Plasma Glucose Homeostasis

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Plasma Glucose Homeostasis

• Glucose metabolism
• Hormonal Control
• Disruptions of glucose homeostasis
• Case Study

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Homeostasis of Plasma Glucose Concentration

• Normal physiological range 65-100 mg/dl
• Set point?
• Plasma glucose concentration glucose entering
  the plasma glucose leaving the plasma
• What are the mechanisms that regulate plasma
  glucose concentration?
• What are the components of the negative feedback
  loop
• Glucose receptors?
• Afferent pathway?
• Integrator?
• Efferent pathway(s)?
• Effector organ(s)?

Phasesabsorptive, post-absorptive, and
fasting
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Fig. 16.01
Lipoprotein Lipase
Absorptive Phase
Hepatic Portal System
Once inside, glucose is converted to something
else, thereby maintaining a concentration
gradientfor facilitated diffusion ofglucose
into cells.
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Fig. 16.02
Special case Muscle wasting of starvation
Glucose Sparing
Post-absorptive phase
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Major Points

• Absorptive phase lasts 4 hours
• During absorptive phase, energy needs provided by
  recently digested food
• During absorptive phase, excess is converted to
  stored fuel
• During post-absorptive phase, energy need met by
  release of stored fuels
• Fasting defined as greater than 12 hours after
  previous meal (some say 24 hrs)
• Fasting for several days has little effect on
  plasma glucose levels

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The Issues

• How do cells know which fuel to burn?
• How do cells know when to synthesize glycogen
  or lipids and when to break down glycogen or
  lipid?
• What is responsible for the transitions from the
  absorptive and post-absorptive states?

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Hepatic portal system
Alpha cells secrete glucagon Beta cells secrete
insulin Delta cells secrete somatostatin
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Peptide hormone

GLUT-4
Which cell types have insulin receptors?
T1DM beta cells fail to produce adequate insulin
(5) T2DM target cells resistant (less
responsive) to insulin
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Fig. 16.01
Absorptive Phase
Neurons dont have insulin receptors, but do
have Glucose transporters (not GLUT-4)
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(No Transcript)
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Fig. 16.04
Absorptive Phase
Post-Absorptive Phase
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Fig. 16.07
Identify sensors, afferent pathway,integrator,ef
ferent pathway,effectors
How is insulin secretion affected if plasma
glucose is lower than set point?