Lab 17: Glucose Tolerance

Role of Pancreas in Regulation of Blood Glucose:

  • fasting causes decreases glucose

    • Sensor & Integrating Center: Pancreatic islets monitor blood glucose

      • sense an decrease of glucose and cause:

        • beta cells in pancreatic islets to decrease insulin secretion

        • alpha cells in pancreatic islets to increases glucagon secretion

    • Effectors: Skeletal muscle, liver cells, and adipocytes

      • increase in glucagon stimulates:

        • causes Glycogenolysis in the liver, releasing glucose into the blood

        • promotes gluconeogenesis in liver (the production of glucose from non-carbohydrate sources), to make up for low glucose levels

          • increases plasma concentration

      • decrease in insulin causes removal of glucose transporters in liver and muscle cells

        • causes Glycogenolysis in skeletal muscle cells only (hydrolysis of glycogen into glucose)

        • also promotes ketogenesis (formation of ketone bodies from fatty acids)

        • also promotes hydrolysis of fat and protein

          • hydrolysis of glycogen, fat, and protein causes changes in blood levels:

            • increase in blood glucose

            • increase in amino acids in blood

            • increase in fatty acids in blood

            • increase in ketone bodies

  • absorption of a meal increase glucose

    • Sensor & Integrating Center: Pancreatic islets monitor blood glucose

      • sense an increase of glucose and cause increase in beta cells secretion and decrease in alpha cells secretion

        • beta cells in pancreatic islets increases insulin secretion

        • alpha cells in pancreatic islets to decreases glucagon secretion

          • hormones (insulin and glucagon) are just messengers

    • Effectors: Skeletal muscle, liver cells, and adipocytes

      • increase in insulin and decrease in glucagon causes insertion of glucose transporters in liver and muscle cells

        • promotes glucose uptake by tissues, forming glycogen to be stored in liver and skeletal muscle, promoting glycogenesis

          • if run out of space for glycogen storage, promotes formation of fat, and protein

            • promotion of glycogen, fat, and protein causes changes in blood levels:

              • decrease in blood glucose

                • due to glycogen being stored in liver and skeletal muscle

              • decrease in amino acids in blood

                • due to formation of protein

              • decrease in fatty acids in blood

                • due to formation of fat

              • decrease in ketone bodies

Diabetes Mellitus

  • Diabetes Mellitus: disease where body either does not produce enough insulin or does not respond adequately to insulin, resulting in abnormally high blood glucose levels

    • Type 1 Diabetes Mellitus: pancreas secretes little to no insulin in response to glucose load

    • Type 2 Diabetes Mellitus: tissue no longer responds adequately to circulating insulin

      • glucose tolerance test: help diagnose type 1 and type 2 diabetes and examines how well body responds to glucose load, demonstrating negative feedback loop for glucose levels

        • in lab, examine homeostatic regulation of blood sugar levels in normal fasted individuals

          • expected results:

            • after ingesting glucose, significant increase in blood glucose

            • followed by return to baseline

      • Possible Errors to Experiment:

        • subjects did not fast

        • malfunction with equipment

        • errors made by experimenters

  • Diabetes insipidus: disease characterized by failure of posterior pituitary to produce ADH, resulting in inadequate reabsorption of water by kindeys and production of copious amounts of urine

Definitions:

  • glycogenesis: generations of glycogen from glucose, stimulated by insulin

  • gluconeogenesis: generation of glucose from non-carbohydrate molecules such as amino acids and lactic acid

  • glycogenolysis: hydrolysis of glycogen to glucose

  • ketone bodies: substance derived from fatty acids and used as fuel by muscle and brain

  • ketoacidosis: type of metabolic acidosis caused by excessive production of ketone bodies