Glucose Hypoglycaemia

Hypoglycaemia A lower-than-normal blood glucose concentration. 

Hypoglycaemia remains the most frequent complication of insulin administration to diabetics. It usually occurs due to (a) administration of an excessive amount of insulin (b) administration of insulin prior to a mealtime, but with subsequent omission of the meal or (c) due to increased physical activity. In severe cases this can lead to loss of consciousness, and even death. Although it may be treated by oral or i.v. administration of glucose, insulin-induced hypoglycaemia is sometimes treated by administration of glucagon. 

An excess of insulin can cause hypoglycaemia and the hormones that respond to this condition to restore normal glucose levels are known as the counter-regulatory hormones. They are adrenaline, glucagon, growth hormone and cortisol. An increase in the blood levels of these hormones can sometimes be used to conhrm a diagnosis of hypoglycaemia. 

The concentration of glucose in the blood is maintained as a balance between rates of glucose utilisation and glucose supply and changes in one or both of these can lead to hypoglycaemia. Three situations are considered. 

Hypoglycaemia caused by stimulation of the rate of glucose utilisation and inhibition of the rate of release of glucose by the liver... 

This situation arises mainly when the blood level of insulin is high - abnormally high for the given condition. Insulin not only stimulates peripheral utilisation but also inhibits glucose output by the liver so that hypoglycaemia can develop rapidly. Four examples are given. 

Hypoglycaemia that arises when an increased rate of utilisation exceeds that of glucose release by the liver... 

The specific gluconeogenic enzymes in the liver of the foetus develop late in pregnancy, so that premature babies can develop hypoglycaemia soon after birth and provision of glucose is essential for their survival. 

Ketone bodies are oxidised by most aerobic tissues including skeletal muscle, heart, kidney, lung, intestine and brain. Since the last two cannot oxidise fatty acids, their ability to oxidise ketone bodies is very important, because they provide another fuel in addition to, or as an alternative to, glucose. Hence, they can be used to replace some of the glucose to maintain the blood glucose concentration (e.g. in prolonged starvation or hypoglycaemia). 

The plasma ketone body level increases rapidly in starvation in pregnancy, which is important in preventing hypoglycaemia in the mother and thus maintaining a supply of glucose for the developing foetus (Chapter 19). 

Glucose is an essential fuel for the brain and, if the blood concentration falls, uptake by the brain decreases and less fuel is available for ATP generation in the neurones. This results in a decrease in the ATP/ADP concentration ratio. Consequently, less energy is released on ATP hydrolysis, so that less is available for synthesis, transport of neurotransmitter within the nerve and release into the synapse. Hypoglycaemia could, therefore, reduce the effectiveness of neurotransmitters which would reduce stimulation of the motor control pathway. The result would be inhibition of muscle contraction (Figure 13.27). 

In the fed state, the only fuel used by the brain is glucose, derived from the blood. In prolonged starvation or chronic hypoglycaemia, ketone bodies are nsed which rednce the rate of utilisation of glucose by the brain bnt, even so, glucose still provides about 50% of the energy. Consequently, under all conditions, maintenance of the blood glucose concentration is essential for the function of the brain the mechanisms that are responsible for this are discnssed in Chapters 6, 12 and 16. 

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