• Normal Blood glucose concentration: 90 mg/100cm-3
  • Monitored by the pancreas
  • Increases due to consumption of carbohydrates
  • Decreases due to exercise

Hormonal Control of Blood Glucose Concentration

  • Blood glucose concentration is the result of the hormones insulin and glucagon
  • Insulin and glucagon are secreted by islet of Langerhans found in the pancreas.
  • 2 types Islet of Langerhans
    • Alpha Cells
      • Secretes glucagon into the blood
    • Beta cells
      • Secretes insulin into the blood

Insulin

  • Lower blood glucoses concentrations (when too high)
  • Binds to specific receptors on cell membranes on muscle cells and hepatocytes (liver cells)
  • Increases permeability of muscle-cell membranes to glucose so that the cells take up more glucose
    • It does this by increasing the number of channel proteins on the cell membrane
  • Glycogenesis is the activation of an enzyme in muscle and liver cells that convert glucose à glycogen
    • Cells are able to store glycogen in cytoplasm

Glucagon

  • Raises blood glucose concentration (when too low)
  • Binds to specific rececptors on the cell membrane of liver cells
  • Glycogenolysis is the activation of an enzyme that break down Glycogen à Glucose

  • Gluconeogenesis is the activation of a different enzyme which is involved in the formation of glucose from glycerol and amino acids

Overall Process of glycogenolysis and gluconeogenesis

Rise in Glucose Blood Concentration

  • Pancreas detect blood glucose concentration is too high
  • Beta cells secrete insulin and the alpha cells stop secreting glucagon
  • Insulin binds to receptors on liver and muscle cells
  • Liver and muscle cells respond to decrease the blood glucose concentration (glycogenesis)
  • Blood glucose concentrations return back to normal

Fall In Glucose Blood Concentration

  • Pancreas detect blood glucose concentration is too low
  • alpha cells secrete glucagon and beta cells stop secreting insulin
  • Glucagon binds to receptors on liver
  • Liver respond to increase the blood glucose concentration (glycogenolysis)
  • Blood glucose concentrations return back to normal

Glucose Transporters

  • Type of channel protein
  • Allows glucose to be transported across cell membrane
  • Skeletal and cardiac muscles contain a type of glucose transporter (GLUT4)
  • Insulin levels are low:
    • GLUT4 is stored in vesicles in the cytoplasm
  • Insulin Levels are high:
    • GLUT4 moves to the cell membrane
    • Glucose can be transported into the cell using the GLUT4 protein via facilitated diffusion

Adrenaline

  • A hormone that is secreted from the adrenal gland (kidneys)
  • Secreted when low concentration of glucose in blood during stressed activity
  • Adrenaline binds to receptors on cell membrane of liver cells to:
    • Activates glycogenolysis
    • Inhibits glycogenesis
    • Activates glucagon secretion
    • Inhibitors insulin secretion
  • Overall adrenaline increase the glucose concentration for muscle response
  • Type of second messenger
    • Both adrenaline and glucagon activate glycogenolysis inside a cell despite there only being binding to receptors on the outside of the cell
    • Second messenger model is the binding of the hormone to cell receptors which activate an enzyme on the inside of the cell membrane which bring about a response