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Insulin Deficiency

The diabetic, who is short of insulin, cannot easily produce n this chemical cycle of metabolism a straightforward transfer of blood glucose across to the cell. The effect of insulin is also needed in the liver to mobilize the change of glucose to ketones and fat so that, when insulin in insufficient to a person's needs, there is a shortage of energy for the body's cells, a breakdown of the body's fats, a loss of weight and the state of ketosis occurs where the blood is loaded with unusable sugar, ketones and fatty acids.

Insulin, therefore, has its single most important function in the use of carbohydrate as energy, and it also aids the body's use of fatty acids that may be taken in as foodstuffs. Since the body, in an emergency, can break down its own protein to give energy and so lose its muscle bulk as well, a defect in the insulin role will inevitably affect the whole of the body's metabolism.

As everyone recognizes, fat is a long-term storage material, put away for use in times of deprivation. When glucose reaches the liver, therefore, it is altered again by the use of special enzymes to what are known as fatty acids, chemically called triglycerides. These re-circulate in the blood as fat in the abdomen, below the skin, in the breasts, thighs and buttocks. Thus anyone who overeats, or takes in more carbohydrate in their diet than their body cells need, gets fat. Similarly, if the body is deprived of energy from carbohydrate, or needs more that it can get in the diet, the body fat is broken down and the cycle of glucose metabolism is reversed. The fat becomes a fatty acid (this time a ketone), the liver converts the ketone back to glucose and the cell then absorbs the glucose. Therefore, in starvation or illness, the body loses its fat stores, and its weight and becomes thin.

In the healthy person there is normally no defect in the supply of insulin available from the pancreas. After eating a meal, the fasting blood sugar rises to 150 mg/ 100 ml of blood within 30 to 60 minutes. A rising blood sugar signals the pancreas that more insulin is needed, and the islet cells secrete more in response to the rise to bring the blood-sugar level down again. Once it has leveled off, the islet cells 'rest' and the insulin secretion drops. If the blood level of sugar rises above 170 mg/ 100 ml, the kidney cells cannot cope with their normal re-absorption of this special energy-giving substance and so they have to let it 'slip through' into the urine. This spillover causes sugar to appear in the urine technically termed glycosuria and in most people this is the earliest detectable sign of diabetes occurring. Some individuals, however, have a lower threshold to the excretion of sugar, and glycosuria can develop simply after a rich and sweet-laden meal. In those cases it is not diabetes that is responsible, because their insulin secretion rate is normal; it is just that' their kidney cells are less efficient than most. Sometimes, in pregnancy, sugar is discovered in the woman's urine, as a apart of the routine tests done at each antenatal visit, but again this may be due to a reduced efficiency of the kidney a spillover effect once more, and not to be taken as a sign of diabetes.

In the diabetic, as we have already noted, the insulin deficiency means that the blood sugar continues to rise, the cells are deprived of their life-sustaining fuel, the body breaks down its fats and the sugar is wasted in the urine. Surprisingly, however, the diabetic may not be simply producing less insulin than the healthy person is; they may in fact be producing more than is normal, but even then not enough for their own particular needs. Evidence has shown that, if the blood-insulin levels of individuals who are going to become insulin-dependent (i.e., those developing the early symptoms of diabetes) are compared with those of normal people, the diabetics do have higher level. What happens to this excess, therefore, when clearly, despite the increased output of insulin, they do not have enough, or they would not be diabetic? The suggestion is that diabetics may have something in their bloodstream that is an antagonist to insulin, or a neutralizer. If they have, then the explanation as to why they produce more and perhaps ultimately fail to keep up with a rising need and so literally exhaust their pancreas and then become frankly diabetic is logical. So far, however, attempts to accurately define what the insulin neutralizer is have not been completely successful.

What is clear is that a person with the signs of diabetes needs extra insulin, or else special dietary control to prevent the overload of their metabolism that sparked it all off. The alternative of special drugs that can be taken by mouth which both lower the blood sugar and, it would seem, stimulate an aging or failing pancreas to greater effort is one for the older person (see 'Treatment'). Insulin, unfortunately, cannot be given as a tablet or medicine by mouth. It is in fact a protein substance, biochemically, and is therefore broken down and its effects neutralized by the stomach's digestive juices, and thus must be given by injection.

There are many different types of insulin, (see 'Treatment') tailored to give a different duration of effect, from the short-acting to the long-acting, and they are all derived from animal sources. Insulin is produced today, as it first was by Banting and Best 60 years ago, from an extract of animal pancreas (either from beef or pork). The pancreas of an animal is known to the butcher as the 'sweetbread', an interesting name in view of its biological function in the live animal, and it is somewhat rare in its appearance on menus since the majority of the world's supply is purchased by drug manufacturers to make insulin. Recent research has shown, however, through genetic 'engineering' of bacteria, the possibility of 'teaching' cultures of bacteria to make insulin, and it may be that, in future, this, will form the world's main source of the purified protein. At present, though, it is chemically impossible to make it artificially, and every diabetic who requires it has to inject it daily according to their needs.

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