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Published byRosamond O’Neal’ Modified over 9 years ago
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Plasma Glucose Homeostasis Widmaier et al., p. 555-567
Glucose metabolism Hormonal Control Disruptions of glucose homeostasis A Case Study
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1QQ # 3 8:30 Section Which of the following are true during the absorptive phase? (Circle all correct responses.) Amino acids are taken up by muscle tissue. The liver converts glucose to a-ketoacids. Muscle cells polymerize glucose to glycogen. Excess amino acids are converted to triglycerides in the liver in a multi-stop enzymatic process As plasma glucose levels rise, so does the secretion of insulin. Adipose tissue converts excess glucose to triglycerides. Almost all cells use glucose as metabolic fuel. 1 a b c d e f g
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1QQ # 3 9:30 Section Which of the following are true during the absorptive phase? (Circle all correct responses.) Amino acids are released by muscle tissue. The liver converts glucose to a-ketoacids. Muscle cells polymerize glucose to glycogen. Excess amino acids are converted to triglycerides in the liver in a multi-stop enzymatic process As plasma glucose levels rise, secretion of insulin is diminished. Triglycerides enter adipose tissue cells. Almost all cells use fatty acids as their main metabolic fuel. 1 a b c d e f g
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Absorptive Phase Fig. 16.01 =sink Hepatic Portal System
Lipoprotein Lipase Absorptive Phase 16.01.jpg Hepatic Portal System
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Liver Hepatic portal system Alpha cells secrete glucagon
Typical vasculature: Artery-Arteriole-Capillary-Venule-Vein-Heart Islets of Langerhans Alpha cells secrete glucagon Beta cells secrete insulin Delta cells secrete somatostatin Hepatic portal system Artery-Arteriole-Capillary-Portal Vessel- Capillary-Venule-Vein-Heart Route of blood
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Post-absorptive phase
Fig Special case: Muscle wasting of starvation Glucose Sparing Special term: Glycogenolysis & Gluconeogenesis 16.02.jpg Post-absorptive phase Note: Nervous tissue can use glucose and ketones
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Major Points Absorptive phase lasts ~ 4 hours, cells “burn” glucose.
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, most cells “burn” fatty acids, nervous tissue uses glucose and ketones. 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? How does glucose get into “sink” cells?
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Which cell types have insulin receptors?
Fig Identify sensors, afferent pathway, integrator, efferent pathway, effectors How is insulin secretion affected if plasma glucose is lower than set point? 16.07.jpg Which cell types have insulin receptors?
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T1DM =beta cells fail to produce adequate insulin (5%)
Exercise (via an undescribed mechanism) increases the number of glucose transporters in muscle cell membrane Peptide hormone GLUT-4 Activates some enzymes, inactivates others ↑ 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
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Stimulatory actions of insulin in green
Inhibitory actions of insulin in dashed red
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Post-Absorptive Phase
16.04.jpg Post-Absorptive Phase
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? FF FF Glucose uptake, Storage, Lipogenesis
Thinking about food Factors that influence Insulin Secretion ? FF FF WHY? 16.08.jpg Glucose uptake, Storage, Lipogenesis The Integrator integrates multiple inputs
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Another hormone that regulates plasma glucose concentration
Glucagon prevails during post-absorptive phase 16.09.jpg Transition from absorptive to post-absorptive phase?
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Graph your daily caloric intake over a 48 hour period
Plasma Glucose 100 65 consumed Calories 6am Noon 6pm MN 6am Noon 6pm MN 6am Noon Overlay INSULIN SECRETION on the graph Overlay GLUCAGON SECRETION on the graph
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Glucose-counterregulatory controls (oppose effects of insulin)
Glucagon Epinephrine Cortisol (permissive effect) Growth hormone (permissive effect)
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Fig Don’t fret about receptors, afferent pathway, and integrator for this feedback loop. EPI, yet another horomone in glucose homeostasis, effects opposite of Insulin 16.10.jpg
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Who Cares?
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A Case Study On our website at
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.
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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 Sugar content of Red Bull?
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Hypoglycemia 60
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Stress, Emergency (fight or flight)
Effect on Alpha Cells Effect on Beta cells
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The Answer to the Problem?
Rationale for substituting protein for carbohydrate midnight snack?
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