Liver Functions and Metabolism Quiz
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Questions and Answers

What is primarily responsible for the manifestations in certain porphyrias?

  • Oxidation of uroporphorinigen
  • Decreased heme levels
  • Accumulation of ALA and PBG (correct)
  • Deficiency in uroporphorinigen decarboxylase

    • What symptom is associated with the accumulation of oxidized uroporphorinigen?

  • Abdominal pain
  • Seizures
  • Skin blistering (correct)
  • Vomiting

    • Which treatment is appropriate for managing the symptoms of ALA and PBG accumulation?

  • Intravenous iron supplements
  • Haematin (correct)
  • Chloroquine
  • Sunblock lotion

    • What triggers the symptoms of Porphyria Cutanea Tarda (PCT)?

    <p>Exposure to sunlight</p> Signup and view all the answers

    What diagnostic measure is key for identifying elevated levels in patients with certain porphyrias?

    <p>Urinary levels of ALA and PBG</p> Signup and view all the answers

    What is the primary function of gluconeogenesis in the liver?

    <p>To maintain blood glucose levels when glycogen stores are low</p> Signup and view all the answers

    Which of the following is NOT a product synthesized by the liver?

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

    Which process is primarily involved in the conversion of amino acids to glucose in the liver?

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

    What is the primary role of albumin in the blood?

    <p>Transporting fats and other substances</p> Signup and view all the answers

    What role does the liver play in protein metabolism?

    <p>Converting ammonia into urea</p> Signup and view all the answers

    During which process does the liver convert stored glycogen into glucose?

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

    Which vitamin is converted to its active form in the kidneys after being processed in the liver?

    <p>Vitamin D</p> Signup and view all the answers

    Which statement best describes the liver's function in lipid metabolism?

    <p>The liver oxidizes triglycerides to produce energy</p> Signup and view all the answers

    What is a critical function of the liver related to ammonia?

    <p>Synthesis of urea</p> Signup and view all the answers

    Which type of proteins synthesized in the liver mainly regulate blood coagulation?

    <p>Clotting factors</p> Signup and view all the answers

    What is the role of cholesterol in the liver's biosynthetic functions?

    <p>It serves as a building block for steroid hormones</p> Signup and view all the answers

    Which metabolic products are synthesized by the liver?

    <p>Lipids, glucose, and plasma proteins</p> Signup and view all the answers

    How does the liver assist in maintaining energy balance during fasting?

    <p>By performing gluconeogenesis from non-carbohydrate sources</p> Signup and view all the answers

    What are porphyrias, as related to liver function?

    <p>Conditions resulting from defects in haem biosynthesis</p> Signup and view all the answers

    What is the role of non-essential amino acids synthesized in the liver?

    <p>They serve as building blocks for proteins</p> Signup and view all the answers

    What is the most abundant plasma protein found in serum?

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

    What is the primary function of haem in the body?

    <p>Oxygen binding and transport</p> Signup and view all the answers

    Which step in haem synthesis occurs in the mitochondria?

    <p>Synthesis of Aminolevulinic Acid</p> Signup and view all the answers

    Which enzyme acts on Aminolevulinic Acid (ALA) to produce porphobilinogen (PBG)?

    <p>ALA dehydratase</p> Signup and view all the answers

    What is the final compound produced in the synthesis of haem after iron chelation?

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

    Which process is not facilitated by haem?

    <p>DNA replication</p> Signup and view all the answers

    What is produced immediately after hydroxymethylbilane in the haem synthesis pathway?

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

    What is the role of ferrochelatase in haem synthesis?

    <p>Chelates iron to protoporphyrin</p> Signup and view all the answers

    Which of the following is NOT a location where haem is synthesized?

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

    What is the result of ALA dehydratase and ferrochelatase inhibition?

    <p>Microcytic anemia</p> Signup and view all the answers

    Which of the following therapies is NOT used for treating the conditions related to porphyrins?

    <p>Administration of heme</p> Signup and view all the answers

    What triggers attacks in Acute Intermittent Porphyria (AIP)?

    <p>Drugs inducing cytochrome P450 expression</p> Signup and view all the answers

    What is a characteristic symptom of porphyrias?

    <p>Red/purple urine</p> Signup and view all the answers

    Which Porphyria is associated with a defect in porphobilinogen deaminase?

    <p>Acute Intermittent Porphyria</p> Signup and view all the answers

    Which external factor can trigger porphyrin accumulation?

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

    What is an important metabolic consequence of decreased heme production in porphyrias?

    <p>Accumulation of heme pathway intermediates</p> Signup and view all the answers

    Which symptom is NOT commonly associated with acute porphyric attacks?

    <p>Rapid weight gain</p> Signup and view all the answers

    What process occurs due to decreased heme that exacerbates the accumulation of ALA and PBG?

    <p>Loss of negative feedback</p> Signup and view all the answers

    Which symptom directly correlates with the skin's reaction to oxidized uroporphorinigen?

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

    What is a common diagnostic measure for confirming Porphyria Cutanea Tarda?

    <p>Urinary uroporphorinigen measurement</p> Signup and view all the answers

    Which treatment promotes the urinary excretion of uroporphorinigen effectively?

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

    What is a key lifestyle recommendation for managing symptoms associated with Porphyria Cutanea Tarda?

    <p>Limit exposure to excess sunlight</p> Signup and view all the answers

    Which molecule is produced first in the synthesis of haem from glycine and succinyl Co-A?

    <p>Aminolevulinic Acid (ALA)</p> Signup and view all the answers

    What is the final step in the synthesis of haem after protoporphyrin is formed?

    <p>Chelation of iron by ferrochelatase</p> Signup and view all the answers

    Which of the following processes involves haem as a cofactor?

    <p>Electron transport</p> Signup and view all the answers

    Which enzyme is responsible for the conversion of ALA to PBG in the synthesis of haem?

    <p>ALA dehydratase</p> Signup and view all the answers

    Where does the conversion of Coproporphyrinogen to protoporphyrin occur?

    <p>In the mitochondria</p> Signup and view all the answers

    What is the function of peroxidases in which haem is involved?

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

    Which compound is generated after hydroxymethylbilane during haem synthesis?

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

    What type of pigment is haem classified as, and what is its primary characteristic?

    <p>A red organic pigment that binds oxygen</p> Signup and view all the answers

    What condition results from a significant decrease in albumin levels in the blood?

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

    What primarily regulates the rate of albumin synthesis?

    <p>Colloid pressure</p> Signup and view all the answers

    Which of the following is least likely to be caused by hypoalbuminemia?

    <p>Increased albumin excretion in urine</p> Signup and view all the answers

    What is the primary process by which albumin is synthesized within the liver cells?

    <p>Post-translational modification in the Golgi</p> Signup and view all the answers

    What type of plasma protein exerts oncotic pressure and is involved in immune function?

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

    Which combination of factors can lead to hypoalbuminemia?

    <p>Impaired liver synthesis and chronic kidney disease</p> Signup and view all the answers

    Which statement about globulins is accurate?

    <p>They include immunoglobulins which function in the immune response.</p> Signup and view all the answers

    What is a potential effect of increased renal excretion of albumin in chronic kidney disease?

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

    What mechanism is responsible for pulling fluid from the interstitium into the blood?

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

    What is a common consequence of fluid retention due to hypoalbuminemia?

    <p>Peripheral edema</p> Signup and view all the answers

    What is the immediate product formed after the action of UPG Synthase on hydroxymethylbilane?

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

    Which enzyme is responsible for converting coproporphyrinogen into protoporphyrin?

    <p>UPG Decarboxylase</p> Signup and view all the answers

    How does haem regulate haem synthesis in the body?

    <p>By inhibiting ALA Synthase expression and activity</p> Signup and view all the answers

    What is a notable consequence of lead poisoning in terms of haem synthesis?

    <p>Accumulative defects leading to acute porphyrias</p> Signup and view all the answers

    Which substance is directly chelated with iron to produce haem?

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

    What common symptom is associated with lead poisoning?

    <p>Abdominal pain and irritability</p> Signup and view all the answers

    Which of the following statements best describes the dual regulation of haemoglobin production?

    <p>A balance between haem inhibition of ALA Synthase and stimulation of globin synthesis is crucial</p> Signup and view all the answers

    What metabolic consequence arises from impaired enzyme activity in the context of lead poisoning?

    <p>Diversion to alternate products and substrate deficiency</p> Signup and view all the answers

    Which enzyme defect is responsible for Acute Intermittent Porphyria (AIP)?

    <p>Porphobilinogen deaminase</p> Signup and view all the answers

    What is a characteristic feature of porphyrias related to urine?

    <p>It becomes red or purple</p> Signup and view all the answers

    Which trigger is known to induce symptoms of Acute Intermittent Porphyria?

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

    What is the typical result of inhibiting ALA dehydratase and ferrochelatase?

    <p>Microcytic anemia due to lack of hemoglobin</p> Signup and view all the answers

    Which of the following therapies is specifically indicated for managing porphyrin accumulation?

    <p>Chelation therapy</p> Signup and view all the answers

    What may cause the production of porphyrins in porphyrias?

    <p>Elevated cytochrome P450 expression</p> Signup and view all the answers

    Which symptom is commonly associated with porphyria attacks?

    <p>Abdominal pain</p> Signup and view all the answers

    Which of the following types of porphyria is hereditary?

    <p>All of the above</p> Signup and view all the answers

    Study Notes

    Liver Functions

    • The liver is a vital organ with diverse functions including:
      • Metabolism of carbohydrates, fats, and proteins
      • Synthesis of essential compounds
      • Excretion and detoxification

    Carbohydrate Metabolism

    • The liver maintains blood glucose levels through:
      • Glycogenesis: Synthesis of glycogen from glucose when blood glucose levels are high.
      • Glycogenolysis: Breakdown of glycogen into glucose when blood glucose levels are low.
      • Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources like glycerol, lactate, and amino acids during prolonged fasting.

    Lipid Metabolism

    • The liver plays a crucial role in lipid metabolism:
      • Oxidation of triglycerides: Produces energy.
      • Ketone body synthesis: Converts fatty acids to ketone bodies which can be used as energy by other tissues.
      • Triglyceride synthesis: Converts excess carbohydrates and proteins into fatty acids and triglycerides.
      • Cholesterol and phospholipid synthesis: Produces cholesterol and phospholipids needed for cell membranes and other functions.
      • Lipoprotein synthesis: Synthesizes very-low-density lipoproteins (VLDLs) to transport triglycerides, cholesterol, and phospholipids to other tissues.

    Protein Metabolism

    • The liver is essential for protein metabolism:
      • Deamination and transamination: Breakdown of amino acids for energy or conversion to glucose or lipids.
      • Urea synthesis: Removal of ammonia, a toxic byproduct of protein metabolism.
      • Non-essential amino acid synthesis: Produces non-essential amino acids like glutamine.
      • Plasma protein synthesis: Synthesizes most of the plasma proteins including albumin, globulins, and clotting factors.

    Vitamin Metabolism

    • The liver is involved in the metabolism of Vitamin D:
      • 25-hydroxylation: Converts the precursor form of Vitamin D (cholecalciferol) to its circulating form (25-hydroxy-Vitamin D).

    Biosynthetic Products of the Liver

    • The liver synthesizes a wide range of essential compounds including:
      • Nutrients: Triglycerides, cholesterol, phospholipids, lipoproteins, glycogen, glucose, and non-essential amino acids.
      • Plasma proteins: Albumin, globulins, clotting factors (e.g., fibrinogen).
      • Haem: Iron-containing molecule crucial for oxygen transport, storage, and metabolism.
      • Bile acids: Aid in fat digestion and absorption.
      • Nucleotide precursors: Building blocks for DNA and RNA.
      • Urea: Waste product of protein metabolism.

    Plasma Proteins Synthesized by the Liver

    • The liver produces a variety of plasma proteins with diverse functions:
      • Carrier proteins: Bind and transport fat-soluble nutrients, hormones, drugs, and ions (e.g., albumin, globulins).
      • Clotting/Anticlotting factors: Regulate blood coagulation (e.g., fibronectin, components of the complement cascade).
      • Hormones: Regulate metabolism and growth (e.g., fibroblast growth factor, insulin-like growth factor).
      • Apolipoproteins: Enable transport of lipids in the blood.

    Albumin

    • Albumin is the most abundant protein in the blood:
      • Synthesis: Produced exclusively by hepatic cells.
      • Physiological role:
        • Acts as a carrier protein for many substances including fatty acids, hormones, drugs, and ions.
        • Contributes to maintaining osmotic pressure in the blood.

    Haem Synthesis

    • Haem is essential for the function of many proteins involved in oxygen transport, storage, and metabolism:
      • Synthesis: Occurs in the liver, muscle, and bone marrow.
      • Process:
        • Starts in the mitochondria with the synthesis of aminolevulinic acid (ALA).
        • Proceeds through a sequence of steps involving various enzymes culminating in the formation of haem.
    • Defects in haem synthesis:
      • Can lead to porphyrias, a group of inherited disorders characterized by the accumulation of porphyrins in the body.

    Porphyrias

    • Porphyrias are a group of genetic disorders affecting the haem synthesis pathway:
      • Causes: Mutations in enzymes involved in haem synthesis leading to a buildup of porphyrin precursors.
      • Symptoms: Vary depending on the deficient enzyme, ranging from mild skin sensitivity to severe abdominal pain, neurological dysfunction, and psychiatric problems.
      • Diagnosis: Based on measuring porphyrins in urine and blood.
      • Treatment: Focuses on managing symptoms and avoiding triggers that exacerbate the condition.

    Acute Intermittent Porphyria (AIP)

    • AIP is a type of porphyria caused by a deficiency in the enzyme hydroxymethylbilane synthase (also known as porphobilinogen deaminase):
      • Causes: Accumulation of porphyrin precursors δ-aminolevulinate (ALA) and porphobilinogen (PBG).
      • Triggers: Drugs that induce cytochrome P450 enzymes, including barbiturates and progestins.
      • Symptoms: Severe abdominal pain, nausea, vomiting, neurological dysfunction, seizures, and psychosis.
      • Diagnosis: Elevated levels of ALA and PBG in the urine.
      • Treatment: Haematin, a synthetic form of haem, helps to inhibit ALA synthase and reduce the production of ALA and PBG.

    Porphyria Cutanea Tarda (PCT)

    • PCT is a type of porphyria caused by a deficiency in the enzyme uroporphyrinogen decarboxylase:
      • Causes: Accumulation of uroporphyrinogen, a photosensitive porphyrin that causes skin damage.
      • Triggers: Sunlight exposure, alcohol consumption, and iron deficiency.
      • Symptoms: Skin blistering, photosensitivity, hyperpigmentation, and increased hair growth.
      • Diagnosis: Elevated levels of uroporphyrinogen in urine and blood.
      • Treatment: Avoidance of sunlight, alcohol, and iron supplements. Anti-malarials like chloroquine can be used to bind uroporphyrinogen and increase its urinary excretion.

    Albumin

    • Albumin is the most abundant protein in the blood plasma
    • It is synthesized by the liver and is essential in regulating fluid balance
    • Albumin contributes 75-80% of the oncotic pressure in the blood which pulls fluid from the interstitial spaces into the blood vessels
    • Hypoalbuminemia, a decrease in albumin levels in the blood, can be caused by impaired hepatic synthesis due to conditions like liver cirrhosis or increased renal excretion due to conditions like nephrotic syndrome
    • Hypoalbuminemia leads to decreased plasma oncotic pressure, resulting in edema and ascites

    Haem Synthesis by Liver Cells

    • Haem is a chemical containing iron chelated in a porphyrin ring
    • Haem is synthesized in the liver, muscles, and bone marrow
    • Haem functions as a cofactor for hemoproteins which are involved in a range of processes, including oxygen transport, storage, and metabolism
    • Haem synthesis is initiated in mitochondria where glycine and succinyl Co-A are converted into aminolevulinic acid (ALA) by the enzyme ALA synthase
    • ALA is shuttled into the cytoplasm and converted into porphobilinogen (PBG) by ALA dehydratase, followed by a conversion to hydroxymethylbilane by PBG deaminase
    • Hydroxymethylbilane is converted to uroporphyrinogen, then coproporphyrinogen by sequential enzyme actions
    • The coproporphyrinogen is re-entered into the mitochondria to form protoporphyrin
    • Protoporphyrin is then chelated to iron by the enzyme ferrochelatase to produce haem

    Regulation of Haem Synthesis

    • Haem levels are the primary factor regulating the rate of haem synthesis
    • Haem inhibits both activity and expression of the enzyme ALA synthase in hepatocytes
    • Haem also stimulates globin synthesis to maintain low levels of free haem

    Defects in Haem Synthesis

    • Lead poisoning: Leads to inhibition of ALA dehydratase and ferrochelatase, resulting in a reduction of haem production and increased ALA levels
    • Porphyrias: A group of liver disorders due to mutations in enzymes involved in haem synthesis, leading to an accumulation of porphyrins in the body and resulting in red/purple urine

    Lead Poisoning

    • Exposure to lead can occur through old paint, dust, batteries, and industrial settings
    • Symptoms include anemia, constipation, abdominal pain, irritability, seizures, and coma
    • Lead poisoning can be treated by removing the source of lead exposure and using chelation therapy with succimer or EDTA

    Porphyrias

    • Can be hereditary and caused by mutations in haem synthesis enzymes
    • Characterized by increased urinary porphyrin excretion
    • Symptoms include abdominal pain, vomiting, confusion, fever, constipation, increased blood pressure, and seizures
    • Two examples of porphyrias are Acute Intermittent Porphyria (AIP) and Porphyria Cutanea Tarda (PCT)

    Acute Intermittent Porphyria (AIP)

    • Due to a deficiency in porphobilinogen deaminase (uroporphyrinogen synthase I)
    • Attacks are often triggered by drugs, stress, hormones, and fasting
    • Symptoms include seizures, psychosis, severe abdominal pain, nausea, vomiting, and coma
    • Diagnosis is made by measuring urinary ALA and PBG levels
    • Treatment involves using haematin to restore the inhibition of ALA synthase

    Porphyria Cutanea Tarda (PCT)

    • Results from a deficiency in uropoprhorinigen decarboxylase
    • Leads to a build-up of uroporphorinigen and a decrease in haem production
    • UPO accumulates in the skin and becomes photoreactive, causing cell damage, inflammation, blistering, and skin discolouration upon sun exposure
    • Symptoms include swelling, itching, and blistering of the skin
    • Patients need to avoid sunlight, alcohol, and iron supplements
    • Treatment utilizes anti-malarials like chloroquine to bind UPO and enhance urinary excretion.

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