Energy is constantly required in human life, whereas it is supplied only by intermittent food intake. Therefore, food is usually ingested in excess of the immediate caloric needs, and the extra calories are stored in the form of hepatic and muscle glycogen, adipose tissue triglycerides, and to a certain extent as muscle protein. In turn, these fuel reservoirs are broken down during starvation to provide energy for the body. The amount of glycogen stored in skeletal muscle is about 400 g (1600 Kcal), the amount of glycogen in liver is about 75 g (300 Kcal), and the amount of triglycerides stored in adipose tissue is about 15 000 g (141 000 Kcal), at overnight fasting state in healthy men.
Glucose and free fatty acids, which are stored as glycogen and triglycerides, respectively, are the two principal circulating fuels in humans. Endogenous glucose is produced by gluconeogen-esis in the liver and glycogenolysis not in skeletal muscle but in the liver .
Energy reservoirs in humans are built up and broken down in response to hormonal messages. Insulin is the principal hormonal messenger and has an anabolic effect. It is a major regulator of glycogen storage and its most important action is to enhance glycogen synthesis [2,3]. In the metabolism of fat, insulin inhibits lipolysis and induces the storage of triglycerides in adipose tissue .
Diabetes mellitus is a syndrome characterised by chronic hyperglycaemia and disturbances of carbohydrate, fat, and protein metabolism associated with absolute or relative deficiencies in insulin secretion and/or insulin action. Diabetes mellitus has been classified into four groups: type 1, type 2, other specific types, and gestational diabetes. Type 1 diabetes results from destruction of the beta-cells of the pancreas, usually leading to absolute insulin deficiency. There are two forms of type 1 diabetes, immune-mediated diabetes and idiopathic diabetes. Type 2 diabetes refers to individuals who have insulin resistance and, usually, relative insulin deficiency. There are probably many different causes of type 2 diabetes. Other specific types of diabetes include those induced by genetic defects of beta-cell function, genetic defects in insulin action, diseases of the exocrine pancreas, endocrinopathies, drug- or chemical-induced diabetes, infections, uncommon forms of immune-mediated diabetes, and other genetic syndromes .
Whereas the metabolic disorders in type 1 diabetes may be explained by a lack of insulin, the basis for the metabolic abnormalities in type 2 diabetes is unclear but may be the end result of several defects in insulin action. Type 2 diabetes appears to develop in patients with acquired (diet- or obesity-related) and genetically programmed insulin resistance, when the pancreatic beta-cells are no longer able to produce extra insulin to counteract the effects of resistance .
Weight loss is one of the major symptoms of diabetes with marked hyperglycaemia, in addition to polyuria, polydipsia, sometimes polyphagia, and blurred vision.
As beta-cell dysfunction progresses, plasma glucose levels increase even in the fasted state because of increased hepatic glucose production. With more severe insulin deficiency, plasma free fatty acid levels increase as a consequence of enhanced lipolysis. The most extreme form of poorly controlled diabetes mellitus is diabetic ketoacidosis. The combined effects of the insulin deficiency and the increase in the levels of counter-insulin hormones result in an increase in the break down of glycogen, triglycerides, and protein beyond the fuel needs of the patient. Furthermore, the ability of peripheral tissues to utilise glucose and ketone bodies is impaired. Therefore, large quantities of these fuels are lost in the urine, resulting in weight loss in diabetic patients.
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Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...