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Fig. 10.3 The metabolic pattern in untreated Type 1 diabetes. Pathways accelerated by insulin deficiency are marked '+', pathways inhibited (particularly glucose uptake by insulin-sensitive tissues such as muscle, and triacylglycerol removal by lipoprotein lipase), are marked '-'. LPL, lipoprotein lipase; NEFA, non-esterified fatty acids; TAG, triacylglycerol.

Fig. 10.3 The metabolic pattern in untreated Type 1 diabetes. Pathways accelerated by insulin deficiency are marked '+', pathways inhibited (particularly glucose uptake by insulin-sensitive tissues such as muscle, and triacylglycerol removal by lipoprotein lipase), are marked '-'. LPL, lipoprotein lipase; NEFA, non-esterified fatty acids; TAG, triacylglycerol.

in the blood rises dramatically. The normal 'resting' concentration of around 5 mmol/l may increase to 10, 20 or even 50 mmol/l as the disease progresses. In addition, the change in blood glucose concentration when glucose or carbohydrate is ingested becomes exaggerated - the person is said to display poor glucose tolerance. This feature is commonly used for diagnosis of diabetes mellitus (Box 10.2).

The increased glucose concentration of the blood, known as hyperglycae-mia, leads to loss of glucose in the urine. At normal blood glucose concentrations, glucose is not lost by the kidney; it is filtered at the glomerulus and reabsorbed in the proximal tubules. But when the blood concentration rises above about 12 mmol/l, the level known as the renal threshold, reabsorption becomes saturated and glucose 'spills over' into the urine. This would lead to a hyperosmolar urine, so more water is lost through the process known as osmotic diuresis. Hence we see the classic sign of increased production of sugary urine. Loss of this extra water leads, of course, to thirst, the other classic sign of diabetes mellitus. People who develop Type 1 diabetes are usually first driven to their doctor by a combination of weight loss, thirst and frequent urination; treatment with insulin rapidly reverses these changes and restores their feeling of health.

The changes in glucose metabolism are usually regarded as the 'hallmark' of diabetes mellitus, and treatment is always monitored by the level of glucose in the blood. However, it has been said that if it were as easy to measure fatty

Box 10.2 Diagnosis of diabetes mellitus

Diabetes mellitus is defined as an elevation of the plasma (or blood) glucose concentration. It may be diagnosed by a measurement of the plasma glucose concentration after an overnight fast, but usually the disease is more clearly unmasked by observing the response of the plasma glucose concentration after drinking a solution of 75 g glucose, the oral glucose tolerance test. The World Health Organization has specified limits for definition of diabetes and of less severe changes known as impaired fasting glucose and impaired glucose tolerance: the last two categories are not recognised as diseases themselves but they show people at risk of developing diabetes.

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Delicious Diabetic Recipes

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