Control of blood concentration

• How does adrenaline or glucagon act by a second messenger?


  The receptors for adrenaline/glucagon have specific tertiary structures that are complementary in shape

  This activates enzyme adenylate cyclase

  Adenylate cyclase converts ATP into cyclic AMP (cAMP)

  cAMP activates an enzyme called protein kinase A which activates a cascade

  Glycogenolysis occurs - break down of glycogen into glucose
• Cascade

  A chain of reactions
• Glycogenolysis

  Breakdown of glycogen into glucose
• Glycogenesis

  Synthesis of glycogen from glucose
• Beta cells

  Secrete insulin into blood
• Alpha cells

  Secrete glucagon into blood
• When does blood glucose concentration rise

  After eating food containing carbohydrates
• When does blood glucose concentration fall

  After exercise

  Glucose is used in respiration to release energy
• Which hormones control blood glucose concentration

  Glucagon and insulin
• What is an effector

  A targeted cell
• Where is insulin and glucagon secreted

  In the pancreas by the islets of Langerhans
• How is blood glucose concentration lowered when it's too high

  Pancreas detects blood glucose conc. is too high

  Beta cells secrete insulin and alpha cells stop secreting glucagon

  Insulin binds to specific receptors on the cell membrane of liver and muscle cells

  It increases the permeability of muscle cell membranes to glucose - by increasing the number of channel proteins

  Insulin activates enzymes which convert glucose into glycogen (glycogenesis)

  Cells store glycogen in cytoplasm

  Increases rate of respiration
• How is blood glucose concentration raised when it's too low

  Pancreas detects blood glucose conc. is too low

  Alpha cells secrete glucagon and beta cells stop secreting insulin

  Glucagon binds to specific receptors on the cell membranes of liver cells

  Glucagon activates enzymes to break down glycogen into glucose (glycogenolysis)

  Activates enzymes involved in the formation of glucose from glycerol and amino acids (gluconeogenesis)

  Glucagon decreases the rate of respiration
• Gluconeogenesis

  Formation of glucose from glycerol and amino acids or other non-carbs
• Why are hormones slower than nervous impulses

  Because they travel in the blood to their target cells
• Why are hormones more long lasting than nervous impulses

  Hormones are not broken down as quickly as neurotransmitters
• Channel protein found in skeletal and cardiac muscle

  GLUT4 - a glucose transporter
• Function of GLUT4 when insulin levels are low

  GLUT4 is stored in vesicles in the cytoplasm of cells

  When insulin binds to receptors on cell surface membrane - GLUT4 is triggered to move to the membrane and transport insulin into the cell using facilitated diffusion
• Adrenaline

  Hormone secreted from the adrenal glands
• When adrenaline binds to receptors on the cell membrane of liver cells, it...

  Activates glycogenolysis

  Inhibits glycogenesis

  Activates glucagon secretion
• Type 1 diabetes

  The immune system attacks beta cells found in the islets of Langerhans so they can't produce insulin

  Caused by genetic predisposition or a viral infection
• Hyperglycaemia

  When glucose levels rise and stay high after eating - can result in death if left untreated
• What happens to the excess glucose in a diabetic

  Can't be reabsorbed by kidneys

  Excreted in urine
• Insulin therapy

  Type 1 diabetics need regular insulin injections or insulin pumps
• Hypoglycaemia

  When blood glucose levels drop too low
• When is type 1 diabetes obtained

  Since birth
• Type 2 diabetes

  Acquired later in life

  Linked with obesity and unhealthy eating habits, family history or lack of exercise and age

  Occur when beta cells don't produce enough insulin or the body's cells don't response properly to insulin (dysfunctional insulin receptors)
• How can you reduce the risks of type 2 diabetes

  Eating a healthy and balanced diet

  Losing weight

  Regular exercise
• How is colorimetry used to determine the concentration of glucose solution

  High concentrations of glucose in urine can indicate diabetes

  Conduct a quantitative Benedict's test - when it's heated with glucose, the blue colour is lost but a brick-red precipitate is not produced

  A colorimeter measures the light absorbance of the solution after the test

  The higher the concentration of glucose, the more blue colour will be lost which decreases the absorbance of solution
• Practical


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