Feed Fast Cycle Flashcards
How is metabolic homeostasis achieved?
Normal cell functions require a constant source of fuels regardless of food intake or fasting/starvation
Metabolic homeostasis in tissues results from the balance between
- storage of energy
- mobilization of stored energy
This is achieved with communication by:
- Blood with hormones or substrates
- Nervous
Describe the general metabolic functions of insulin
Insulin is the major anabolic hormone and promotes storage of fuel or usage for growth
- Glycogenesis in liver and muscle
- fatty acid and TAG synthesis in liver (release of VLDL)
- protein synthesis in muscle and liver (serum proteins )
What are the general metabolic functions of glucagon?
Glucagon is a major hormone for fuel immobilization
- Hepatic glycogen degradation and gluconeogenesis.
- Hepatic ketone body synthesis and release
- Low insulin/glucagon ratio in blood leads to TAG degradation in fat cells and to release of fat acids and glycerol
What does insulin activate generally?
- glycolysis
- glycogen synthesis
- protein synthesis
- synthesis of fatty acids
- synthesis of cholesterol
What does glucagon activate generally?
- Gluconeogenesis
- Glycogen degradation
- usage of amino acids for gluconeogenesis
- degradation of fatty acids
- synthesis of ketone bodies
Give the general time frame of the feed state
The postprandial (absorptive ) phase is the time of the feed state with ongoing digestion and absorption after a meal (prandi) which is approximately 2 hrs after food intake
What is the general time frame of the fasting state?
The post-absorptive phase is the time of the fasting where the food is completely digested and absorbed which is approximately 5 hrs after a meal or the time after an overnight fast
Describe the early phase of starvation
Early phase of starvation starts about 3 days after last food intake. The time after 10 days of fasting/starvation can be seen as prolonged starvation
What are the blood levels of insulin and glucagon after a glucose rich meal?
- Post-prandial increase of glucose leads to increase of insulin and decrease glucagon
- the insulin-glucagon ratio is high
- Note: the glucagon level drops only 25% and is ready to be raised during fasting
How does the liver play a central role in reducing the rise of blood glucose after a meal?
- the liver receives blood from the portal vein containing dietary monosaccharides and insulin
- Insulin assures that sugars are trapped inside of the hepatocytes to reduce the rise of postprandial blood glucose levels and to support blood glucose homeostasis.
At very high blood glucose levels following extensive glycolysis, insulin stimulates the hepatic synthesis of fatty acids, TAGs and cholesterol. VLDLs are released into the blood
Explain glucose uptake by insulin-dependent glucose transporters
GLUT-4 are mainly found in fat tissue and muscle
- Insulin binds to its receptor in the cell membrane
- Binding causes a signaling cascade that promotes recruitment of glucose transporters from intracellular pool to cell membrane
- GLUT-4s increase insulin-mediated uptake of glucose into the cell
- When insulin levels decrease, GLUT 4s move from the cell membrane to the intracellular storage pool, where they can be recycled
- Vesicles fuse to from an organelle called the endosome
Explain the general postprandial adipose tissue metabolism
After a meal insulin activates lipoprotein lipase in capillaries of adipose tissue and GLUT-4 transporters in the fat cell plasma membrane. Inside of fat cells insulin stimulates TAG synthesis
Lipoprotein generates free fatty acids
Glycerol 3-p from glycosidic and free fatty acids used for TAG synthesis and storage
Describe postprandial muscle metabolism
High insulin levels
Insulin activates glucose uptake from blood (via GLUT-4) glycogen synthesis and glycolysis take place
Insulin activates amino acid uptake from the blood.
Protein synthesis is stimulated especially by leucine
Usage of branched-chain amino acids for protein synthesis and for energy metabolism
How does availability of substrates from the blood determine the pathways of liver, muscle and fat?
High levels of blood glucose after a meal:
Liver: glycolysis, synthesis of glycogen, fatty acids, TAGs, cholesterol and VLDL
Muscle: glycolysis and glycogen synthesis
Fat cells: glycolysis and TAG synthesis
High levels of blood free fatty acids during fasting:
Liver: B-oxidation of fatty acids and ketone body synthesis
Muscle: B-oxidation of fatty acids and ketone body usage
How does the liver regulate blood glucose AFTER A MEAL?
Uptake of dietary sugars reduces increase of blood glucose
Pathways: insulin stimulates hepatic :
- Glycogen synthesis
- Fatty acid synthesis
- Cholesterol synthesis
