Energy, metabolism and exercise Flashcards
What are the three states of metabolism in relation to feeding?
The three states are the fed state, post-absorptive state, and starvation state.
What are the key metabolic changes that occur from the absorptive state to the post-absorptive state?
The key metabolic changes include a shift from glucose utilization to glycogen breakdown, triglyceride synthesis to fatty acid oxidation, and amino acid uptake to protein breakdown.
Which energy source is predominant in most cells during the absorptive state?
Glucose is the primary energy source for most cells during the absorptive state
Which energy source becomes dominant in most cells during the post-absorptive state?
Triglycerides become the primary energy source for most cells during the post-absorptive state.
What is the molar ratio of insulin to glucagon in the blood during the fed state?
The fed state is characterized by a high insulin and low glucagon ratio.
What is the molar ratio of insulin to glucagon in the blood during the fasting state?
The fasting state is characterized by a low insulin and high glucagon ratio.
When does prolonged fasting or starvation occur?
Prolonged fasting or starvation occurs when the fasting state lasts for more than 12 hours.
What is the ratio of insulin to glucagon in the fed (absorptive) state?
The ratio of insulin to glucagon in the fed state is 4:1 (high insulin: glucagon ratio).
How does the high insulin: glucagon ratio in the fed state affects liver metabolism?
The high insulin: glucagon ratio in the liver promotes glycogen synthesis, fatty acid synthesis, and triglyceride synthesis.
How does the high insulin: glucagon ratio in the fed state affects muscle metabolism?
The high insulin: glucagon ratio stimulates protein and glycogen synthesis in muscle.
How does the high insulin: glucagon ratio in the fed state affects adipose tissue metabolism?
The high insulin: glucagon ratio in adipose tissue enhances triglyceride synthesis and inhibits triglyceride breakdown (lipolysis).
Does the utilisation of glucose in the brain change during the fed state?
No, glucose utilisation in the brain remains unchanged during the fed state.
What is the insulin-to-glucagon ratio in the fed state?
The fed state’s insulin-to-glucagon ratio is high (4:1).
What are the metabolic changes in the liver during the fed state?
In the liver, glucose is taken up, glycogen synthesis occurs, fatty acids are taken up and synthesised into triglycerides (TGs), and ketone bodies are not produced.
What are the metabolic changes in muscle during the fed state?
In muscle, glucose is taken up and oxidised for energy, amino acids (AA) are taken up for protein synthesis and energy, and fatty acids are not used as a significant energy source.
What are the metabolic changes in adipose tissue during the fed state?
In adipose tissue, glucose is taken up, fatty acids are taken up and synthesised into triglycerides (TGs), and TGs may be exported.
What are the metabolic changes in the brain during the fed state?
In the brain, glucose is the primary energy source, while fatty acids, glycerol, and ketone bodies are not utilised.
What is the insulin-to-glucagon ratio in the fasting state?
The fasting state’s insulin-to-glucagon ratio is low (0.8:1).
What are the metabolic changes in the liver during fasting?
In the liver, glycogen synthesis decreases, glycogenolysis (glycogen breakdown) increases, and gluconeogenesis is initiated to produce glucose from non-carbohydrate precursors such as lactate, alanine, and glycerol.
What happens to plasma glucose levels in the fasting state in relation to the liver?
Plasma glucose levels decrease as glucose no longer enters the liver due to the low affinity of the Glut2 transporter.
How does the reduced insulin-to-glucagon ratio affect liver metabolism in the fasting state?
The reduced insulin-to-glucagon ratio activates glycogenolysis (glycogen breakdown) and gluconeogenesis in the liver. Gluconeogenesis occurs from non-carbohydrate precursors such as lactate, alanine, and glycerol. This response is mediated by cAMP production in response to glucagon.
How does the low insulin-to-glucagon ratio affect glycogen, fat synthesis, and liver glycolysis in the fasting state?
The low insulin-to-glucagon ratio inhibits fasting glycogen synthesis, fat synthesis, and liver glycolysis.
How are amino acids utilised in the liver during fasting?
Proteins in the liver and other tissues are broken down into amino acids, which are then used as fuel for gluconeogenesis in the liver.
How are fatty acids utilised in the liver during fasting?
Fatty acids released from lipolysis are used as a source of energy through β-oxidation in the liver.
What are the effects of fatty acid oxidation on gluconeogenesis and glycolysis in the liver during fasting?
The oxidation of fatty acids produces citrate and acetyl CoA, which activate gluconeogenesis and inhibit glycolysis in the liver.
What happens to amino groups from proteins in the liver during the fasting state?
Amino groups from proteins are returned to the liver and detoxified through their conversion to urea.
How does the lowered insulin level affect glucose metabolism in adipose tissue?
Lowered insulin levels reduce glucose uptake into adipose tissue via the Glut4 transport system, severely inhibiting glucose metabolism via glycolysis.
What happens to triglycerides (TGs) in adipose tissue during fasting?
The reduced insulin-to-glucagon ratio triggers the mobilisation of TGs in adipose tissue. Some fatty acids are used within the tissue for energy production. In contrast, the remaining fatty acids are released into the bloodstream to support glucose-independent energy production in muscles and other tissues.
What happens to glycerol in adipose tissue during the fasting state?
Glycerol cannot be metabolised to produce energy in adipose tissue. Instead, it is recycled to the liver to support gluconeogenesis.
How does muscle adapt its energy source in the fasting state?
Muscle and other peripheral tissues switch to fatty acid oxidation as an energy source, inhibiting glycolysis and glucose utilisation.
How are proteins utilised in muscle during the fasting state?
Proteins are broken down into amino acids in muscle, and the carbon skeletons of amino acids can be used for energy production within the muscle or exported to the liver as alanine.