1. Plasma Glucose Homeostasis
Glucose metabolism
Hormonal Control
Disruptions of glucose homeostasis
Case Study

2. Homeostasis of Plasma Glucose Concentration
Normal physiological range: 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

3. Absorptive Phase Fig. 16.01 =sink Hepatic Portal System
Lipoprotein Lipase
Absorptive Phase
16.01.jpg
Hepatic Portal System
Once inside, glucose is converted to something else, thereby maintaining a concentration gradient for facilitated diffusion of glucose into cells.

4. Post-absorptive phase
Fig
Special case: Muscle wasting of starvation
Glucose Sparing
16.02.jpg
Post-absorptive phase

5. 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

6. 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?

7. Alpha cells secrete glucagon Beta cells secrete insulin
Hepatic portal system
Islets of Langerhans
Alpha cells secrete glucagon
Beta cells secrete insulin
Delta cells secrete somatostatin