The Feed/Fast Cycle

Question 0

In the absence of food, plasma levels of glucose, amino acids and TAG fall, causing a ⬇️ insulin and ⬆️ glucagon and ⬆️ epinephrine

The INSULIN: glucagon ratio and the ⬇️ availability of circulating substances make this period a CATABOLIC PERIOD

Answer 0

FASTING STATE

Question 1

2-4 hour period after ingestion of a normal meal

During this interval, transient increases in plasma glucose, amino acid, and triacylglycerols occurs

The PANCREAS respond to elevated levels of glucose and amino acids by ⬆️ insulin and ⬇️ glucagon secretion

The INSULIN: glucagon ratio makes the absorptive state an ANABOLIC PERIOD

Answer 1

ABSORPTIVE/FEED STATE

Question 2

Virtually all tissues: use GLUCOSE as fuel

Liver: replenishes its glycogen stores, replaces any needed hepatic proteins and ⬆️ TAG synthesis (lipolysis fat)

Adipose: ⬆️ TAG synthesis and storage

Muscle: ⬆️ protein synthesis

Brain: uses GLUCOSE EXCLUSIVELY as fuel

Answer 2

FED STATE

Question 3

Liver: degrades GLYCOGEN, initiates gluconeogenesis, using ⬆️ FA oxidation both as a source of energy and to supply the acetyl VoA building blocks for ketone body synthesis

Adipose: degrades stored TAG, thus providing FA and glycerol to the liver

Muscle: can also use FA as wells as ketone bodies; protein is degraded to supply AA for the liver in gluconeogenesis

Brain: uses glucose and, during a prolonged fast, KETONE BODIES

Answer 3

FASTING STATE