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Questions and Answers
What condition is associated with an ALT elevation higher than AST due to its longer half-life?
Which isoenzyme of alkaline phosphatase is predominantly found in the prostate?
What is the optimum pH range for alkaline phosphatase activity?
What method is NOT commonly used to differentiate the isoenzymes of alkaline phosphatase?
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In what situation is AST usually greater than ALT in acute hepatocellular injury?
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Which tissue does NOT primarily source alkaline phosphatase activity?
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Which statement regarding the De Ritis ratio is correct?
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Which cofactor is essential for the activity of both alkaline and acid phosphatases?
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What is the primary function of Aspartate Aminotransferase (AST)?
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Which tissue has the highest source of Alanine Aminotransferase (ALT)?
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What cofactor is used by both AST and ALT enzymes?
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During an Acute Myocardial Infarction (AMI), how long does it typically take for AST levels to peak?
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Which of the following statements about AST isoenzyme fractions is true?
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For which condition is AST diagnostic significance are limited?
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Which tissue is NOT a source of Aspartate Aminotransferase (AST)?
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Which of the following best describes the role of ketoacids formed by AST?
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What condition typically leads to an increased synthesis of alkaline phosphatase (ALP)?
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Which of the following is NOT a potential cause of extrahepatic cholestasis?
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Which triad is associated with cholangitis?
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What condition is indicated by an increase in alkaline phosphatase during normal pregnancy?
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Which enzyme is primarily used as a marker for hairy cell leukemia?
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In which scenario would acid phosphatase activity be particularly useful?
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Which alkaline phosphatase isoenzyme is primarily associated with hepatobiliary conditions?
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What is the impact of hypophosphatasia on alkaline phosphatase levels?
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Which factor is likely to elevate acid phosphatase activity in vaginal washings?
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What indicates bone ALP activity after heating serum at 56 degrees Celsius for 10 minutes?
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Which agent inhibits intestinal ALP and placental ALP more effectively than liver and bone ALP?
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Which isoenzyme is most heat stable, resisting denaturation at 65 degrees Celsius for 30 minutes?
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Which alkaline phosphatase isoenzyme is associated with metastatic carcinoma of pleural surfaces?
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What is the distinguishing feature of placental ALP compared to other isoenzymes in terms of heat stability?
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Which of the following factors indicates the presence of hepatobiliary disorders based on alkaline phosphatase levels?
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Which factor is used to differentiate alkaline phosphatase isoenzymes through chemical inhibition?
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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.
