorders and is often higher than AST due to a longer half-life (47 hours vs. 17 hours).
    • In acute hepatocellular injury, typically, ALT rises beyond AST within 24-48 hours.

    Phosphatases Overview

    • Include Alkaline Phosphatase (ALP) and Acid Phosphatase (ACP), which catalyze hydrolysis of phosphomonoesters yielding inorganic phosphate.

    Alkaline Phosphatase (ALP)

    • E.C. number: 3.1.3.1.
    • Optimum pH: 9.0 - 10.0; requires magnesium and zinc as cofactors.
    • Major tissue sources: liver, bone, intestine, spleen, and kidney.
    • Four major isoenzymes based on origin: placental, liver, bone, intestinal.

    Diagnostic Significance of ALP

    • Elevated in hepatobiliary disorders (e.g., biliary tract obstruction, hepatitis).
    • May indicate bone disorders like Paget's disease, osteomalacia, and hyperparathyroidism.
    • Normal pregnancy can result in increased ALP levels detectable from weeks 16 to 20.

    Acid Phosphatase (ACP)

    • Includes isoenzymes specific to prostatic and red blood cell sources.
    • Prostatic ACP inhibited by tartrate; red cell ACP inhibited by formaldehyde.
    • TRAP (Tartrate Resistant Acid Phosphatase) serves as a marker for hairy cell leukemia.

    Diagnostic Significance of ACP

    • Utilized in the detection of prostatic carcinoma; less specific than prostate-specific antigen.
    • Important for forensic investigations, with seminal fluid ACP potentially indicating rape.

    Cholestasis

    • Represents failure of bile excretion; can be extrahepatic (e.g., gallstones) or intrahepatic (e.g., viral hepatitis).
    • Associated with cholangitis and characterized by Charcot's triad and Reynolds' pentad symptoms.

    Summary of Diagnostic Significance

    • Increased ALP is linked to hepatobiliary and bone disorders.
    • Decreased ALP indicates conditions such as hypophosphatasia.
    • Differentiate ALP isoenzymes through heat stability and chemical inhibition tests.

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    Description

    This quiz covers the critical liver enzymes AST and ALT, their functions, sources, and diagnostic significance. Explore the roles they play in amino acid metabolism and their relevance in various medical conditions.

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