Homeostasis of Plasma Glucose Concentration

1. 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

2. =sink Fig. 16.01 Absorptive Phase

3. Fig. 16.02 Glucose Sparing Post-absorptive phase

4. 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

5. 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?

6. Islets of Langerhans

7. Activates some enzymes, inactivates others Which cell types have insulin receptors?

8. =sink Fig. 16.01 Absorptive Phase Neurons don’t have insulin receptors, but do have Glucose transporters

10. Fig. 16.04 Absorptive Phase Post-Absorptive Phase

11. Fig. 16.07 Id sensors, afferent pathway,integrator,efferent pathway,effectors How is insulin secretion affected if plasma glucose is lower than set point?