regulation of blood glucose

• the normal concentration of blood glucose is regulated carfeully, the normal range is between 4 and 6 mmol dm ^-3
• if one's blood glucose drops below 4 mmol dm^-3 for an extended period of time, they will be called hypoglycaemic.
• The main problem caused by hypoglycemia is an inadequate delivery of glucose to the body tissues, and in particular to the brain. Mild hypoglycemia may simply cause tiredness and irritability, however in more severe cases, there may be severe impairment of brain function and confusion- which may lead to seizures, unconsciousness and death.
• If blood glucose concentration is allowed to rise too high for long periods, the subject will be hypoglycemic. permanent high blood glucose can lead to significant organ damage. A blood glucose that is consistently higher than 7 mmol dm^-3 is considered to be used to diagnose diabetes mellitus.
• The cells in the islets of langerhans constantly monitor the concentration of glucose in the blood. If the concentration of blood glucose rises or falls away from the acceptable concentration then alpha and beta cells in the islets of langerhans detect the change and respond by releasing the relevant hormone. If the blood glucose is too high, then insulin is released. If the blood glucose is too low then glucagon is released.
• Insulin and Glucagon act on the hepatocytes which can store glucose in the form of glycogen. When there is excess glucose in the blood, it is converted glycogen. If glucose is needed to raise the blood concentration then glycogen is converted back to glucose.
• A high blood glucose concentration is detected by the beta cells in the islets of langerhans. The beta cells respond by secreting insulin into the blood. Insulin travels throughout the body in the circulatory system. The target cells are the liver, muscle and some other body cells including those in the brain.
• Human insulin is a small protein of 51 amino acids, therefore it is unable to pass through the cell surface membrane. The target cells possess the specific membrane-bound receptors for insulin. When insulin binds to the insulin receptor, this activates the enzyme tyrosine kinase which is associated with the receptor on the inside of the membrane. Tyrosine kinase causes phosphorylation of inactive enzymes in th ecell. This activates the enzymes leading to a cascade of enzyme-controlled reactions inside of the cell
• Insulin has several effects on the cell:

  
  

  More transporter proteins specific glucose are placed into the cell surface membrane. This achieved by causing vesicles containing transporter proteins to fuse with the membrane.

  More glucose enters the cell

  Glucose in the cell is converted glycogen for storage (glycogenesis)

  more glucose in converted to fats

  More glucose is used in respiration
• A low blood glucose concentration is detected by the alpha cells in the islet of langerhans. The alpha cells then secrete the hormone glucagon into the blood.
• Glucagon is a small protein containing 29 amino acid. Its target cells are the hepatocytes which possess the specific receptor for glucagon. WHen the blood passes these cells the glucagon binds to the receptors. This stimulates, a G protein inside the membrane this activates the adenyl cyclase inside each cell. The adenyl cylcase converts ATP into cAMP, which activates a series of enzyme controlled, reactions in the cell.
• What are effects of glucagon on the body?

  Glycogen is converted into gluce (glucogenolysis) by phosphorylase A, which is one of the enzymes activated in the cascade

  More fatty acids are used in respiration

  amino acids and fats are converted into additional glucose via gluconeogenesis