T2 L9 Energy metabolism during exercise Flashcards
How much can muscle increase its rate of ATP production in the short term?
By 20-100 fold
How much ATP does the muscle have at rest?
27mmol of ATP per kg dry weight
During vigorous contraction this lasts for 4 seconds
List the 3 systems that form ATP in muscle from fastest to slowest
ATP-PC
Lactic acid - glycolysis
Oxygen system - oxidative phosphorylation
What is the fuel used by the ATP-PC system?
Phosphocreatine
What is the fuel used by the lactic acid (glycolysis) system?
Glycogen
What is the fuel used by the oxygen system (oxidative phosphorylation)?
Glycogen
Fats
Proteins
O2 is required
List the 3 systems that form ATP in muscle from the most ATP produced to the least.
Oxygen system - many, unlimited ATP
Lactic acid
ATP-PC
What is creatine phosphate?
First top up source for muscle ATP
Creatine can be reversible phosphorylated to create creatine phosphate
Creatine phosphate breaks down to form creatinine which is excreted in the urine
How much creatine phosphate is stored in the muscle at rest?
Muscle has 100mmol creatine phosphate per kg dry
Lasts for 16 seconds so may be enough for 100-200m sprint
Skeletal muscle accounts for how much of cardiac output at rest and during vigorous exercise?
20% at rest
80% during extreme physical exertion
What are vascular beta 2 adrenoceptors?
Stimulated by agonists such as adrenaline which leads to vasodilation
What factors determine blood flow?
Local regulatory factors Tissue hypoxia Adenosine K+ CO2 H+ Nitric oxide
What increases blood flow to muscles during energy metabolism during exercise?
Local mediators - nitric oxide
Beta-adrenergic stimulation of vascular smooth muscle
What is the amount of energy derived from glucose & respiration dependent on?
The intensity & duration of exercise
What happens if the rate of metabolism exceeds the oxygen supply?
Glycolysis occurs anaerobically
Much less ATP is produced & lactate builds up
What causes an accumulation of lactate when oxygen supply is plentiful?
Pyruvate is formed faster than it can be oxidised which causes an accumulation of lactate
Why does lactic acid decrease pH?
It dissociates into a lactate ion & protein at a physiological pH which decreases pH
What is the Cori cycle?
Pathway where lactate is used by the liver to regenerate glucose which is transferred back t the muscle for energy production.
What is fatigue?
Inability to maintain desired power output
Occurs when the rate of ATP utilisation exceeds its rate of synthesis
Accumulation of pyruvate & lactic acid in the contracting muscle lead to a decline in the force generated.
What does an increase in calcium ions do to glycogen phosphorylase?
It activates it.
What is the role of calcium ions in muscle contraction?
The increase in Ca2+ concentration signals muscle contraction & increases muscle glycogen breakdown to supply the energy required.
Stimulates production of nitric oxide which causes vasodilation of blood vessels & increased blood flow
How is phosphorylase activated?
By AMP which acts allosterically
Activated by phosphorylation in response to a stress hormones, increased cytoplasmic calcium ions.
How is glycogen synthase activated?
Allosterically by glucose-6-phosphate which is low during exercise
How is glycogen synthase inactivated?
By phosphorylation in response to stress hormones, increased calcium ions
How is phosphofructokinase-1 inhibited?
Allosterically by ATP & activated by AMP & Fru-2,6-P
Important sensor of energy availability & needs during exercise
What are the 2 fuels used in short sprints to replenish ATP?
Phosphocreatine
Anaerobic glycogen breakdown to lactate
What does the muscle rely on as distance increases & phosphocreatine levels are exhausted?
Glycogen breakdown anaerobically or aerobically via TCA cycle.
What are the muscles reliant on during a marathon?
Oxidative metabolism of glycogen, glucose & fatty acids from the liver & adipose tissue.
Describe metabolism whilst sprinting
Catecholamines stimulate glycogen breakdown in muscle which is anaerobically converted to lactate. Phosphocreatine is converted to creatine with transfer of Pi to ADP to form ATP
Blood vessels are compressed which isolates cells from blood supply. Makes muscles reliant on anaerobic energy production from glycogen.
Large quantities of lactic acid are produced as glycolysis excess what the liver can use to maintain blood glucose levels via gluconeogenesis.
Describe metabolism for middle distance
Aerobic oxidation of glycogen makes up 30% of ATP required to support contraction. Some of oxygen may come from oxymyoglobin in the muscle.
Lactate is still a major end product of glycogen metabolism - contributes 65% of the ATP required.
Contribution of phosphocreatine to ATP required becomes less as distance increases.
Describe stage 1 of a marathon
In the resting muscle & liver the glycogen stores are maintained.
Muscle uses aerobic oxidation of fatty acids to provide the energy it requires.
Describe stage 2 of a marathon
First 10 minutes
Muscle glycogen & glucose from the liver are used to power muscles mainly through glycolysis.
Increased vasodilation in the muscles increases oxygen supply, which increases aerobic glycogen utilisation & ATP production.
Glycogen breakdown is stimulated by increased AMP & adrenaline release
Fatty acids are mobilised by the release of adrenaline to allow the liver to maintain blood glucose levels by provision of energy & glycerol backbone.
Describe stage 3 of a marathon
After 2 hours
Blood glucose falls as 90% of liver glycogen is used
Insulin levels fall & glucagon secretion increases.
Body switches to fatty acids as the main source of energy - only generates enough ATP for 50% of maximum power output.
Lactate, glycerol & muscle amino acids are used to support glucose production by the liver.
How much glycogen does a marathon require?
700g
Muscle & liver contain 500g which runs out after 20 miles
Describe stage 4 of a marathon
Finish
Muscle & liver glycogen are depleted
Hypoglycaemia - less likely to with training.
What are the symptoms of hypoglycaemia?
Confusion
Lack of cognitive function
Lactic acidosis
Exhaustion
