CIE IGCSE Biology: 复习笔记：14.1.8 Homeostasis: Definition

• Homeostasis is defined as the maintenance of a constant internal environment

• Homeostasis means that internal conditions within the body (such as temperature, blood pressure, water concentration, glucose concentration etc) need to be kept within set limits in order to ensure that reactions in body cells can function and therefore the organism as a whole can live
• When one of these conditions deviates far away from the normal if not brought back within set limits the body will not function properly and the eventual consequence without medical intervention will be death

The Role of Insulin

• Insulin is secreted into the blood at times when blood glucose levels are high
• This is (most often) directly after a meal
• The kidneys can only cope with a certain level of glucose in the blood
  • If the level gets too high, glucose gets excreted and is lost in the urine
  • This is like running a car with a hole in the petrol tank; valuable fuel is being wasted
• To avoid this, insulin temporarily converts excess glucose into glycogen in the liver and muscles
  • Insulin decreases blood glucose concentration
• The glycogen is converted back to glucose several hours later when blood glucose levels have dipped due to respiration in all tissues

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