Lecture 32: Cellular Metabolism and Respiratory Response to Exercise Flashcards by Jorja Gantley

What energy source does muscle contraction need?

ATP

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How much ATP is stored in skeletal muscle cells?

Small amount, only provides several seconds of energy

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How is ATP synthesised during the start of short duration (seconds) exercise?

Muscle uses stored ATP first
1. Creatinine phosphate (Cr-P) mechanism to make more

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How is ATP synthesised during a few minutes of exercise?

Muscle uses stored ATP first
1. Cr-P
2. Anaerobic glycolysis

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How is ATP synthesised during minutes-hours of exercise?

Muscle uses stored ATP first
1. Cr-P
2. Anaerobic glycolysis
3. Oxidative phosphorylation of glucose
4. Oxidative phosphorylation of fatty acids

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How is ATP synthesised from creatine phosphate (Cr-P)?

Cr-P phosphorylates ADP to make ATP
▪ Phosphagen cycle or CrP-ATP system

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Describe the speed and life of ATP generated from Cr-P

Rapid ATP generation but short lived
▪ Anaerobic
▪ < 10 seconds
▪ 1 ATP per Cr-P molecule

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How is ATP synthesised from anaerobic glycolysis?

Breakdown of muscle glycogen into glucose
▪ Glucose → 2 pyruvate
▪ 2 pyruvate → 2 lactic acid + 2 ATP

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Describe the speed and production of ATP generated from anaerobic glycolysis:

Rapid ATP generation but low production
▪ Anaerobic
▪ 10 seconds to 2 minutes
▪ 2 ATP per glucose molecule

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How is ATP synthesised from oxidative phosphorylation of glucose?

▪ Glucose → 2 pyruvate
▪ 2 pyruvate → oxidative phosphorylation

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Describe the speed and production of ATP generated from oxidative phosphorylation of glucose:

Slower ATP generation but higher production
▪ Aerobic
▪ In mitochondria
▪ Minutes to hours
▪ 36 ATP per glucose molecule

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How is ATP synthesised from oxidative phosphorylation of fatty acids?

Fatty acids → oxidative phosphorylation

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Describe the speed and production of ATP generated from oxidative phosphorylation of fatty acids:

Slow ATP generation but very high production
▪ Aerobic
▪ In mitochondria
▪ Minutes to hours
▪ 100+ ATP per fatty acid molecule

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For exercise that lasts more than a few minutes, what determines the nutrients used and the mechanism of ATP synthesis?

Exercise intensity
Exercise duration

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What nutrients are used to make ATP when exercising for more than a few minutes?

Glucose
Fatty acids

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When exercising at a constant intensity for a long duration, what happens to muscle sources of fatty acids and glucose?

Deplete over time
Fatty acids; muscle triglycerides
Glucose; muscle glycogen

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When exercising at a constant intensity for a long duration, what happens to plasma sources of fatty acids and glucose?

Become more important
Fatty acids; from adipose tissue
Glucose; from liver glycogen and gluconeogenesis

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When exercising at a constant intensity for a long duration, how does the oxidative phosphorylation of fatty acids vs. glucose change? Why?

Oxidative phosphorylation of fatty acids increases
Oxidative phosphorylation and anaerobic glycolysis of glucose decreases
Body’s store of fatty acids is much greater than for glucose

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During low intensity exercise what produces the majority of ATP?

Oxidative phosphorylation of fatty acids

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During high intensity exercise what is the main fuel for ATP production?

Glucose via anaerobic glycolysis and oxidative phosphorylation of glucose

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Describe the exercise intensity and ATP production below aerobic threshold:

Intensity: maintained for long periods (hours)
ATP production:
main fuel is fatty acids >50% + some glucose
mainly made via oxidative phosphorylation
little anaerobic glycolysis ([lactate] low)

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Describe the exercise intensity and ATP production between aerobic and anaerobic thresholds:

Intensity: can’t be maintained for long periods (<1 hour)
ATP production:
> 50% of ATP production from glucose
increase in anaerobic glycolysis
blood [lactate] increases from baseline

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Describe the exercise intensity and ATP production above anaerobic threshold (based on ventilation):

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Intensity: can’t be maintained for long periods (minutes)
ATP production:
most/all from glucose
increase in anaerobic glycolysis from baseline
increasing H+ production causing hyperventilation
most ATP made from anaerobic glycolysis and OP of glucose

What is lactate threshold (based on blood [lactate]?

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[lactate] begins to increase exponentially
▪ anaerobic glycolysis increases AND the rate of lactate production exceeds the ability of the body to clear it from the blood
▪ fatigue increases rapidly at intensities above lactate threshold

For a relatively fit person what is the lactate threshold?

> 70% max intensity > 4mmol/L blood lactate

What is aerobic capacity and VO2 max?

Maximum amount of oxygen an individual can use during exercise

At the end of exercise what stores need to be replenished?

Skeletal muscle stores of: ▪ ATP ▪ Creatine phosphate ▪ Oxygen (myoglobin) ▪ Glycogen (slower)

At the end of exercise what needs to be cleared?

Metabolites: ▪ lactate/lactic acid

What is required to replenish skeletal muscle stores and clear metabolites?

Oxygen * Creating an oxygen debt - size dependent on intensity of exercise * Body consumes O2 at a higher rate after exercise - EPOC: excess post-exercise oxygen consumption - Ventilation remains higher for a period

Describe the rate of expenditure and restoration of energy systems during high intensity, short duration exercise:

* Higher rate of energy expenditure ▪ Proportionally larger oxygen debt ▪ Proportionally longer duration and higher intensity of EPOC: lasts longer than duration of exercise and larger increase in ventilation

Describe the rate of expenditure and restoration of energy systems during low intensity, long duration exercise:

* Lower rate of energy expenditure ▪ Proportionally smaller oxygen debt ▪ Proportionally shorter duration and lower intensity of EPOC

How are ATP stores replaced after exercise?

Making more ATP

How are Cr-P stores replaced after exercise?

Using ATP to regenerate Cr-P

What is restored on myoglobin after exercise?

Oxygen store

How is lactic acid used after exercise?

Removed from muscle, into the blood: 1. Liver converts it into glucose via gluconeogensis (uses 6 ATP) 2. Other cells use it to create more ATP by converting it back into pyruvate

Give an example of where lactate is formed and where is it donated:

Lactate formed in ‘fast-twitch’ fibres is donated to ‘slow-twitch’ fibres to use for ATP production in the mitochondria

What systems work together during the respiratory response to exercise?

1. Cardiovascular: CO, vascular response 2. Respiratory: ventilation, gas diffusion 3. Cellular: ATP synthesis

How is Fick's principle arranged to determine oxygen consumption (VO2)?

VO2 = Q ( CAO2 - CVO2) Q = cardiac output CAO2 = content of O2 in arteries CVO2 = content of O2 in veins

What is VCO2?

Carbon dioxide production

Describe the changes in ventilation during steady-state low and moderate intensity exercise:

1. Sudden increase in ventilation at exercise onset: feedforward response 2. Gradual increase until a steady-state is reached: ▪ when V̇O2 and V̇CO2 balance with V̇A, ventilation plateaus 3. Sustained increase in ventilation for a period after the end of after exercise to replace O2 debt: EPOC

What happens to ventilation, VE, when exercise intensity increase during low/med intensity exercise?

It increases

What happens to venous and arterial PO2 when exercise intensity increase during low/med intensity exercise?

* Venous: increases because more O2 is extracted from systemic blood by exercising muscles (↑VO2) * Arterial: constant because increase in VO2 is matched by increase in VE (more O2 breathed in to replace)

What happens to venous and arterial PCO2 when exercise intensity increase during low/med intensity exercise?

* Venous: increases because more CO2 is produced by exercising muscles (↑VCO2) * Arterial: constant because increase in VCO2 is matched by increase in VE (extra CO2 is breathed out)

What happens to arterial [H+] when exercise intensity increase during low/med intensity exercise?

Remains constant because: 1. Arterial PCO2 is constant so no extra H+ is made from CO2 2. Blood [lactate/lactic acid] is low

What physiological processes occur when 'getting ready' for exercise?

Feedforward increase in VE immediately at the start of exercise ▪ Primary motor cortex and exercising muscle proprioceptors * Exercise central command * Medullary respiratory centres * Respiratory system

What occurs overall during low/med intensity exercise?

Ventilation increases in proportion to exercise intensity

Describe the response of central and peripheral chemoreceptors, during low/med intensity exercise:

* Respond to ↑CO2 * Medullary respiratory centres * Respiratory system = ↑ Ventilation - Removes more CO2 & maintains arterial PCO2

Describe the response of muscle mechano- & chemoreceptors, during low/med intensity exercise:

* Respond to muscle contraction and metabolites * Medullary respiratory centres * Respiratory system = ↑ Ventilation

Describe the response of central thermoreceptors, during low/med intensity exercise:

* Respond to ↑core body temperature * * Medullary respiratory centres * Respiratory system = ↑ Ventilation

Describe the response of SNS during low/med intensity exercise:

* Exercise ↑ SNS activity * Release of adrenaline from adrenal glands * Bronchodilation * ↑ Ventilation

What causes hyperventilation during high intensity exercise?

Acid production - anaerobic threshold

Describe the anaerobic threshold and its effect on ventilation during high intensity exercise?

▪Anaerobic glycolysis increases, increasing lactate and H+ * Arterial [H+] increases: ▪ metabolic acidosis ▪ increased production of CO2 to buffer the [H+] * Increases firing of peripheral chemoreceptors to medullary respiratory centers ▪ Increases ventilation

What occurs above the anaerobic threshold?

V̇E and V̇CO2 increase disproportionately more than V̇O2

What happens to ventilation, VE, during high intensity exercise?

Hyperventilation - VE increases disproportionately

What happens to venous and arterial PO2, during high intensity exercise?

* Venous: Decreases * Arterial: Constant

What happens to arterial PCO2, during high intensity exercise?

* Venous: Increases because more CO2 is produced by exercising muscles (↑↑VCO2) * Arterial: Decreases due to hyperventilation

What response occur during high intensity exercise?

1. Muscle mechano- & chemoreceptors 2. Increased core body temperature 3. SNS: increased adrenaline

Lecture 32: Cellular Metabolism and Respiratory Response to Exercise Flashcards

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