Carbohydrate metabolism Flashcards
Creatine phosphate
First top up source for muscle ATP
At rest muscle has 100mmol PCr per dry kg weight- lasts 16 seconds
May be enough for 1-200m
Characteristics of skeletal muscle blood flow
20% cardiac output at rest, increases more than 80% extreme exertion
Coordinated, rhythmical contractions enhance blood flow by skeletal muscle pump
Vascular B2-adrenoreceptors result in vasodilation, stimulated by agonists such as adrenaline
Energy metabolism during exercise
Glycogenolysis provides fuel source
Increase in O2 consumption for ox phos
Increased blood flow to muscles due to local mediators and B-adrenergic stimulation of vascular smooth muscles
Amount of energy derived from glycolysis and respiration dependent on the intensity and duration of the exercise
The Cori Cycle
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, lactic acid builds up in the muscle
Fatigue
Inability to maintain desired power output
Occurs when rate of ATP utilisation exceeds its rate of synthesis
Accumulation of pyruvate and lactic acid in the contracting muscle result in a decline in force generated
Due to decrease in muscle pH
Regulation of glycogen metabolism
Glycogen breakdown and glycolysis are greatly stimulated during contraction
Muscle contraction is associated with increase in Ca2+concentration within the muscle cells
Increase in Ca2+ activates glycogen phosphorylase
The role of Ca2+ in muscle contraction
Increase in Ca2_ concentration is the signal for muscle contraction
Also increases muscle glycogen breakdown to supply the energy required
Stimulates the production of nitric oxide which causes vasodilation of the blood vessels and increased blood flow
Energy metabolism during exercise
In addition to glycogen, muscle also uses fatty acids derived from the diet or adipose tissue to maintain ATP levels
Fatty acid oxidation is aerobic and dependent on an adequate oxygen supply
Resting muscle metabolism
In resting muscle, glycogen stores are maintained/ replenished
Oxidative metabolism of fatty acids provides energy for the muscle
Energy utilisation during exercise
Only 2 fuels are used in short sprints: phosphocreatine and anaerobic glycogen breakdown
As distance increases, PCr exhausted, relies solely on glycogen breakdown aerobically or anaerobically
During the marathon, muscles reliant entirely on oxidative metabolism of glycogen, glucose and fatty acids
Metabolism whilst sprinting
Catecholamines stimulate glycogen breakdown, converted anaerobically to lactate
Phosphocreatine onverted to creatine and ADP goes to ATP
Blood vessels compressed during sprinting isolating cells, makes muscles reliant on anaerobic energy production
Large quantities of lactic acid produced as glycolysis proceeds which the liver can use to maintain blood glucose levels via gluconeogenesis
Middle distance metabolism
Aerobic oxidation makes up 30% ATP required to support contraction
Lactate still major end product of glycogen metabolism contributing 65% ATP required
Marathon stage 1
In resting muscle and liver, glycogen stores are maintained
Muscle uses aerobic oxidation of fatty acids to provide the energy it requires
Marathon stage 2
10 minutes
Muscle glycogen and glucose from liver used to power muscles, mainly through glycolysis
Increased vasodilation in muscles increases O2 supply increasing aerobic glycogen utilisation and ATP production
Fatty acids are mobilised by the release of adrenaline to allow liver to maintain blood glucose levels by the provision of energy and the glycerol backbone
Marathon stage 3
2 hours
Blood glucose falls significantly, about 90% lier glycogen used
Body switches to fatty acids as main source of energy
Ketone bodies also used
Lactate, glycerol and muscle amino acids used to support glucose production by the liver, energy being derived from fatty acid oxidation
