Energy metabolism during excersise Flashcards Preview

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Flashcards in Energy metabolism during excersise Deck (43)
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1
Q

What is the role of ATP in muscle contraction?

A
  • ATP is the direct fuel for contraction, supplying the ATPase activity of myosin
  • Therefore, ATP is needed to support muscle contraction, with ATP utilisation increasing more than 100-fold in milliseconds
2
Q

At rest muscle has approx. ___ mmol of ATP per kg wet weight

During vigorous contraction this lasts

In the short-term, muscle can increase its rate of production of ATP _____ fold

A

5

2

2-100

3
Q

How does muscle increase ATP production during excersise?

A

•Initially the main fuel for this is glycogen stored within the muscle itself; however as time goes on, other tissues need to co-operate to provide fuel for energy production

4
Q

How does Muscle metabolism work at rest (post-absorptive state)?

A
  • In resting muscle, glycogen stores are maintained/replenished
  • Oxidative metabolism of fatty acids provides energy for the muscle

Little lactate produced as pyruvate is used for glycogen synthesis or used in TCA cycle as sufficient oxygen present in the muscle

ATP not generated via PC system at rest

5
Q

What occurs in the muscle metabolism at the onset of excersise?

A
  1. Glycogenolysis provides fuel source
  2. Increase in O2 consumption for ox phos
  3. Increased blood flow to muscles due to local mediators (NO) and β-adrenergic stimulation of vascular smooth muscles
6
Q

Amount of energy derived from glycolysis and ox phos is dependent on the _________ and _________ of the exercise

A

Amount of energy derived from glycolysis and ox phos is dependent on the intensity and duration of the exercise

7
Q

How is Mobilisation of muscle glycogen during exercise controlled?

A

Glycogen mobilization in the muscle is controlled by Ca2+ levels in the cytoplasm of muscle cells, levels of AMP and by adrenaline.

8
Q

How does Mobilisation of muscle glycogen during exercise occur?

A
9
Q

What is the role of Ca2+ in muscle contraction?

A
  • Increase in Ca2+ concentration is the signal for muscle contraction
  • Also increases muscle glycogen breakdown by activating glycogen phosphorylase to supply the energy required
  • Stimulates the production of nitric oxide which causes vasodilation of the blood vessels and increased blood flow
10
Q

What are the Characteristics of Skeletal Muscle Blood Flow?

A
  • Skeletal muscle accounts for about 20% of cardiac output at rest; can increase to more than 80% during extreme physical exertion.
  • Coordinated, rhythmical contractions (e.g. running) enhance blood flow by means of the skeletal muscle pump mechanism.
11
Q

What is blood flow determined by?

A
  • Blood flow is strongly determined by local regulatory (tissue and endothelial) factors such as tissue hypoxia, adenosine, K+, CO2, H+, and nitric oxide
  • Vascular β2-adrenoceptors result in vasodilation when stimulated by agonists such as adrenaline
12
Q

How is metabolism hormonally controlled during excersise?

A
13
Q

What are the 3 systems for forming ATP in muscle?

A
14
Q

Complete the table on the 3 systems for forming ATP during excersise

A
15
Q

Which pathway has the highest energy?

A

Anaerobic energy pathways have a much higher power (rate of ATP production) but smaller capacity (total ATP produced) than aerobic pathways

In terms of aerobic metabolism, carbohydrate oxidation has a higher power output but a lower capacity than fat oxidation (discussed on Slide 23)

16
Q

What is Phosphocreatine (or creatine phosphate)?

A

PC: An extra source of energy in muscle cells

17
Q

What is the role of phosphocreatinine?

A
  • First top-up source for muscle ATP
  • At rest, muscle has about 100 mmol creatine phosphate (phosphocreatine) per kg dry weight. During vigorous contraction this lasts approx 16 secs
  • May be enough for a 100-200 metre sprint
18
Q

What is the equation for phosphocreatinine?

A
19
Q

__________ and _______ are greatly stimulated during contraction

A

•Glycogen breakdown and glycolysis are greatly stimulated during contraction

20
Q

When does anaerobic glycolysis occur?

A
  • If the increased rate of metabolism outstrips the oxygen supply, glycolysis can proceed anaerobically
  • Much less ATP is produced and lactate builds up
  • Even when the oxygen supply is sufficient, pyruvate may be formed faster than it can be oxidised. This also causes the accumulation of lactate
21
Q

What is the cori cycle?

A

Lactate is used by the liver to regenerate glucose which can be transferred back to the muscle for energy production. If there is insufficient blood flow through the muscle, lactic acid builds up in the muscle.

22
Q

When does aerobic metabolism occur during exersise?

A
  • In addition to glycogen, muscle also uses fatty acids from the adipose tissue to maintain ATP levels.
  • However, aerobic metabolism of glucose and fatty acid oxidation are dependent on an adequate oxygen supply to the muscle
  • Oxygen is necessary for any ATP production via fatty acid oxidation
23
Q

What is fatigue?

A
  • Inability to maintain desired power output
  • Occurs when rate of ATP utilization exceeds its rate of synthesis
24
Q

How does fatigue occur?

A
  • Accumulation of pyruvate and lactic acid in the contracting muscle result in a decline in force generated
  • Due to decrease in muscle pH
  • Glycolysis inhibited by H+ from lactic acid
25
Q

What proportion of metabolism do these take up at different distances?

A
26
Q

What is the effect of intensity and duration of exercise on method of ATP synthesis?

A
  • Only 2 fuels are used in short sprints to replenish ATP, phosphocreatine and anaerobic glycogen breakdown to lactate
  • As the distance increases, phosphocreatine levels are exhausted and the muscle relies solely on glycogen breakdown either anaerobically to lactate or aerobically to CO2 via the TCA cycle
  • During the marathon, the muscles are reliant on oxidative metabolism of glycogen and also glucose from the liver and fatty acids from the adipose tissue
27
Q

Lable the type of metabolism

A
28
Q

How does muscle metabolism work during a sprint?

A

Fuel: PC & anaerobic glycolysis

  • Catecholamines stimulate glycogen breakdown in muscle which is converted anaerobically to lactate. Phosphocreatine is converted to creatine with the transfer of Pi to ADP to form ATP
  • Blood vessels are compressed during sprinting isolating the cells from the blood supply making the muscles reliant on anaerobic energy production from glycogen
  • Large quantities of lactic acid produced as glycolysis proceeds which the liver can use to maintain blood glucose levels via gluconeogenesis
29
Q

How does muscle metabolism work during a middle distance run?

A
  • As the distance increases aerobic oxidation of glycogen makes up 30% of the ATP required to support contraction. Some of the oxygen required may come from oxymyoglobin in the muscle
  • Lactate is still a major end product of glycogen metabolism contributing 65% of the ATP required
  • The contribution of phosphocreatine to the ATP required becomes less and less as the distance increases. At 800 metres it contributes 5% and essentially zero over 1500 metres
30
Q

How does muscle metabolism work during the first 10 minutes of a marathon?

A

•Muscle glycogen and glucose from the liver are used to power muscles, mainly through glycolysis. Increased vasodilation in the muscles increases O2 supply increasing the aerobic glycogen utilisation and ATP production.

Glycogen breakdown stimulated by increased AMP and adrenalin release

•Fatty acids are mobilised by the release of adrenalin to allow liver to maintain blood glucose levels by the provision of energy and the glycerol backbone

31
Q

How does muscle metabolism work 30 minutes - 2 hours into a marathon?

A
  • ATP generated via oxidation of glucose and fatty acids. Increased reliance on fatty acid oxidation over this longer timespan of relatively intense exercise.
  • Lactate, glycerol and muscle amino acids used to support glucose production by the liver, energy being derived from fatty acid oxidation.
32
Q

Oxidation of carbohydrate or fat in endurance exercise?

A
  • Fats alone can supply most of the needs for resting muscle, but exercising muscle have an absolute requirement for some glucose
  • Fatty acid breakdown during extended periods of exercise proceeds on a continual background level of glucose metabolism
  • This requirement for a background level of glucose metabolism increases with exercise intensity
33
Q

What happens to muscle metabolism at 2+ hours in a marathon?

A
  • About 90% of liver glycogen used. Insulin levels remain very low and glucagon levels elevated.
  • Ketone bodies produced by the liver and may be used by muscle to generate ATP (in addition to fatty acids)
34
Q

What does hitting the wall mean?

A

•Hitting the wall means that exercise intensity drops because of a lack of available ATP

35
Q

What causes ‘hitting the wall’?

A
  • A marathon requires about 700g of glycogen, whereas muscle and liver normally contain only 500g, therefore glycogen stores are largely depleted after 20 miles.
  • Body switches to fatty acids as main source of energy with little glucose metabolism.
  • Fatty acid oxidation only generates sufficient ATP for 50% of maximum power output and pace decreases as glycogen depleted – known as ‘hitting the wall’.
36
Q

Why is there a potential for hypoglycaemia in final stages of a marathon?

A
  • With prolonged high-intensity exercise, liver glucose output may fall below muscle glucose uptake thus resulting in hypoglycaemia
  • Typical symptoms of confusion, lack of cognitive function, lactic acidosis and exhaustion may occur (less likely with training)
37
Q

The Confused Marathon Runner

Jon entered the stadium for the final lap of his marathon race. He was well ahead of the pack. In the last minute or so, he seemed to become confused, his legs buckled and then he collapsed multiple times. What went wrong?

A
  • In brief, Jon’s muscles consumed the fuels that were needed by his brain. Therefore there was not a sufficient supply of fuels to permit his brain cells to synthesize enough ATP for their needs.
  • Muscle can use fatty acids or glucose for energy. High use of fatty acids requires their efficient delivery to muscle, and also efficient delivery of oxygen. If either is lacking glucose will be used.
  • At the end of the race, Jon is pushing his resources to the limit. Excess use in muscle takes glucose from brain.
  • A slight over demand on glucose can deplete blood and starve the brain of this energy source. Normally glycogen in liver will replace it, but at the end of the race, liver glycogen and muscle glycogen also are depleted.
  • The brain can use glucose or ketoacids, but ketoacids are not available to the brain as Jon is not starved. The use of ketoacids by the brain requires a higher concentration of ketones in the blood than would be present after a marathon. Upregulation of the enzymes required to convert ketones into acetyl-CoA is also required; this takes around 3 days. Hence only glucose can fuel his brain.
  • As a result Jon’s brain is starved of glucose and he suffers from confusion and collapses with exhaustion
38
Q
  1. In the resting state briefly explain how skeletal muscle derives its energy?
A

Answer: From the aerobic oxidation of fatty acids via beta-oxidation with the acetyl CoA feeding into the TCA cycle and electron transport chain.

39
Q
  1. Explain the mechanism by which the muscles cope with the increased demand for oxygen during a brisk walk / jog.
A

Answer: Vasodilation and increased blood supply to the muscles results from Ca2+-dependent nitric oxide production and β-adrenergic activation of the vascular smooth muscle.

40
Q
  1. Briefly describe the metabolic changes that occur to sustain muscle contraction during a 100m sprint.
A

Answer: During sprinting phosphocreatine is used as a major substrate to generate ATP to support contraction

•catecholamines stimulate glycogen breakdown in muscle to provide 50% of the energy via glycolysis.

· With the intense muscle contraction blood vessels become compressed isolating the cells from the blood supply making the muscles reliant on anaerobic energy production with large quantities of lactic acid produced as the end product of glycolysis.

41
Q

After the first 10 minutes of a marathon run:

(i) What is the major fuel used to support contraction?
(ii) What is the metabolic end product of this process and how is it reutilized?

A

Answers: (i) Glycogen

(ii) Glycogen is converted to lactic acid via anaerobic glycolysis. The lactate is released into the bloodstream for transport to the liver for conversion into glucose via gluconeogenesis; this is then returned to the muscle completing the Cori cycle.

42
Q
  1. Briefly describe in metabolic terms the process known as ‘hitting the wall’ after 20 miles of a marathon.
A

Answer: Muscle and liver glycogen are largely depleted after 20 miles.

•Body has to switch back to fatty acids as main source of energy,

(aerobic metabolism). This is not as efficient in terms of ATP

production while running.

•Lactate, glycerol and muscle amino acids are used to support

glucose production by the liver to prevent hypoglycaemia, energy being derived from fatty acid oxidation

43
Q
  1. What two physiological mechanism(s) exist to ensure adequate oxygenation of the muscle during exercise?
A

Answer: The rise in Ca2+ at the onset of contraction results in the local release of nitric oxide which causes vasodilation.

•Adrenaline interacts with β-adrenergic receptors within the blood vessels causing relaxation and vasodilation.