Control of BG Concentration

• If blood glucose concentration becomes too high, this will lower the water potential of the blood; water will then move out of cells, by osmosis. Causing them to shrivel and die.
• If blood glucose is too low, there will be insufficient respiration occurring so the cells will lack ATP and be unable to complete their normal metabolic processes.
• Glucose - a monosaccharide, the main respiratory substrate
• Glycogen - a polysaccharide, made up of alpha glucose joined by glucosidic bonds
• Glucagon and Insulin - hormones used to regulate blood glucose concentration
• Glycogenesis - conversion of glucose molecules into glycogen
• Glyconeogenesis - conversion of amino acids and glycerol into glucose
• Glycogenolysis - the hydrolysis of glycogen into glucose
• Blood glucose concentration is regulated by the Islets of Langerhans which is a tissue in the pancreas
• Alpha Cells - have receptors which detect a decrease in BG concentration and secrete the hormone glucagon
• Beta Cells - have receptors which detect the increase in BG concentration and secrete the hormone insulin
• The action of insulin:

  • the attaching to the receptors on the surfaces of target cells
  • controlling the uptake of glucose by regulating the inclusion of channel proteins in the surface membranes of the target cells
  • activating enzymes involved in the conversion of glucose to glycogen - this maintains the concentration gradient so glucose diffuses into the cells
• The action of glucagon by...

  • attaching to receptors on the surface of target cells e.g. liver cells and activating enzymes involved in the conversion of glycerol and amino acids into glucose.
• Glycogenolysis:

  • glucagon or adrenaline bind to receptors on liver cell
  • the receptor changes shape and activates the enzymes adenylate cyclase
  • adenylate cyclase converts ATP -> cAMP
  • cAMP is the second messenger and activates protein kinase
  • protein kinase hydrolyses glycogen into glucose
• Type 1:

  • Diagnosed early in life, thought to be an autoimmune disease caused by infection with a virus.
  • The beta cells are destroyed as no insulin is produced.
  • Regulation is by taking regular insulin injections and via diet.
• Type 2:

  • Diagnosed later in life, as it tends to develop due to poor diet - obesity
  • The beta cells produce less insulin or the receptors on the target cells become desensitised to insulin.
  • Regulation is via diet/exercise and sometimes insulin injections