CIE IGCSE Biology

Revision Notes

14.2.2 Homeostasis: Blood Glucose

Homeostasis: Basics

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

  • This means that internal conditions within your 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
  • This is why diabetics need to control glucose intake (as their body cannot regulate it for them), why an extremely high and prolonged fever will kill you or why drinking too little or too much water can damage cells throughout the body – especially the kidneys and brain – and lead to death within days
  • Most homeostatic mechanisms in the body are controlled by a process known as negative feedback
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Negative Feedback

  • Negative feedback occurs when conditions change from the ideal or set point and returns conditions to this set point
  • It works in the following way:
    • if the level of something rises, control systems are switched on to reduce it again
    • if the level of something falls, control systems are switched on to raise it again
  • Negative feedback mechanisms are usually a continuous cycle of bringing levels down and then bringing them back up so that overall, they stay within a narrow range of what is considered ‘normal

The negative feedback cycle, IGCSE & GCSE Biology revision notesThe negative feedback cycle

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Control of Blood Glucose Levels

  • Blood glucose levels are controlled by a negative feedback mechanism involving the production of two hormonesinsulin and glucagon
  • Both hormones which control blood glucose concentration are made in the pancreas
  • Insulin is produced when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored
  • Glucagon is produced when blood glucose falls and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood

Negative feedback regulation of blood glucose levels, IGCSE & GCSE Biology revision notesNegative feedback regulation of blood glucose levels

Exam Tip

The terms glucagon and glycogen are very often mixed up by students as they sound similar. Remember: 

  • Glucagon is the hormone
  • Glycogen is the polysaccharide glucose is stored as

Learn the differences between the spellings and what each one does so you do not get confused in the exam!

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Diabetes

  • Type 1 diabetes is a condition where the blood glucose levels are not able to be regulated as the insulin-secreting cells in the pancreas are not able to produce insulin
  • This means that blood glucose levels are often far too high
  • It can be treated by injecting insulin
  • The extra insulin causes the liver to convert glucose into glycogen, which reduces the blood glucose level
  • Symptoms of diabetes include extreme thirst, weakness or tiredness, blurred vision, weight loss and loss of consciousness in extreme cases
  • People with Type 1 diabetes have to monitor their blood glucose levels throughout the day as their levels of physical activity and their diet affect the amount of insulin needed
  • They can help to control their blood glucose level by being careful with their diet –  eating foods that will not cause large increases in blood glucose level, and by exercising, which can lower blood glucose levels due to increased respiration in the muscles

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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