Sunday 20th August 2017

Diabetes

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Diabetes Mellitus

There are two different diseases called diabetes, which are unrelated although they share some symptoms, such as excessive thirst and urination. One is Diabetes Insipidus, a rare condition in which the patient frequently excretes huge quantities of diluted urine, and as a consequence has a great thirst and consumes enormous amounts of liquids. Diabetes Insipidus is in most cases caused by a deficiency of the antidiuretic hormone, secreted in the hypothalamus, stored and released from the pituitary gland in the brain, and regulating the balance of fluid in the body and the quantity of urine produced by the kidneys.

The other is the much more common Diabetes Mellitus (mellitus derives from the Latin miele, honey), also called "sugar diabetes" or ordinary diabetes, which is the subject of this article.

To understand the complex disease which is Diabetes Mellitus, let's start from the beginning, from the pancreas. The pancreas is an organ of both the digestive and endocrine systems, a large gland which has two main functions: it manufactures important digestive juices, and also in some specialised areas, called the Islets (or Islands) of Langerhans from their discoverer, it has the beta-cells that produce insulin, a peptide (protein-like) substance made up of 51 amino acids and the hormone which enables the body to utilize sugar. A relatively common flaw in the genetic message causes the defective conversion of a precursor of insulin, proinsulin, to insulin itself, leading to elevated proinsulin to insulin ratio. This failure to produce insulin is one of the main causes of Diabetes Mellitus.

Diabetes is a disorder of sugar metabolism, so we need to have to look at this. What happens after we have eaten? Our digestive system breaks down the stomach contents, food, into glucose, a simple sugar. This takes place over several hours after a meal. But the body needs energy even after digestion is terminated. So it stores reserves that can be drawn upon later.

Glucose, or blood sugar, the energy substance par excellence in the metabolism of the cell, after being absorbed by the intestines, is mostly accumulated, for the body's needs, in the liver cells. It is stored there as glycogen, a compact substance whose giant molecule with a highly branched structure is composed of chains of glucose molecules, that is, it is a glucose polymer.

Around 10 percent of our liver mass and 1 per cent of our muscles are made up of glycogen. The cells in our liver and muscles manufacture glycogen from some of the sugar they receive after digestion, and stocks it up as small granules around 1-4 thousandths of a millimetre across: they are the pantries of the cell.

Sugar levels in the blood below a certain level trigger the pancreas' production of two hormones, epinephrine and glucagon, which instruct cells to start using their glycogen reserves by breaking apart glycogen into glucose. Excessive sugar in the blood triggers the opposite warning system, i.e the pancreas' production of insulin, which tells cells to start converting glucose to glycogen, that is, to store glucose instead of burning it. Insulin also instructs cells to start manufacturing, making for instance proteins and fats, another emergency fuel reserve, instead of generating energy.

In normal conditions the insulin manufactured in the pancreas drives the glucose through the bloodstream to the body's various cells. Cells of insulin-responsive tissues, such as muscle cells, fat cells and others, have insulin receptors. When insulin attaches to a receptor, it activates chemical reactions that allow glucose to enter the cell.

In Diabetes Mellitus, the most serious disorder of carbohydrate metabolism, the beta-cells in the Islands of Langerhans of the pancreas are damaged or present in insufficient number, which means that insulin is absent or insufficient.

So in diabetic patients blood cannot deliver glucose to cells because, without insulin, the membranes of certain cell types that need insulin to absorb glucose, including muscle and adipose cells, will reject the sugar.

The unused glucose accumulates in the blood and acts as a poison. Diabetes is a very serious chronic disease, which, in extreme cases, is a leading cause of heart problems, kidney failure, amputation, blindness, coma and even, although not so frequently now as in former times, premature death.

 

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Diabetes Type 1 and 2

There are two main types od diabetes: type 1 diabetes and type 2 diabetes.

Type 1 diabetes, or insulin-dependent diabetes mellitus or IDDM, is sometimes called juvenile diabetes because it is most frequent in people under 40 years. It is caused by a lack of beta-cells, the insulin-secreting cells in the Islets of Langerhans in the pancreas. Type 1 diabetes is usually an autoimmune disorder in which the immune system attacks and kills the body's own insulin-producing cells. Why this happens is still not entirely clear: epidemiological evidence suggests a genetic predisposition, and recent autopsy research supports the hypothesis that viral infections, in particular from enteroviruses, may trigger diabetes type 1 in genetically susceptible individuals, while some researchers also believe cow's milk to have the same effect.

The vast majority, three quarters, of diabetics have type 2 diabetes, or noninsulin-dependent diabetes mellitus or NIDDM, also called adult-onset diabetes. It develops more slowly than type 1 and with less severe symptoms in the initial stages. In these patients the pancreas produces insulin, but it is either insufficient for the body's needs or is not effectively used. The groups most at risk of developing diabetes type 2 are people over 40 who are overweight, have a diabetic close relative, are Afro-Caribbean or Asian, or have been diabetic while pregnant.

When diabetes develops early in life, then, it is because the pancreas does not produce enough insulin. Adult-onset diabetes is dissimilar: there is a sufficient supply of insulin, but the cells do not respond to it adequately. Generally, diabetes is more severe in young people than in older patients. There are different types of diabetes, but in all types insulin receptors do not work as they should, even when there is adequate glucose. The latter, as a consequence, accumulates in the bloodstream, increasing blood sugar to dangerously high levels.

To simplify, the causes of diabetes are: a) insulin resistance at the cell level, b) lack of insulin production by the pancreas.

Insulin resistance (IR) is a physiological condition in which the body's cells become resistant to the effects of insulin and the normal reaction to a certain amount of insulin is lower. As a consequence, greater quantities of insulin are necessary for insulin to be effective.

Providing cells with sugar is in normal conditions possible only in the presence of insulin, which accelerates the transfer of sugar from blood to cell. If, in the case of diabetes, insulin is deficient, sugar could reach the inside of the cells only if its concentration in the blood increased, taking advantage of the simple physics laws of diffusion. In this case, however, to provide the cell with sufficient sugar, we would need blood sugar concentrations 5 times greater than those effective in the presence of insulin. A high concentration of sugar in the blood of diabetics is both a symptom of the illness and a way to provide cells with sugar even in the absence of insulin.

 

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