Diabetes mellitus is a condition that is commonly known as just "diabetes". However there is another diabetes called diabetes insipidus, which is completely different medically.

Both diabetes mellitus and diabetes insipidus are characterised by passing excessive amounts of urine. In the days before the causes of diseases were known, the two conditions were only distinguished by the fact that the diabetes mellitus produced sweet tasting sugary urine whereas diabetes insipidus produced profuse amounts of urine tasting of water.

Diabetes mellitus is typified by a very high blood sugar, meaning that the glucose is filtered by the kidney into the urine producing the sweet taste and smell. As the urine with high glucose concentration goes through the kidney tubules, the sugar pulls more water out of the blood and into the urine by a process called osmosis, causing excessive urine to be produced and passed.

Diabetes insipidus is caused by the lack of a hormone called ADH (antidiuretic hormone). ADH is released by the posterior pituitary gland, a small gland on the base of the brain. It is actually produced by the hypothalamus and is passed down into the posterior pituitary to be released in into the bloodstream where it circulates to the kidney and has its effect. When ADH is secreted, it allows water to be reabsorbed from the urine back into the blood - reducing the volume of urine produced. This is what happens during the night to stop you needing to go to the toilet when you are asleep.

However, in diabetes insipidus, something has happened to, either the posterior pituitary, the hypothalamus or the connection between the two. ADH is not secreted any more and so urine is passed and no water is reabsorbed. This can result in up to 15 L of urine being produced a day - which left untreated would result in dehydration and death. Fortunately there are synthetic drugs that can be used to replace the ADH.

Diabetes mellitus:

There are two main types of diabetes mellitus known as type 1 or type 2.

Type 1 diabetes mellitus:

In type 1 diabetes mellitus, there is a lack or complete absence of insulin. Insulin is produced by the beta cells of the islets of Langerhans which are found within the pancreas gland. In normal life, the higher the glucose levels in the blood, the more insulin is produced, which pushes the glucose into the cells along with potassium.

The cause of type 1 diabetes mellitus is unknown but it still is usually occur in young life. There seems to be a genetic propensity but also some research suggests that a viral infection early in childhood may predispose to diabetes mellitus.

Type 2 diabetes mellitus:

In type 2 diabetes mellitus, there is usually a decrease in insulin levels although there may be an additional reduction in the action of the available insulin - known as insulin resistance. Type 2 diabetes mellitus tends to come on in later age, and is associated with obesity and alcoholism. The effect of obesity is probably that the requirements for incident over many years means that the body's ability to produce it runs out. Alcohol probably causes type 2 diabetes mellitus by causing pancreatitis, which starts at destroying the beta cells in the islets of Langerhans thus reducing the amount of insulin that can be produced.

Treatment of diabetes mellitus:

• Type 1 diabetes mellitus:

 Type 1 diabetes mellitus needs to be treated by injections of insulin.

• Type 2 diabetes mellitus:

In type 2 diabetes mellitus, the initial treatment is to be careful with diet, both with losing weight and also keeping away from high sugar foods. As the condition worsens, drugs such as metformin might be needed that increase the release of the available insulin as well as enhance its effect. If it continues to deteriorate, in the later stages insulin injections might be required.

Complications of diabetes mellitus:

There are acute complications of diabetes mellitus such as too much sugar causing coma by a condition called a diabetic ketoacidosis, or too little sugar by a condition called diabetic hypoglycaemia. In addition, the extra sugar in the blood stream allows infections but also reduces immunity against them, increasing the risks of absences, septicaemia, urinary tract infections and other infections.

There are also chronic complications of diabetes mellitus. If someone has diabetes mellitus for a long time, it affects their blood vessels. Large blood vessels get hardened and narrow and may block. This can cause heart attacks, gangrene of toes and feet as well as ulcers. Small blood vessels actually increase in number. In the eye, these extra blood vessels cover the retina causing blindness - called diabetic retinopathy.

Importance of treatment:

There is good evidence that diabetic patients who keep very good control of their blood sugar have better long-term quality of life and fewer complications.