Physiology Exam 2: Muscle Metabolism

ways muscles produce ATP

• creatine phosphate pathway

• anaerobic pathway (lactic acid fermentation

• aerobic cellular respiration

sources of glucose and FFAs in the body

• circulating in the blood

• storage forms

circulating in the blood

• glucose and free fatty acids travel in the blood

  • glucose and free fatty acids are transported into muscle cells

storage forms

• liver and skeletal muscle store glycogen

  • breaks down into glucose

  • glucose released into blood

• adipose tissue stores triglycerides

  • breaks down into fatty acids and glycerol

  • released into blood

creatine phosphate pathway

• reaction catalyszed by creatine kinase

  • enzyme found in skeletal, cardiac, and smooth muscle

• sufficient for short bursts of activity

  • ex) 100m dash

• for activities longer than 15 secs muscles need to metabolize nutrients to get ATP

• at rest reaction can reverse

anaerobic pathway (lactic acid fermentation)

• uses glucose but not free fatty acids

• provides enough energy for about 30-40 secs of maximal muscle activity

• 2 ATP per glucose

• skeletal muscle is the main tissue that utilizes this pathway

aerobic cellular respiration

• uses glucose and lipids

• requires oxygen

• 30-32 ATP per glucose

• glycolysis

• citric acid

• electron transport chain

glycolysis

• cytoplasm

• input: glucose

• output: pyruvic acid

citric acid

• mitochondria matrix

• input: pyruvic acid

• output: high energy electron storage molecules

electron transport chain

• mitochondria membrane

• input: electron transport chain

• output: ATP generation

• oxygen acceptor

oxygen

final electron acceptor

ketone bodies

• excess fat metabolism leads to this build up

• acidic; build up leads to acidosis

fatty acids and glycerol

• triglycerides stroed in cells can be broken down into these

• can be used to make ATP through aerobic respiration

keto acids

• this protein (amino acid) is the fuel used to make ATP

• can lead to acidosis

% of ATP derived from each pathway changes according to

• duration of activity

• activity intensity level

exercise duration increases (pathway)

% ATP produced aerobically increases

exercise intensity increases (pathway)

% ATP produced anaerobically increases

at rest (pathway)

ATP derived from aerobic pathway

at rest (muscles)

• 66% ATP from lipid metabolism

• 33% ATP from carbohydrate metabolism

beginning of exercise (muscle)

carbohydrate usage spikes

log duration, light to moderate exercise (muscle)

mix of carbohydrate and lipid metabolism

exercise intensity increase

• carbohydrate metabolism increases

• lipid metabolism decreases

2 main characterstics of muscle fibers

• speed of cxn (contraction)

• major pathway for forming ATP

slow fibers (slow twitch)

myosin heads split ATP more slowly

fast fibers (fast twitch)

myosin heads split ATP faster

oxidative fibers

• require nutrients

• rely on aerobic cellular respiration

• gluecose + FFAs

glycolytic fibers

• require nutrients

• rely on anaerobic glycolysis

• glucose onlyslow

slow oxidative

• primarily aerobic

• contain alot of myogobin and mitochondria

• reddish in color

• slowest to fatigue

• best suited for endurance activities (marathon running, maintaining posture)

fast glycolytic

• metabolize anaerobically

• low myoglobin content and few mitochondria

• white in color

• fast to fatigue

• best suited for “burst-type” activities that are short lived and powerful

muscle fatigue

• physiological inability to contract

• muscle can’t respond to stimulus

central fatigue

• feeling tired and wanting to stop activity

• originates in CNS

endurance exercise (skeletal muscle effect)

transforms some fast glycolytic into fast oxidative

weight training (skeletal muscle effect)

• increases size of fast glycolytic fibers

  • hypertrophy

  • mechanism

hypertrophy

increase in size of muscle/ muscle fibers

mechanism

increase in actin/myosin synthesis within fibers so fibers get bigger

atrophy

• loss of muscle mass due to disuse or injury

• but if nerve supply to muscles is intact and healthy, then this is reversible

glycogen

liver and skeletal muscle stores ___

triglycerides

adipose tissue stores ___