BIOC 462B: Dr' Tischler

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BIOC 462B Dr. Tischler
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GLUCOSE HOMEOSTASIS
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• Objectives
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• Identify the sources of blood glucose and the
  major fuel for the brain in the absorptive,
  postabsorptive, starvation and prolonged
  starvation states.
• Discuss how ketoacidosis (ketosis) is normally
  prevented in prolonged starvation.
• Discuss the role of the glucose/fatty acid/ketone
  body cycle in starvation.
• Discuss the roles of insulin, glucagon and
  cortisol in the pattern of changes in the major
  source(s) of fuel during the transition from the
  well-fed state to prolonged starvation.
• Describe how fatty acids help maintain blood
  glucose homeostasis in starvation.

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OVERVIEW OF SYSTEMS OF ENERGY METABOLISM
GLYCOGEN
TRIACYLGLYCEROLS
PROTEIN
Amino Acids
Glucose-6-P
Glucose
Free Fatty Acids
Lactate
Acetyl-CoA
Pyruvate
Ketone Bodies
CO2, H2O
ATP
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BLOOD GLUCOSE HOMEOSTASIS

• hyperglycemia too little insulin

• hypoglycemia too little intake or too much
  insulin

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Table 1 - Phases of glucose homeostasis
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fed postabsorptive gluconeogenic
prolonged I II
III
IV
40 30 20 10 0
Exogenous (glucose from diet)
glucose from gluconeogenesis (lactate amino
acids)
Glucose Used g/hr
glucose from gluconeogenesis (mostly lactate)
glucose from liver glycogen
4 8 12 16 2
7 42
HOURS
DAYS
Figure 1. Sources of blood glucose in the
various nutritional states
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Fuel Source ()
Well-fed state
Early Starvation 1- 5 days
Prolonged Starvation 7 days
NUTRITIONAL STATUS
Postabsorptive State 4-24 h
Figure 2. Changes in the major source of fuel
during the transition from well-fed state to
prolonged starvation.
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REVIEW
?-HBDH ?-hydroxybutyrate dehydrogenase
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Figure 3. Mechanism for prevention of
ketoacidosis from excess ketone body production
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Figure 4. The glucose\fatty acid cycle well
fed state
ADIPOSE TISSUE
BRAIN
CO2
Pyruvate
TG
insulin
GLC
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FA
Glucose
insulin
PANCREAS
BLOOD
GLUCOSE (diet)
FATTY ACIDS (diet)
GLC
Insulin
insulin
KETONE BODIES
GLC
CO2
MUSCLE
LIVER
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GLUCOSE UTILIZATION
Figure 5. Metabolic adaptation during the
gluconeogenic (early starvation) phase.
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Figure 6. The glucose\fatty acid\ketone body
cycle starvation
ADIPOSE TISSUE
BRAIN
CO2
TG
X
GLC
FA
PANCREAS
BLOOD
GLUCOSE
Insulin
FATTY ACIDS
MUSCLE
KETONE BODIES
GLC
FA
X
CO2
LIVER
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BLOOD GLUCOSE HOMEOSTASIS
Figure 7. Metabolic adaptation to prolonged
starvation. ? indicates increase and ? indicates
decrease of the process.