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Questions and Answers
What is the primary role of lipids stored in adipose tissue during extended fasting?
What is the primary role of lipids stored in adipose tissue during extended fasting?
Which physiological response is primarily enhanced by the release of adrenaline?
Which physiological response is primarily enhanced by the release of adrenaline?
What is the significance of lipids as a fuel source compared to proteins?
What is the significance of lipids as a fuel source compared to proteins?
How long can lipid stores in adipose tissue potentially sustain life during energy deficits?
How long can lipid stores in adipose tissue potentially sustain life during energy deficits?
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In what way do proteins differ from lipids in terms of energy utilization?
In what way do proteins differ from lipids in terms of energy utilization?
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What is one of the main functions of insulin in relation to muscle tissue?
What is one of the main functions of insulin in relation to muscle tissue?
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During the post-absorptive state, what is the primary source of glucose in the body?
During the post-absorptive state, what is the primary source of glucose in the body?
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What occurs during the initial phase (12-48 hours) after a meal when glycogen stores begin to deplete?
What occurs during the initial phase (12-48 hours) after a meal when glycogen stores begin to deplete?
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Which hormone is primarily responsible for glycogenolysis in response to low blood glucose levels?
Which hormone is primarily responsible for glycogenolysis in response to low blood glucose levels?
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What is the primary metabolic state referred to as the 'anabolic' phase after meals?
What is the primary metabolic state referred to as the 'anabolic' phase after meals?
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What is the primary energy source used by skeletal muscle during heavy exercise?
What is the primary energy source used by skeletal muscle during heavy exercise?
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What process occurs when muscle glycogen is depleted during exercise?
What process occurs when muscle glycogen is depleted during exercise?
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During prolonged exercise, which metabolic process becomes predominant in muscle cells?
During prolonged exercise, which metabolic process becomes predominant in muscle cells?
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Which of the following provides ATP without the need for oxygen?
Which of the following provides ATP without the need for oxygen?
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What happens to ATP production after initial phosphocreatine depletion during exercise?
What happens to ATP production after initial phosphocreatine depletion during exercise?
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Which fuel sources may muscles utilize after depleting glycogen during prolonged exercise?
Which fuel sources may muscles utilize after depleting glycogen during prolonged exercise?
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During heavy exercise, how does muscle metabolism initially adapt?
During heavy exercise, how does muscle metabolism initially adapt?
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In the context of muscle energy metabolism, what is a common misconception about the role of ketone bodies?
In the context of muscle energy metabolism, what is a common misconception about the role of ketone bodies?
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What is the role of hormone-sensitive lipase during increased energy demand?
What is the role of hormone-sensitive lipase during increased energy demand?
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Which substrates are primarily used by the liver and kidneys for gluconeogenesis?
Which substrates are primarily used by the liver and kidneys for gluconeogenesis?
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How does glucagon affect liver glycogenolysis?
How does glucagon affect liver glycogenolysis?
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What is the main consequence of the adipose tissue's insulin dependency?
What is the main consequence of the adipose tissue's insulin dependency?
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During the gluconeogenic phase, what happens after 2-3 days without carbohydrate intake?
During the gluconeogenic phase, what happens after 2-3 days without carbohydrate intake?
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What is the primary function of released fatty acids in peripheral tissues?
What is the primary function of released fatty acids in peripheral tissues?
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Which organ primarily responds to glucagon by increasing glycogenolysis?
Which organ primarily responds to glucagon by increasing glycogenolysis?
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What does the breakdown of triglycerides produce that can be used for energy?
What does the breakdown of triglycerides produce that can be used for energy?
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What process becomes the primary method of energy production in the brain during prolonged fasting?
What process becomes the primary method of energy production in the brain during prolonged fasting?
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Which of the following states predominantly involves the mobilization of fat for energy?
Which of the following states predominantly involves the mobilization of fat for energy?
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What occurs to muscle proteins during prolonged fasting?
What occurs to muscle proteins during prolonged fasting?
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What is the initial source of glucose production during the fasting state?
What is the initial source of glucose production during the fasting state?
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Why can't fatty acids be utilized as energy by the brain?
Why can't fatty acids be utilized as energy by the brain?
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During prolonged fasting, which metabolic process is decreased in the liver?
During prolonged fasting, which metabolic process is decreased in the liver?
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What is the primary advantage of fasting for the body?
What is the primary advantage of fasting for the body?
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Which energy source does the brain primarily utilize under normal conditions?
Which energy source does the brain primarily utilize under normal conditions?
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What is the role of ketone bodies during fasting?
What is the role of ketone bodies during fasting?
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What is the primary function of adrenaline in response to low blood glucose levels?
What is the primary function of adrenaline in response to low blood glucose levels?
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How long can free glucose in the blood sustain the brain's energy needs?
How long can free glucose in the blood sustain the brain's energy needs?
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What roles do hepatic glycogen stores play in energy supply under resting conditions?
What roles do hepatic glycogen stores play in energy supply under resting conditions?
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Which process is stimulated by adrenaline to increase the availability of fatty acids?
Which process is stimulated by adrenaline to increase the availability of fatty acids?
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What effect does stress or low glucose have on energy mobilization?
What effect does stress or low glucose have on energy mobilization?
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What type of hormone is adrenaline classified as, based on its function?
What type of hormone is adrenaline classified as, based on its function?
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What is the source of glucose during periods of stress or low blood sugar as described?
What is the source of glucose during periods of stress or low blood sugar as described?
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What is the total amount of free glucose typically found in the blood and extracellular fluid?
What is the total amount of free glucose typically found in the blood and extracellular fluid?
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Study Notes
Metabolic Integration During Fasting
- Fasting triggers a cascade of metabolic adjustments across various organs to maintain energy balance.
- Initial fasting relies on glycogenolysis (liver glycogen breakdown), while prolonged fasting necessitates gluconeogenesis (glucose production from non-carbohydrate sources like amino acids and glycerol).
- Fatty acid oxidation becomes crucial, providing energy, and ketone bodies become an important fuel source, especially for the brain.
- The liver plays a central role in glucose homeostasis during fasting, driving glycogenolysis and gluconeogenesis to keep blood glucose levels stable.
- During prolonged fasting, the body transitions towards using fatty acids and ketone bodies for fuel to preserve glucose stores for the brain and other vital organs.
- Muscle protein breakdown supports gluconeogenesis, providing amino acids for glucose synthesis.
- Reduced metabolic rate, a consequence of decreased thyroid hormone (T3) levels, helps conserve energy reserves in prolonged fasting.
Role of Hormones During Fasting
- Insulin: An anabolic hormone stimulating glucose uptake, glycogen synthesis, and lipid storage. Low insulin levels during fasting are crucial for mobilizing energy stores.
- Glucagon: A catabolic hormone promoting glycogenolysis and gluconeogenesis to maintain blood glucose levels.
- Adrenaline (epinephrine): A rapid-response hormone increasing blood glucose via glycogenolysis and lipolysis, especially during stress or low blood glucose.
- Cortisol: A long-term stress hormone affecting metabolism by increasing glycogenolysis, lipolysis, inhibiting peripheral glucose utilization, and stimulating gluconeogenesis and protein breakdown, which is important in adapting to prolonged fasting. The long term effects of excess cortisol can have detrimental impacts including hyperglycemia, insulin resistance and fat redistribution
Organ-Specific Adaptations
- Liver: Central to glucose homeostasis, it performs glycogenolysis and gluconeogenesis. It produces ketone bodies from fatty acids for energy during fasting.
- Adipose tissue: Releases fatty acids into the bloodstream for energy utilization by other tissues during fasting.
- Skeletal Muscle: Initially uses stored glycogen and then shifts to fatty acids and ketone bodies, preserving muscle protein for vital functions during prolonged fasting.
- Brain: Primarily relies on glucose, but adapts to use ketone bodies during prolonged fasting.
- Kidney: Supports gluconeogenesis during fasting, helping to maintain blood glucose levels.
Metabolic States
- Post-prandial (fed): High insulin levels promote glucose uptake and energy storage (glycogen and triglycerides).
- Fasting: Glycogen breakdown and gluconeogenesis are prioritized to maintain blood glucose levels.
- Starvation: A prolonged fasting state, where the body adapts to utilizing fatty acids and ketone bodies extensively as primary fuel sources.
Energy Sources During Fasting
- Carbohydrates: Limited storage, primarily glycogen. Liver glycogen is first used, followed by gluconeogenesis.
- Lipids: Adipose tissue triglycerides provide a major source of energy during extended fasting.
- Proteins: Breakdown of muscle proteins contributes to gluconeogenesis during prolonged fasting.
Brain Fuel Adaptation
- Glucose: Primary energy source in the fed state and for a limited time during fasting.
- Ketone bodies: Crucial alternative fuel source for the brain during prolonged fasting to prevent glucose depletion.
Physical Exercise (Anaerobic and Aerobic):
- Anaerobic Exercise: Muscles initially utilize phosphocreatine and ATP stores to regenerate ATP; glycogen breakdown to lactate later.
- Aerobic Exercise: Muscle cells rely mostly on aerobic metabolism, utilizing fatty acids (or ketone bodies during extended fasting/glycogen depletion) for energy.
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Description
This quiz explores the metabolic adaptations that occur during fasting. It covers the roles of various organs, the transition from glycogenolysis to gluconeogenesis, and the importance of fatty acid oxidation and ketone bodies. Understand how the liver maintains glucose homeostasis and how muscle protein breakdown contributes to energy balance.
