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Understanding Glucose Homeostasis: Source, Targets, and Feedback Loops

Explore the intricate mechanisms of glucose regulation with a focus on insulin, glucagon, and epinephrine. Learn about absorption phases, diabetes mellitus, renal glucose handling, and hormonal control. Dive into a case study and oral glucose tolerance test to deepen comprehension.

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Understanding Glucose Homeostasis: Source, Targets, and Feedback Loops

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  1. 17 September 2010 • 1QQ # 5 • Glucose Homeostasis • Source, targets, actions, negative feedback loops for • Insulin • Glucagon • Epinephrine • A case study in glucose homeostasis • Endocrinology: Begin Chapter 11 p 315-346 • Next week in lab: Reading a Research Paper • Scan the Androstenedione paper before coming to lab.

  2. 1QQ # 5a • Which of the following are true during the absorptive phase? (Circle all correct responses.) • Amino acids are released from muscle tissue. • The liver converts glucose to a-ketoacids. • Muscle cells generate glycogen from glucose • Excess amino acids are converted to triglycerides in the liver. • As plasma glucose levels rise, so does the secretion of insulin. • The main fuel molecules for most cells are fatty acids and ketones. • GLUT-4 transporters are inserted into the cell membranes of adipocytes. • 1 a b c d e f g

  3. 1QQ # 5b • Which of the following are true during the post absorptive phase? (Circle all correct responses.) • Amino acids are released from muscle tissue. • The liver converts glucose to a-ketoacids. • Muscle cells generate glycogen from glucose • Excess amino acids are converted to triglycerides in the liver. • As plasma glucose levels rise, so does the secretion of insulin. • The main fuel molecules for most cells are fatty acids and ketones. • GLUT-4 transporters are inserted into the cell membranes of adipocytes. • 1 a b c d e f g

  4. Activates some enzymes, inactivates others Recognize and distinguish between hyposecretion and hyporesponsiveness GLUT-4 ↑ plasma glucose →↑insulin secretion→↑glucose uptake into cells →↓ plasma glucose Diabetes mellitus: T1DM =beta cells fail to produce adequate insulin (5%) T2DM = target cells “resistant” (less responsive) to insulin Hyperglycemia

  5. Diagram of Kidney and renal “handling” of glucose Filtration Reabsorption Transport maximum (Tm) Explain how hyperglycemia Can result in glucose in the urine, and the consequences thereof. Analogy of Exceeding Transport Maximum: YouTube of Lucy at Candy Factory

  6. Fig. 16.07 Identify sensors, afferent pathway,integrator,efferent pathway,effectors How is insulin secretion affected if plasma glucose is lower than set point? Which cell types have insulin receptors?

  7. Stimulatory actions of insulin in green Inhibitory actions of insulin in dashed red

  8. Graph your daily caloric intake over a 48 hour period PlasmaGlucose 100 65 Calories consumed 6am Noon 6am 6am Noon MN Noon MN 6pm 6pm Overlay INSULIN SECRETION on the graph Overlay GLUCAGON SECRETION on the graph

  9. Absorptive Phase Post-Absorptive Phase

  10. ? Thinking about food Factors that influence Insulin Secretion FF FF WHY? Glucose uptake, Storage, Lipogenesis The Integrator integrates multiple inputs

  11. Another hormone that regulates plasma glucose concentration Glucagon prevails during post-absorptive phase Transition from absorptive to post-absorptive phase?

  12. Fig. 16.10 Don’t fret about receptors, afferent pathway, and integrator for this feedback loop. EPI, yet another horomone inglucose homeostasis, effects opposite of Insulin

  13. Glucose-counterregulatory controls (oppose effects of insulin) Glucagon Epinephrine Cortisol (permissive effect) Growth hormone (permissive effect)

  14. Who Cares?

  15. A Case Study • On our website at • http://webs.wofford.edu/davisgr/bio342/oggt.htm A Case Study of Glucose Homeostasis A 35 year old male presented with the following complaints: frequent severe headaches upon awakening at 4:30 am, blurred vision, and fatigue due to excessive stress at work. The patient complained of routine 16 hr workdays followed by a midnight snack of breakfast cereal. An OGTT was ordered and provided the following results: During the second hour of the OGTT, the patient exhibited anxiety, paleness, hunger, tremulousness, and cold sweat. No additional tests were ordered. The patient was instructed to replace the midnight snack of cereal with a protein-rich snack.

  16. Oral Glucose Tolerance Test • Overnight fast, no beverages other than water • Fasting blood sample • Ingest 75 grams glucose • Blood samples every 0.5 hours for 3-5 hours • Plot plasma glucose concentration over time • Compare curves

  17. 60 Hypoglycemia

  18. Stress,Emergency (fight or flight) Effect on Alpha Cells Effect on Beta cells

  19. The Answer to the Problem? • Rationale for substituting protein for carbohydrate midnight snack?

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