Energy, metabolism and exercise

Question 1

What are the three states of metabolism in relation to feeding?

Answer 1

The three states are the fed state, post-absorptive state, and starvation state.

Question 2

What are the key metabolic changes that occur from the absorptive state to the post-absorptive state?

Answer 2

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.

Question 3

Which energy source is predominant in most cells during the absorptive state?

Answer 3

Glucose is the primary energy source for most cells during the absorptive state

Question 4

Which energy source becomes dominant in most cells during the post-absorptive state?

Answer 4

Triglycerides become the primary energy source for most cells during the post-absorptive state.

Question 5

What is the molar ratio of insulin to glucagon in the blood during the fed state?

Answer 5

The fed state is characterized by a high insulin and low glucagon ratio.

Question 6

What is the molar ratio of insulin to glucagon in the blood during the fasting state?

Answer 6

The fasting state is characterized by a low insulin and high glucagon ratio.

Question 7

When does prolonged fasting or starvation occur?

Answer 7

Prolonged fasting or starvation occurs when the fasting state lasts for more than 12 hours.

Question 8

What is the ratio of insulin to glucagon in the fed (absorptive) state?

Answer 8

The ratio of insulin to glucagon in the fed state is 4:1 (high insulin: glucagon ratio).

Question 9

How does the high insulin: glucagon ratio in the fed state affects liver metabolism?

Answer 9

The high insulin: glucagon ratio in the liver promotes glycogen synthesis, fatty acid synthesis, and triglyceride synthesis.

Question 10

How does the high insulin: glucagon ratio in the fed state affects muscle metabolism?

Answer 10

The high insulin: glucagon ratio stimulates protein and glycogen synthesis in muscle.

Question 11

How does the high insulin: glucagon ratio in the fed state affects adipose tissue metabolism?

Answer 11

The high insulin: glucagon ratio in adipose tissue enhances triglyceride synthesis and inhibits triglyceride breakdown (lipolysis).

Question 12

Does the utilisation of glucose in the brain change during the fed state?

Answer 12

No, glucose utilisation in the brain remains unchanged during the fed state.

Question 13

What is the insulin-to-glucagon ratio in the fed state?

Answer 13

The fed state’s insulin-to-glucagon ratio is high (4:1).

Question 14

What are the metabolic changes in the liver during the fed state?

Answer 14

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.

Question 15

What are the metabolic changes in muscle during the fed state?

Answer 15

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.

Question 16

What are the metabolic changes in adipose tissue during the fed state?

Answer 16

In adipose tissue, glucose is taken up, fatty acids are taken up and synthesised into triglycerides (TGs), and TGs may be exported.

Question 17

What are the metabolic changes in the brain during the fed state?

Answer 17

In the brain, glucose is the primary energy source, while fatty acids, glycerol, and ketone bodies are not utilised.

Question 18

What is the insulin-to-glucagon ratio in the fasting state?

Answer 18

The fasting state’s insulin-to-glucagon ratio is low (0.8:1).

Question 19

What are the metabolic changes in the liver during fasting?

Answer 19

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.

Question 20

What happens to plasma glucose levels in the fasting state in relation to the liver?

Answer 20

Plasma glucose levels decrease as glucose no longer enters the liver due to the low affinity of the Glut2 transporter.

Question 21

How does the reduced insulin-to-glucagon ratio affect liver metabolism in the fasting state?

Answer 21

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.

Question 22

How does the low insulin-to-glucagon ratio affect glycogen, fat synthesis, and liver glycolysis in the fasting state?

Answer 22

The low insulin-to-glucagon ratio inhibits fasting glycogen synthesis, fat synthesis, and liver glycolysis.

Question 23

How are amino acids utilised in the liver during fasting?

Answer 23

Proteins in the liver and other tissues are broken down into amino acids, which are then used as fuel for gluconeogenesis in the liver.

Question 24

How are fatty acids utilised in the liver during fasting?

Answer 24

Fatty acids released from lipolysis are used as a source of energy through β-oxidation in the liver.

Question 25

What are the effects of fatty acid oxidation on gluconeogenesis and glycolysis in the liver during fasting?

Answer 25

The oxidation of fatty acids produces citrate and acetyl CoA, which activate gluconeogenesis and inhibit glycolysis in the liver.

Question 26

What happens to amino groups from proteins in the liver during the fasting state?

Answer 26

Amino groups from proteins are returned to the liver and detoxified through their conversion to urea.

Question 27

How does the lowered insulin level affect glucose metabolism in adipose tissue?

Answer 27

Lowered insulin levels reduce glucose uptake into adipose tissue via the Glut4 transport system, severely inhibiting glucose metabolism via glycolysis.

Question 28

What happens to triglycerides (TGs) in adipose tissue during fasting?

Answer 28

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.

Question 29

What happens to glycerol in adipose tissue during the fasting state?

Answer 29

Glycerol cannot be metabolised to produce energy in adipose tissue. Instead, it is recycled to the liver to support gluconeogenesis.

Question 30

How does muscle adapt its energy source in the fasting state?

Answer 30

Muscle and other peripheral tissues switch to fatty acid oxidation as an energy source, inhibiting glycolysis and glucose utilisation.

Question 31

How are proteins utilised in muscle during the fasting state?

Answer 31

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.

Question 32

What happens to glycogen in muscle during the fasting state?

Answer 32

Glycogenolysis does not occur in skeletal muscle during fasting since there are no glucagon receptors in skeletal muscle to activate it.

Question 33

What is the insulin-to-glucagon ratio in the fasting state?

Answer 33

The fasting state’s insulin-to-glucagon ratio is low (0.8).

Question 34

How does the brain utilise fuel during the fasting state?

Answer 34

Despite the absence of dietary glucose, the brain continues metabolising glucose as its primary fuel source during fasting.

Question 35

Why can’t the brain switch to fatty acids as a fuel source during fasting?

Answer 35

The brain cannot utilise fatty acids as a fuel source during fasting since free fatty acids do not cross the blood-brain barrier.

Question 36

What is the insulin-to-glucagon ratio in the starved state?

Answer 36

The starved state’s insulin-to-glucagon ratio is very low (0.4).

Question 37

How does the liver respond to the low insulin levels in the starved state?

Answer 37

The liver switches to glucose production in the starved state due to low insulin levels. Glycogen stores become depleted, activating gluconeogenesis to produce glucose for export to the brain and other tissues. Additionally, the liver produces ketone bodies from Acetyl CoA for export as a fuel source for other tissues, such as the brain and muscles.

Question 38

How does adipose tissue respond to low insulin levels in the starved state?

Answer 38

Low insulin levels stimulate lipolysis in adipose tissue, breaking triglycerides into fatty acids and glycerol. Fatty acids are then exported and used by other tissues, like muscle, for energy needs. Glycerol is transported to the liver for utilisation in gluconeogenesis.

Question 39

What metabolic changes occur in muscle during the starved state?

Answer 39

In the starved state, muscle uses fatty acids as fuel. This helps spare protein breakdown. However, specific details about muscle metabolism in the starved state are not provided.

Question 40

How does the brain adapt its fuel source in the starved state?

Answer 40

In the starved state, the brain continues to rely on glucose as its primary fuel source. Gluconeogenesis in the liver ensures a supply of glucose for export to the brain and other tissues.

Question 41

What are the key metabolic changes in the starved state?

Answer 41

In the starved state, the liver switches to glucose production through gluconeogenesis, ketone bodies are produced and exported, and fatty acid catabolism provides energy for gluconeogenesis. Adipose tissue undergoes lipolysis, releasing fatty acids for energy use, while glycerol is utilised in gluconeogenesis. Muscle primarily relies on fatty acids, and the brain utilises glucose as its main fuel source.

Question 42

How is glucose provided in the fed state?

Answer 42

In the fed state, glucose is provided by the diet.

Question 43

Where does most glucose come from in the fasted state?

Answer 43

In the fasted state, most of the glucose is provided by the breakdown of liver glycogen, with increasing amounts produced through gluconeogenesis.

Question 44

How is glucose primarily generated in the starved state?

Answer 44

In the starved state, most glucose comes from gluconeogenesis, utilising protein and fats breakdown products such as amino acids and glycerol.

Question 45

What is the main energy currency used to support muscle contraction during exercise?

Answer 45

ATP (adenosine triphosphate) is the main energy currency to support muscle contraction during exercise.

Question 46

How does the production of ATP increase during short-term exercise?

Answer 46

During short-term exercise, the muscle can increase its rate of ATP production by 20-100 fold. The main fuel for ATP production at this stage is glycogen stored within the muscle.

Question 47

What happens as exercise continues and more fuel is needed for ATP production?

Answer 47

As exercise continues, other tissues must cooperate in fueling ATP production in the muscles.

Question 48

What is the role of ATP in muscle contraction?

Answer 48

ATP is the direct fuel for muscle contraction by supplying the ATPase activity of myosin, a protein involved in muscle contraction.

Question 49

What are the three systems for forming ATP in muscle?

Answer 49

The three systems for forming ATP in muscle are the anaerobic ATP-PC, lactic acid, and aerobic oxygen systems.

Question 50

What fuels are used in the anaerobic ATP-PC system?

Answer 50

The anaerobic ATP-PC system primarily uses phosphocreatine (PC) and glycogen as fuel sources.

Question 51

Is oxygen required in the anaerobic ATP-PC system?

Answer 51

No, oxygen is not required in the anaerobic ATP-PC system.

Question 52

Which ATP production system is the fastest?

Answer 52

The anaerobic ATP-PC system is the fastest ATP production system.

Question 53

Which ATP production system has the highest ATP production rate?

Answer 53

The aerobic oxygen system has the highest ATP production rate.

Question 54

What is the role of creatine phosphate (phosphocreatine) in muscle cells?

Answer 54

Creatine phosphate (phosphocreatine) serves as the first “top-up” source for muscle ATP (adenosine triphosphate).

Question 55

How long does the supply of creatine phosphate last during vigorous muscle contraction?

Answer 55

During vigorous contraction, the supply of creatine phosphate lasts approximately 16 seconds.

Question 56

Is the supply of creatine phosphate sufficient for longer-duration activities?

Answer 56

The supply of creatine phosphate may be enough for a short-duration activity, such as a 100-200 meter sprint.

Question 57

What is the primary fuel source for energy production during exercise?

Answer 57

Glycolysis, the breakdown of glycogen, provides the initial fuel source for energy production during exercise.

Question 58

What determines the energy derived from glycolysis and respiration during exercise?

Answer 58

The amount of energy derived from glycolysis (anaerobic) and respiration (aerobic) depends on the intensity and duration of the exercise.

Question 59

What factors contribute to increased blood flow to muscles during exercise?

Answer 59

Increased blood flow to muscles during exercise is facilitated by local mediators such as nitric oxide (NO) and β-adrenergic stimulation of vascular smooth muscles.

Question 60

What are the two primary fuels replenishing ATP in short sprints?

Answer 60

Phosphocreatine and anaerobic glycogen breakdown to lactate are the primary fuels for replenishing ATP in short sprints.

Question 61

How does the muscle rely on fuel sources as the distance increases during a marathon?

Answer 61

As the distance increases during a marathon, the muscle exhausts its phosphocreatine levels and relies solely on glycogen breakdown. This breakdown can occur anaerobically to lactate or aerobically to CO2 via the TCA cycle.

Question 62

What fuel sources are relied upon by the muscles during a marathon?

Answer 62

During a marathon, the muscles rely on the oxidative metabolism of glycogen, glucose from the liver and fatty acids from adipose tissue.

Question 63

What is the body’s metabolic state during the resting stage of a marathon?

Answer 63

During the resting stage of a marathon, the body is in a state of rest, and energy expenditure is relatively low.

Question 64

What is the contribution of aerobic glycogen oxidation to ATP production during the middle distance of a marathon?

Answer 64

As the distance increases, aerobic oxidation of glycogen makes up 30% of the ATP required to support muscle contraction.

Question 65

What is the major end product of glycogen metabolism during the middle distance of a marathon?

Answer 65

Lactate is still a major end product of glycogen metabolism, contributing 65% of the ATP required.

Question 66

How does the contribution of phosphocreatine to ATP production change as the distance increases during a marathon?

Answer 66

As the distance increases, the contribution of phosphocreatine to the required ATP becomes less significant. At 800 meters, it contributes 5% and essentially zero over 1500 meters.

Question 67

What happens if the rate of metabolism during exercise exceeds the oxygen supply?

Answer 67

If the rate of metabolism exceeds the oxygen supply, glycolysis can proceed anaerobically. This leads to the production of less ATP and the accumulation of lactate.

Question 68

Can lactate accumulate even when there is sufficient oxygen supply?

Answer 68

Yes, even when there is sufficient oxygen supply, pyruvate may be formed faster than it can be oxidised, resulting in lactate accumulation.

Question 69

What stimulates glycogen breakdown and glycolysis during muscle contraction?

Answer 69

Glycogen breakdown and glycolysis are greatly stimulated during muscle contraction.

Question 70

What is the Cori Cycle?

Answer 70

The Cori Cycle is a metabolic pathway in which lactate produced in the muscle is transported to the liver and converted back into glucose. The glucose can then be transferred back to the muscle for energy production.

Question 71

What happens if there is insufficient blood flow during exercise?

Answer 71

Lactic acid (lactate) can build up in the muscle with insufficient blood flow.

Question 72

What happens to muscle and liver glycogen during exercise?

Answer 72

Muscle and liver glycogen are depleted during exercise.

Question 73

What symptoms can occur in cases of hypoglycemia during exercise?

Answer 73

Hypoglycemia, characterised by low blood glucose levels, can lead to confusion, lack of cognitive function, lactic acidosis, and exhaustion. Regular training can help mitigate these symptoms.

Question 74

What is fatigue in the context of exercise?

Answer 74

Fatigue is the inability to maintain the desired power output during exercise.

Question 75

What causes fatigue during exercise?

Answer 75

Fatigue occurs when the rate of ATP utilisation exceeds its synthesis rate. Accumulation of pyruvate and lactic acid in the contracting muscle leads to a decline in the force generated. The decrease in muscle pH, caused by the accumulation of lactic acid, inhibits glycolysis.

Question 76

What controls human metabolism oscillation between the fed and fasting states?

Answer 76

The circulating hormone insulin and glucagon levels control the oscillation between the fed and fasting states in human metabolism.

Question 77

What metabolic changes occur during fasting/starvation states?

Answer 77

In fasting/starvation states, the insulin/glucagon ratio becomes increasingly low, signalling the fasting/starved states. The liver changes its metabolism to ensure a supply of blood glucose through glycogenolysis (glycogen breakdown) and gluconeogenesis (production of glucose from non-carbohydrate sources).

Question 78

How does the body obtain energy under starvation conditions?

Answer 78

Under starvation conditions, triacylglycerols in adipose tissue are broken down through lipolysis, releasing fatty acids that become the liver’s and muscles’ major energy source. The liver uses fatty acids for gluconeogenesis and produces ketone bodies from acetyl CoA, which all tissues, including the brain, can use.

Question 79

How does energy utilisation in exercise vary based on vigour and duration?

Answer 79

Short sprints (100 m) are met by phosphocreatine and anaerobic glycogen breakdown via glycolysis. Medium distance (800-1500 m) relies on glycogen breakdown through glycolysis and aerobic respiration. Long-distance exercises (marathons) rely on fatty acid oxidation through aerobic respiration.