Control of Blood Glucose
Explain the control of blood glucose
Normal blood glucose in the non-diabetic is 4-6 mmol.L-1, though will rise after consumption of carbohydrate. Glucose regulation can be divided into:
Regulation via secretion or inhibition of insulin and glucagon from the pancreatic islets.
Regulation via both neuronal (SNS activation) and hormonal (cortisol, GH) mechanisms.
Glucose levels are sensed directly in the pancreas and will result in insulin release when the BGL is >5.6 mmol.L-1. Pancreatic B cells respond directly to glucose by secreting insulin in a biphasic fashion:
- An initial, rapid increase in release
- A prolonged, slow increase in release
- Glutamate is produced as a by-product of the citric acid cycle
- Glutamate stimulates maturation of other insulin granules
- Release of these granules causes the second phase of insulin release
Conversely, a low glucose level stimulates secretion of glucagon. This is typically less important than the effect of insulin unless in situations of starvation or severe physiological stress.
Sustained hypoglycaemia increases fat utilisation and decreases glucose utilisation (limiting further drops in blood glucose), via stimulating release of:
Hypoglycaemia directly stimulates the hypothalamus, causing:
- Increased SNS tone
Adrenaline release in turn stimulates hepatic glucose release.
Glucose levels are influenced by the:
Insulin and glucagon act on the liver to continually adjust the relative rates of glycogenolysis and glycogenesis, allowing it to function as an effective buffer of blood glucose.
- Hepatic disease significantly limits the efficacy of this system, and results in a widely-fluctuating blood glucose level
- A transient glycosuria may be seen as hyperglycaemia decreases renal absorption of glucose
Physiological Responses to Hypoglycaemia
|BSL (mmol.L-1)||Symptoms||Endocrine Response|
|4.6||Insulin secretion inhibited|
|3.8||Autonomic dysfunction||Glucagon, adrenaline, and GH secretion|
|0.6||Permanent brain damage, Death|
- Barrett KE, Barman SM, Boitano S, Brooks HL. Ganong's Review of Medical Physiology. 24th Ed. McGraw Hill. 2012.
- Hall, JE, and Guyton AC. Guyton and Hall Textbook of Medical Physiology. 11th Edition. Philadelphia, PA: Saunders Elsevier. 2011.