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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?
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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)? Phases:*absorptive, *post-absorptive, and fasting
=sink Fig. 16.01 Absorptive Phase
Fig. 16.02 Glucose Sparing Post-absorptive phase
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
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?
Activates some enzymes, inactivates others Which cell types have insulin receptors?
=sink Fig. 16.01 Absorptive Phase Neurons don’t have insulin receptors, but do have Glucose transporters
Fig. 16.04 Absorptive Phase Post-Absorptive Phase
Fig. 16.07 Id sensors, afferent pathway,integrator,efferent pathway,effectors How is insulin secretion affected if plasma glucose is lower than set point?