Glucose metabolism and diabetes mellitus
Dietary carbohydrate is digested in the gastrointestinal tract to simple monosaccharides, which are then absorbed. Starch provides glucose directly, while fructose (from dietary sucrose) and galactose (from dietary lactose) are absorbed and also converted into glucose in the liver. Glucose is the common carbohydrate currency of the body. Figure 31.1 shows the different metabolic processes that affect the blood glucose concentration. This level is, as always, the result of a balance between input and output, synthesis and catabolism.
Insulin
Insulin signals the fed state. It switches on pathways and processes involved in the cellular uptake and storage of metabolic fuels, and switches off pathways involved in fuel breakdown (Fig 31.2). It should be noted that glucose cannot enter the cells of most body tissues in the absence of insulin.
Diabetes mellitus
Primary diabetes mellitus is generally subclassified into Type 1 or Type 2. These clinical entities differ in epidemiology, clinical features and pathophysiology. The contrasting features of Types 1 and 2 diabetes mellitus are shown in Table 31.1.
Table 31.1
Type 1 versus Type 2 diabetes mellitus
| Main features | Type 1 | Type 2 |
| Epidemiology | ||
| Frequency in northern Europe | 0.02–0.4% | 1–3% |
| Predominance | N. European | Worldwide |
| Caucasians | Lowest in rural areas of developing countries |
