regulation of blood glucose concentration

• what is glycogenolysis?

  when glycogen in the liver is broken down into glucose
• what is gluconeogenesis?

  production of glucose from non-carbohydrate sources- eg liver making glucose from glycerol and AAs.
• what is glycogenesis?

  production of glycogen
• what happens when blood sugar is too high?

  • beta cells in the pancreas detect the blood glucose levels and secrete insulin directly into the bloodstream
  • insulin binds to glycoprotein receptor, causing change in tertiary structure of glucose transport protein channels
  • channels open allowing more glucose to enter the cell
  • insulin activates enzymes within cells to convert glucose into glycogen and fat
  • in turn this lowers the glucose concentration in the blood (blood glucose concentration)
• in what ways throughout the body does insulin lower blood glucose concentration?

  • increases rate of absorption of glucose by cells
  • increases respiratory rate of cells so they have a higher demand for glucose
  • increases rate of glycogenesis
  • increases rate of glucose to fat and glycogen conversion in cells
  • inhibits release of glucagon from alpha cells from IOL
• how is insulin broken down and how does insulin maintain its affect in the bloodstream?

  • broken down by enzymes in liver cells
  • so must be secreted constantly
• true or false- all cells have glucagon receptors

  FALSE- only liver and fat cells
• true or false- almost all cells have insulin receptors

  TRUE- except erythrocytes
• in what ways does glucagon raise blood sugar concentration throughout the body?

  • glycogenolysis
  • reducing amount of glucose absorbed by liver cells
  • increases gluconeogenesis- conversion of AAs and glycerol into glucose
• how do insulin and glucagon work together to maintain constant blood glucose concentration?

  • they are antagonistic - system is self regulating- the level of glucose in the blood determines quantity of insulin and glucagon released
  • negative feedback- when blood glucose is too high/low etc

  
• describe the mechanism of the control of insulin secretion

  • at normal [blood glucose]- K ion channels are open in plasma membranes of beta cells (-70mv) resting potential
  • when blood glucose levels rise, glucose enters cell via glucose transporter
  • glucose metabolised in mitochondria, ATP is produced
  • ATP binds to potassium channels and causes them to close
  • potassium ions can't diffuse out, so depolarisation occurs and the membrane goes to -30mV
  • calcium ion channels open and Ca ions enter, causing secretory vesicles to release insulin they contain by exocytosis

  
• state the ways in which blood glucose concentration in the blood can be lowered and raised

  LOWERED-

  • respiration- glucose in blood is used by cells to release energy
  • glycogenesis- glucose converted into glycogen in the liver

  RAISED-

  • diet- eating carbohydrate rich food- these carbs are broken down into glucose which is absorbed into the bloodstream, increasing blood glucose concentration
  • gluconeogenesis- production of glucose from non-carbohydrate sources- glycerol and amino acids
  • glycogenolysis- breakdown of glycogen into glucose, glucose released into bloodstream
• describe how negative feedback ensures that blood glucose levels are regulated by beta cells

  when blood glucose concentration falls below a set level, beta cells decrease their insulin secretion- this is an example of negative feedback, allowing glucose concentration to rise to more optimal levels
• describe how negative feedback ensures that blood glucose levels are regulated by alpha cells


  • alpha cells detect that blood glucose concentration is above a certain level
  • therefore they reduce their secretion of glucagon- this is an example of negative feedback
• true or false? blood glucose concentration is constant

  FALSE- fluctuates around a certain level because of negative feedback