Questions and Answers
What is the approximate number of people worldwide who are G6PD deficient?
Which of the following is NOT a source of blood glucose in a normal person?
What is the role of glucose in the liver during glycogen synthesis?
What is the byproduct of the pentose phosphate pathway?
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Why is gluconeogenesis not simply the reversal of glycolysis?
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What is the trigger for haemolytic anaemia in people with G6PD deficiency?
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What is the source of blood glucose in conditions of carbohydrate deprivation?
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Which of the following is a glucogenic amino acid?
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What is the effect of insulin on glycogen synthesis in the liver?
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What is the effect of glucagon on plasma amino acids?
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What is the primary source of energy for the brain?
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What is the effect of insulin on glucose uptake in muscle?
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What is the primary fate of glucose in the liver during the fed state?
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What is the effect of glucagon on fatty acid metabolism in the liver?
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What is the characteristic of a glucose tolerance curve in diabetes type 2?
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What is the primary metabolic pathway in erythrocytes?
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What is the primary function of glucose in the body?
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What is the normal physiological circulating glucose concentration in the blood?
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What is the consequence of glucose concentration dropping to 2.5 or less?
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What is the role of glucose in the production of fatty acids and steroids?
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What is the advantage of glucose as a metabolic fuel?
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What is the primary pathway involving glucose in skeletal muscle?
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What is the function of glucose in adipose tissue?
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What is the consequence of glucose-6-phosphate dehydrogenase deficiency?
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What is the role of the liver in glucose metabolism?
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What is the result of high glucose concentrations in the blood?
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What is the primary function of insulin in the body?
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Which enzyme is responsible for the conversion of pyruvate to PEP in gluconeogenesis?
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What is the primary function of glucagon in the body?
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Which of the following reactions is reversible in glycolysis?
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What is the primary source of substrate for gluconeogenesis during fasting?
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Which of the following hormones plays a crucial role in maintaining physiological blood glucose concentrations?
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Study Notes
Glucose Metabolism and the Liver
- Glucose is a vital metabolic fuel, essential for the body's functioning.
- The liver plays a crucial role in maintaining blood glucose homeostasis.
- Glucose is the preferred fuel source for all tissues, with some tissues having a continuous dependence on glucose.
Blood Glucose Concentration
- The normal physiological circulating glucose concentration is 3.9-6.2 mM.
- Average fasting blood glucose concentration is 4.4-5 mM for most adults.
- If blood glucose concentration drops to 2.5 or less, coma and death can result.
- If it rises for an extended period, dehydration, wasting of body tissue, and eventually death will result.
Roles of Glucose
- Glucose is a source of energy, generating 2 ATP through glycolysis and 31 ATP through oxidative phosphorylation.
- It is a source of NADPH, necessary for synthetic reactions, fatty acid synthesis, and drug metabolism.
- Glucose is a source of pentose sugars for synthetic reactions, such as nucleotide and DNA synthesis.
- It is a source of carbon for other sugars and glycoconjugates.
Advantages and Disadvantages of Glucose as a Metabolic Fuel
- Advantages: water-soluble, no carrier required in circulation, can cross the blood-brain barrier, and can be oxidized anaerobically.
- Disadvantages: relatively low yield of ATP/mole compared to fatty acids, osmotically active, and can cause direct cellular damage or accumulate toxic by-products in high concentrations.
Pathways Involving Glucose
- Predominant pathways involving glucose differ in various tissues.
- The liver can provide glucose for other tissues.
- Glucose is used in glycolysis, glycogen synthesis, and the pentose phosphate pathway in different tissues.
Role of Glucose in Different Tissues
- Skeletal muscle: glycolysis for anaerobic muscle contraction, glycolysis/TCA cycle for energy, and glycogen synthesis/degradation for energy storage.
- Heart/brain: glycolysis/TCA cycle for energy.
- Adipose tissue: glycolysis for production of glycerol phosphate for TAG synthesis.
- Erythrocyte: glycolysis for energy, pentose phosphate pathway for NADPH synthesis.
Glucose-6-Phosphate Dehydrogenase Deficiency
- X-linked hereditary disorder, affecting more than 400 million people worldwide.
- Triggers for hemolytic anemia in people with G6PD deficiency include favism, resulting from the ingestion of fava beans.
Gluconeogenesis
- Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources in the liver.
- Sources: lactate, glycerol, other monosaccharides, and glucogenic amino acids (all except leu and lys).
- Not from fatty acids.
- Gluconeogenesis is not simply the reversal of glycolysis, with three irreversible reactions in glycolysis that must be bypassed.
Regulation of Gluconeogenesis
- Mobilization of substrate: glycerol from fat breakdown, amino acids from muscle protein breakdown.
- Activation of enzymes: G6Pase, F1,6bisPase, PEPCK, and pyruvate carboxylase.
- Regulation by insulin, glucagon, and adrenaline.
Blood Glucose Maintenance
- Insulin, glucagon, and adrenaline signal and coordinate the activities of the liver, adipose tissue, and muscle tissue to maintain physiological blood glucose concentrations.
- Insulin promotes synthesis and storage, while glucagon promotes degradation of stored fuel.
Insulin and Glucagon
- Insulin: anabolic hormone, promoting synthesis and storage.
- Glucagon: catabolic hormone, promoting degradation of stored fuel.
- Sites of insulin action: liver, adipose tissue, and muscle.
- Metabolic effects of insulin: inhibition of gluconeogenesis, activation of glycogen synthesis, increased fatty acid synthesis, and increased amino acid uptake and protein synthesis.
Metabolic Effects of Glucagon
- Increase in blood glucose: increase in glycogenolysis and gluconeogenesis in the liver.
- Increase in circulating fatty acids and ketone bodies: increase in adipose tissue lipolysis, fatty acid oxidation in the liver, and ketone body formation.
- Decrease in plasma amino acids: increase in uptake by the liver for gluconeogenesis.
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Description
This quiz covers the liver's role in glucose metabolism, including gluconeogenesis, glucose sources, and blood glucose homeostasis. It's a comprehensive test for MBBS Stage 1 students.