Defining Diabetes

Diabetes is caused by a complete or partial deficiency of insulin or a lack of its effects. Hence the defect may be in the production and release of the hormone or it may occur at receptor or post-receptor level. The second situation is known as insulin resistance and the problem may lie with the receptors themselves or with post-receptor events. If the receptors themselves are involved, it may be because they are too few in number or because they have lost some of their ability to bind to insulin. Defects in insulin receptors can sometimes be corrected with treatment, but in very rare cases they may be a part of a severe, inherited condition.

Malfunction in post-receptor events preventing insulin from performing its normal metabolic actions is quite common. Usually, there is a degree of impairment, so that the actions of insulin are rendered less effective, rather than a complete breakdown of the system. Post-receptor defects are highly complex, may not be reversible, and are a prominent feature in the most common form of diabetes, type 2 diabetes. The other main reason for insulin deficiency has to do with defects in the pancreatic beta cells of the islets of Langerhans.

Whatever the reason, or combination of reasons, behind the deficiency of insulin, the effect is to cause a sustained rise in the level of blood glucose or hyperglycaemia. An elevated level of blood sugar is the defining feature of diabetes mellitus but this does not always produce a clear-cut set of symptoms. The syndrome ranges from producing no symptoms at all to severe illness due to acute and potentially fatal metabolic complications. In general, severity of symptoms is related to the degree of insulin deficiency, although there are other factors which may influence this. One of the functions of insulin is regulation of the normal salts/water balance.

Hyperglycaemia may result in glucose entering the urine and disruption of the body's normal electrolytes (salts) to water ratios in the tissues. A feature of this imbalance is that the person passes an abnormally large quantity of urine (polyuria), and this may be particularly the case during the night (nocturia). Excessive urination leads to further loss of salts such as sodium and potassium and an increased thirst, so that the person drinks excessively. Increased urination, thirst and excessive drinking in diabetes may be medically referred to as osmotic symptoms. The presence of sugar in the urine quite commonly encourages opportunistic infections by yeast organisms (thrush), with irritation and itching around the external opening of the urethra.

High glucose levels in the blood can affect the lens of the eye which may become swollen, causing inability to focus and a blurring of vision. This is a temporary and reversible situation which is rectified with treatment for the diabetes, as distinct from diabetic retinopathy which is a potential long-term complication of the syndrome. Other symptoms that are quite common in diabetes include recurrent infections such as boils, mood swings and irritability, and a tingling 'pins and needles' sensation in the feet and hands.

If deficiency in insulin continues to be severe, the mechanisms described in the previous section accelerate as fat and protein are broken down in the liver's attempt to provide the body with energy. As a result, blood glucose levels rise even higher, but the continuing lack of insulin means that the body remains deprived of energy. Symptoms of this include extreme tiredness and rapid weight loss. In serious cases, as a result of ketogenesis, ketosis or acidosis occurs and there is a build up of ketones in the blood, from which they pass into the urine (ketonuria). There may be a detectable smell of acetone from the person's breath. In extreme and severe untreated cases, there may be a progression to a serious and potentialy fatal condition called diabetic ketoacidosis (DKA).

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