L31. Cellular Metabolism and Respiratory Response to Exercise Flashcards
(30 cards)
Cellular metabolism during exercise?
Muscle contraction needs energy: ATP
- The cross-bridge cycle converts chemical energy (ATP) to mechanical force (power stroke)
BUT
- Skeletal muscle cells only have a small amount of stored ATP
- Only enough to provide several seconds of energy
- Need to produce more ATP rapidly
ATP synthesis at the START of exercise/muscle contraction?
Short duration (seconds):
- ATP (already synthesised)
1. Creatinine phosphate (Cr-P)
A few minutes:
- ATP (already synthesised)
1. Cr-P
2. Anaerobic glycolysis
Minutes - hours:
- ATP (already synthesised)
1. Cr-P
2. Anaerobic glycolysis
3. Oxidative phosphorylation of glucose
4. Oxidative phosphorylation of fatty acids
ATP synthesis - creatine phosphate (Cr-P)?
- Phosphorylation of ADP by creatine phosphate (Cr-P) to make ATP
- Phosphagen cycle or CrP-ATP system
- Rapid ATP generation but short lived
- Anaerobic (doesn’t require oxygen)
- < 10 seconds
- 1 ATP per molecule of Cr-P
ATP synthesis - anaerobic glycolysis?
- Breakdown of muscle glycogen into glucose
- Glucose –> 2 pyruvate
- 2 pyruvate –> 2 lactic acid + 2 ATP
- Rapid ATP generation but low production
- Anaerobic (doesn’t require oxygen)
- 10 seconds to 2 minutes
- 2 ATP per molecule of glucose
ATP synthesis - oxidative phosphorylation of glucose?
- Oxidative phosphorylation of glucose
- Glucose –> 2 pyruvate
- 2 pyruvate –> oxidative phosphorylation
- Slower ATP generation but higher production
- Aerobic (needs oxygen)
- In the mitochondria
- Minutes to hours
- 36 ATP per molecule of glucose
ATP synthesis - oxidative phosphorylation of fatty acids?
- Oxidative phosphorylation of fatty acids
- Fatty acids to oxidative phosphorylation
- Slow ATP generation but very high production
- Aerobic (needs oxygen)
- In the mitochondria
- Minutes to hours
- 100+ ATP per fatty acid molecule
Cellular metabolism during exercise?
When performing exercise which lasts for more than a few minutes the nutrient/s which is used to make ATP, and the mechanism of ATP synthesis is determined by two things:
1. Exercise intensity
2. Exercise duration
Nutrient used to make ATP:
- Glucose
- Fatty acids
Mechanism of ATP synthesis:
- Anaerobic glycolysis
- Oxidative phosphorylation of:
* Glucose
* Fatty acids
Exercise duration?
When exercising at a relatively constant level of intensity (‘steady-state’) for a long period of time the type of fuel used to make ATP and the source of the fuels change:
- Muscle source of fatty acids (muscle triglycerides) and glucose (muscle glycogen) deplete over time
- Plasma sources of fatty acids (from adipose tissue) and glucose (from liver glycogen and gluconeogenesis) become more important
The overall contribution of oxidative phosphorylation of fatty acids increases, and oxidative phosphorylation and anaerobic glycolysis of glucose decreases because the body’s store of fatty acids is much greater than for glucose
Exercise intensity?
- During low intensity exercise the majority of ATP is produced from oxidative phosphorylation of fatty acids
- During high intensity exercise glucose becomes the main fuel for ATP production via anaerobic glycolysis and oxidative phosphorylation of glucose
Exercise intensity - thresholds?
Below aerobic threshold (low intensity, high duration):
- Exercise intensity can be maintained for long periods (hours)
- ATP production:
* Main fuel is fatty acids (>50%) + some glucose
* Mostly made via oxidative phosphorylation (OP) of fatty acids
* Some OP of glucose
* A little anaerobic glycolysis (lactate concentration low)
Between aerobic and anaerobic thresholds:
- Intensity cannot be maintained for long periods (<1 hour)
- ATP production:
* >50% of ATP production from glucose
* Increase in anaerobic glycolysis
* Blood lactate concentration increases from baseline levels
Above anaerobic threshold (based on ventilation) (high intensity, low duration):
- Intensity cannot be maintained for long periods (minutes)
- ATP production:
* Most/all from glucose
* Increase in anaerobic glycolysis from baseline levels increasing H+ production causing hyperventilation
* Most ATP made from anaerobic glycolysis and OP of glucose
Exercise intensity - lactate threshold?
Lactate threshold (based on blood lactate concentration):
- When lactate concentration 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
Exercise intensity - aerobic capacity and VO2 max?
The maximum amount of oxygen an individual can use during exercise
Restoring energy systems after exercise?
At the end of exercise, the body needs to:
- Replenish skeletal muscle stores of:
* ATP
* Creatine phosphate
* Oxygen (myoglobin)
* Glycogen (slower)
- Clear metabolites:
* Lactate/lactic acid
These process require oxygen, creating an ‘oxygen debt’:
- The amount of oxygen required to restore the body to its pre-exercise state
* ‘Size’ of the oxygen debt is determined by the intensity of the exercise
- The body continues to consume oxygen at a higher rate than normal for a period after exercise
* EPOC: excess post-exercise oxygen consumption
* Ventilation remains higher than at rest for a period at the end of exercise
Restoring energy systems after exercise - different intensities?
High intensity, short duration exercise:
- Higher rate of energy expenditure
- Proportionally larger oxygen debt
- Proportionally longer duration and higher intensity of EPOC
* EPOC can last longer than the duration of the exercise
* Larger increase in ventilation
Low intensity, long duration exercise:
- Lower rate of energy expenditure
- Proportionally smaller oxygen debt
- Proportionally shorter duration and lower intensity of EPOC
How are our muscle stores replaced?
–> ATP stores are replaced by: making more ATP
–>Cr-P stores are replaced by: using ATP to regenerate Cr-P
Cr-P + ADP <–> Cr + ATP
–> Myoglobin: oxygen store restored
–> Lactic acid removed from muscle, into the blood, is used:
- By the liver to be converted into glucose via Cori cycle (uses 6 ATP)
- By other cells to be used to create more ATP (by converting it back into pyruvate)
E.g. lactate formed in ‘fast-twitch’ fibres is donated to ‘slow-twitch’ fibres to use for ATP production in the mitochondria
Respiratory responses to exercise?
Coordination of cardiovascular, respiratory, and cellular (ATP synthesis) systems
Fick principle?
- Originally used to measure cardiac output (expressed as Q or CO)
- Rearranged equation to determine oxygen consumption (VO2)
VO2 = Q (CaO2 - CvO2)
Ventilation during exercise - during steady-state low and moderate intensity exercise?
- Sudden increase in ventilation at exercise onset
- Feedforward response - Gradual increase until a steady-state is reached:
- When oxygen consumption (VO2) and carbon dioxide production (VCO2) are balanced with alveolar ventilation (VA), and ventilation plateaus - Sustained increase in ventilation for a period after the end of after exercise to replace O2 debt: EPOC
Ventilation during exercise - during steady-state low and moderate intensity exercise continued?
- Ventilation (VE) increases with exercise intensity
- Venous PO2 will decrease as exercise intensity increases because more O2 will be extracted from the systemic blood by exercising muscles (increased VO2) BUT:
- Arterial PO2 remains constant because the increase in oxygen consumption is matched by the increase in ventilation (VE) (more O2 is breathed in to replace the extra which has been used)
- Venous PCO2 will increase as exercise intensity increases because more CO2 is produced (increase in VCO2) by exercising muscles BUT:
- Arterial PCO2 remains constant because the increase CO2 production is matched by the increase in VE (the extra CO2 is breathed out)
- The arterial concentration of H+ remains constant because:
- The arterial PCO2 remains constant, so no extra H+ is made from CO2 AND
- Blood lactate/lactic acid concentration is low
Getting ready - during steady-state low and moderate intensity exercise?
Feedforward increase in ventilation immediately at the start of exercise
- Primary motor cortex
- Exercising muscle proprioceptors
Input from primary motor cortex and proprioceptors –> exercise ‘control command’ –> medullary respiratory centres –> respiratory system; increased ventilation
During - low/med intensity exercise?
Ventilation increases in proportion to exercise intensity
- Central and peripheral chemoreceptors (CO2)
- Muscle mechano- and chemo-receptors
- Increased core body temperature
- SNS: increased adrenaline
During exercise, ventilation is increased via input to:
- The respiratory system directly OR
- The medullary respiratory centres
Central and peripheral chemoreceptors (CO2) - during low/med intensity exercise?
During low-medium intensity exercise feedback from peripheral and central chemoreceptors increases ventilation to match the intensity of exercise:
- To remove more CO2 and maintain arterial PCO2
- (To provide more O2 and maintain arterial PO2)
Central and peripheral chemoreceptors respond to increased CO2 and decreased O2
Muscle mechano- and chemo-receptors - during low/med intensity exercise?
Muscle mechano- and chemo-receptors are activated by muscle contraction and metabolites:
- Feedback to the medullary respiratory centres
- Increases ventilation
Core body temperature - during low/med intensity exercise?
During exercise core body temperature increases:
- Feedback to the medullary respiratory centres
- Increases ventilation
