Glucose metabolism and diabetes mellitus

31


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 is the principal hormone affecting blood glucose levels, and an understanding of its actions is an important prerequisite to the study of diabetes mellitus. Insulin is a small protein synthesized in the beta cells of the islets of Langerhans of the pancreas. It acts through membrane receptors and its main target tissues are liver, muscle and adipose tissue.


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.



The effects of insulin are opposed by other hormones, e.g. glucagon, adrenaline, glucocorticoids and growth hormone. These are sometimes called stress hormones, and this explains why patients admitted acutely to hospital often have raised blood glucose.



Diabetes mellitus


Diabetes mellitus is the commonest endocrine disorder encountered in clinical practice. It may be defined as a syndrome characterized by hyperglycaemia due to an insulin resistance and an absolute or relative lack of insulin.


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























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Jun 18, 2016 | Posted by in BIOCHEMISTRY | Comments Off on Glucose metabolism and diabetes mellitus

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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