Feed-Fast Cycle

Question 1

what are the major metabolic functions of insulin

Answer 1

insulin is the major anabolic hormone of the body and promotes storage of fuel or used for growth

1. glycogenesis in liver and muscle
2. fatty acid and TAG synthesis in liver and release of VLDL
3. protein synthesis in muscle and liver (hepatic release of plasma proteins)

Question 2

what are the major metabolic functions of glucagon

Answer 2

Glucagon is the major hormone for fuel mobilization

1. hepatic glycogen degradation and gluconeogenesis leads to release of glucose into the blood
2. hepatic ketone body synthesis and release
3. TAG degradation in fat cells and release of fatty acids and glycerol (low insulin:glucagon ratio)

Question 3

describe the regulation (activation vs inhibition) of insulin release

Answer 3

• activation:
  
  • primary stimulus is rise in blood glucose
  • leucine and arginine enhance secretion
    
    • leucine because dietary essential, so only reason it’s in the body is because it was just eaten in meal
  • gastrointestinal peptide hormones increase the sensitivity of B-cells to glucose
• inhibition:
  
  • epinephrine

Question 4

How is blood glucose measured by B-cells and how does this result in insulin release?

Answer 4

• Glucose enteres B-cells using GLUT-2
• Glucokinase forms G6P
• Oxidative metabolism leads to ATP formation dependent on the amount of G6P
• blood glucose levels >5 mM generate a high level of ATP that close K+ channels
• Leads to depolarization of cell by Ca influx and leads to insulin release

Question 5

describe the regulation of glucagon secretion

Answer 5

• activation:
  
  • primary stimulus is a decrease in blood glucose
  • alanine and arginine enhance secretion
    
    • alanine can be turned into pyruvate
    • alanine allosterically inhibits hepatic pyruvate kinase
  • epinephrine stimulates glucagon release as it siginal physiologic stress
• inhibition:
  
  • elevated blood glucose levels and by insulin

Question 6

describe stress situations and how it affects regulation of insulin and glucagon

Answer 6

• under stress situations, the pituitary gland releases ACTH which stimulates release of cortisol
• cortisol is released from the adrenal cortex and stimulates the methylation of norepi and epi in the adrenal medulla
• epi inhibits insulin release from B-cells of pancreas and stimulates glucagon release from α-cells of pancreas

Question 7

describe the sources of blood glucose throughout a 24 fasting cycle

Answer 7

• Fasint gleads to release of glucose into the blood using: hepatic glycogen degradation and gluconeogenesis
• the liver glycogen stores decline after 6-8 hours and are empty after about 24 hours
• gluconeogenesis the only provider of blood glucose after 1 day. At that time, renal gluconeogenesis increases and both liver and kidney supply blood glucose

Question 8

describe the blood levels during 40 days of starvation

Answer 8