METABOLISM IN VARIOUS ORGANS OF VERTEBRATES

ORGAN	FUEL STORE	FUEL EXPORTED	NORMAL FUEL	FUEL IN STARVATION
BRAIN	none	none	glucose	ketone bodies (AcAc)
MUSCLE SKELETAL¹	glycogen	-lactate during activity -amino acids during starvation	-fatty acids under rest (aerobic) - glucose when active (anerobic)	ketone bodies
MUSCLE CARDIAC²	negligible	none	fatty acids glucose	ketone bodies
ADIPOSE TISSUE	TAG's	fatty acids and glycerol	fatty acids	.
LIVER	glycogen and TAG's	-TAG's in VLDL -glucose -ketone bodies	amino acids -glucose -fatty acids	amino acids

^1,2Skeletal and cardiac muscle differ significantly in function and fuel use. Skeletal muscles varies enormously in fuel needs based on activity and uses both aerobic and anerobic pathways. In contrast the heart activity is more constant, and it is completely aerobic. Also it has no energy reserves.