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Diabetes Mellitus: Its Clinical Significance, Classification And The Medical Relevance Of The Insulin
A Diabetic Mother
Diabetes mellitus is a metabolic disorder where there is hyperglycemia and glucosuria due to a deficiency of effective insulin in the body. Diabetes mellitus is one of the most widespread affections of mankind. There is sufficient evidence to conclude that the incidence of diabetes mellitus is increasing. In developing countries, about 3% of the Urban population and 1.5% of rural population suffer from the disease. The incidence increases with age. Male to female ration is about 2:1. In Western countries, diabetes is more common in females. It is mainly characterized by an absolute or relative deficiency of effective insulin. This may be brought about by impairment of insulin production of release by the beta cells of the islets of Langerhans in times of need or an imbalance between insulin and its antagonists, the latter predominating. This is associated with microangiopathy which is a specific vascular involvement seen in diabetes mellitus. There is also a tendency for accelerated macro-angiopathy.
Classification: Diabetes may be primary or secondary. Primary diabetes is classified into insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). The main criterion is clinical, based on the requirement of insulin to control the hyperglycemia. Though in the vast majority of cases, this classification is satisfactory, in a fee cases, a strict differentiation cannot be made. The IDDM is generally seen in juveniles (10- 12 years) and young, and they are prone to develop ketosis. The NIDDM is usually the maturity- onset type (50 to 70 years) and ketosis is less common in them. Numerically, NIDDM accounts for more than 90% of the total cases. In addition, diabetic syndromes may develop secondary to several under-mentioned disorders.
- Pancreatic causes: Chronic pancreatitis, carcinoma pancreas, hemochromatosis, pancreatectomy.
- Endocrine disorders: Cushing’s syndrome, acromegaly, pheochromocytoma, hyperthyroidism, glucagonoma.
- Drug-induced diabetes mellitus: Corticosteroids, ACTH, thiazide diuretics, diazoxide, oral contraceptives.
- Insuline receptor abnormalities lead to the diabetic state.
Genetic syndromes presenting with diabetes
- An Autosomal recessive disorder comprising of diabetes insipidus, diabetes mellitus, optic atrophy and deafness.
- Synthesis of pro-insuline and insulin may be defective due to genetic defects.
- Lipoatrophic diabetes is characterized by the complete absence of fat from all tissues.
An Insulin Pump
This is the hormone produced by the beta cells of the islets of Langerhans and is composed of two polypeptide chains A and B linked together by two disulphide bones. The precursor of insulin is proinsulin (big insulin) from which C-peptide is broken off to form insulin. Insulin is stored in the granules of the beta cells to be discharged into the interstitial fluid, under appropriate stimulus. Though proinsulin crossreacts with insulin antibodies, it has none of the metabolic effects of insulin.
Main stimulus for formation and release of insulin is hyperglycemia caused by ingestion of carbohydrates. Other stimuli include hyperaminoacidemia caused by protein ingestion and the peptide hormones like glucagon, gastrin, pancreozymin and secretin. Insulin reaches its target cells through blood. Levels of circulating insulin vary during the different periods of the day. It is lowerst in the fasting state (10- 30 uml). On the target cell, insulin binds to specific surface receptors and then initiated further biochemical events within the cell. Alteration of the cell membrane by insulin favours the entry of glucose, potassium and aminoacids into muscles, liver and fat cells. In the liver, insulin retards gluconeogenesis. Excess glucose entering the skeletal muscles is converted into glycogen. Insulin helps to build up adipose tissue by aiding the conversion of glucose into fatty acids from fat cells. In conjunction with growth hormone, insulin enhances the incorporation of amino acids into peptides in the liver and skeletal tissues.
Different mechanisms may lead to the development of diabetes mellitus. These are: (1) lack of synthesis of insulin, (2) defect in the release of insulin, (3) defect in the transport mechanism in blood, and (4) deficiency in the number and/or affinity of the receptors. The final outcome is hyperglycemia with glycosuria and osmotic dieresis and their consequences.
© 2014 Funom Theophilus Makama