Blood glucose regulation

• Glucose is an essential substrate for energy supply
• Is broken down in aerobic and anaerobic respiration to release energy for ATP production
• Is because high blood glucose levels cause complications such as increased blood pressure, cardiovascular disease, nerve damage, blindness and increased infections 
• Body therefore has homeostatic processes, including negative feedback, that operate to keep glucose levels within the tolerance range
• Chemoreceptors in the Islets of Langerhans in the pancreas detects changes in blood glucose levels in the blood
• In response to an elevated blood glucose level (e.g. after eating carbohydrates), insulin (peptide hormone) is released from the beta (b) cells of the Islet of Langerhans into the blood
• Insulin binds to specific receptors on cells, especially liver, muscle and adipose (fat) cells, stimulating them to take up glucose from the blood
• Under normal circumstances (non diabetic), the blood glucose levels will decrease to normal tolerance range as a result
• This is detected by the chemoreceptors, resulting in the termination of insulin release
• This is an example of negative feedback, where the response reverses the stimulus
• Glucose can be used for respiration by these cells or stored
• The liver is the major store of carbohydrates, and converts excess glucose absorbed from the blood into a complex carbohydrate called glycogen
• In response to decreased blood glucose levels (e.g. when exercising or fasting), glucagon (peptide hormone) is released from the alpha (A) cells of the Islets of Langerhans into the blood
• Glucagon binds to specific receptors on liver cells, which stimulates them to break down their glycogen stores into glucose and release the glucose into the blood
• This increased blood glucose levels back into the normal tolerated range
• This is detected by the chemoreceptors, resulting in the termination of glucagon release
• This is also an example of negative feedback