Diabetes Glossary Terms: H-K

these are the human leucocyte antigens. There are four genes responsible for their production (A, B, C, D), which are located on chromosome 6, which makes up the HLA system. One gene or set of genes is inherited from each parent and produce the HLA antigens on the surfaces of cells throughout the body. These antigens are the means by which the immune system recognizes 'self and rejects 'non-self, and this is very important in organ transplantation. The closer the match of HLAs between donor and recipient, the greater the chances of success. If two individuals share identical HLA types, they are described as histocompatible.

a chemical substance that is naturally produced by the body and acts as a messenger. A hormone is produced by cells or glands in one part of the body and passes into the bloodstream. When it reaches another specific site, its 'target organ', it causes a reaction there, modifying the structure or function of cells, perhaps by causing the release of another hormone. Hormones are secreted by the endocrine glands, and examples are the sex hormones, e.g. testosterone, secreted by the testes, and oestradiol and progesterone, secreted by the ovaries.

the presence of excess sugar (glucose) in the blood, as in diabetes mellitus, caused by insufficient insulin to cope with carbohydrate intake. The condition can lead to a diabetic coma.

high blood pressure (in the arteries). Essential hypertension maybe the result of an unknown cause or kidney disease or endocrine diseases. Malignant hypertension will prove fatal if not treated. It may be a condition in itself or an end stage of essential hypertension. It tends to occur in a younger age group, and there is high diastolic blood pressure and kidney failure. Arteriosclerosis is a complication of, and often associated with, hypertension. Other complications include cerebral haemorrhage, heart failure and kidney failure. Previously a rapidly fatal condition, antihypertensive drugs have revolutionized treatment and given sufferers a near-normal life.

a lack of sugar in the blood, which occurs in starvation and also with diabetes mellitus when too much insulin has been given and insufficient carbohydrates have been eaten. The symptoms include weakness, sweating, light-headedness and tremors, and can lead to coma. The symptoms are alleviated by taking in glucose, either by mouth or by injection in the case of hypoglycaemic coma.

clusters of cells within the pancreas, which are the endocrine part of the gland. There are three types of cells, termed alpha, beta and delta, the first two producing glucagon and insulin respectively, both vital hormones in the regulation of blood-sugar levels. The third hormone produced is somatostatin (also released by the hypothalamus), which works antagonistically against growth hormone by blocking its release by the pituitary gland. The islets were named after Paul Langerhans, a German pathologist.

the normal production of ketones in the body because of metabolism of fats. Excess production leads to ketosis.

an organic compound that contains a carbonyl group (C = 0) within the compound. Ketones can be detected in the body when fat is metabolized for energy when food intake is insufficient.

one of several compounds (e.g. acetoacetic acid) produced by the liver as a result of metabolism of fat deposits. These compounds normally provide energy, via ketogenesis, for the body's peripheral tissues. In abnormal conditions, when carbohydrate supply is reduced, ketogenesis produces excess ketone bodies in the blood (ketosis) which may then appear in the urine (ketonuria).

the presence of ketone bodies in the urine as a result of starvation or diabetes mellitus, causing excessive ketogenesis and ketosis.

the build-up of ketones in the body and bloodstream because of a lack of carbohydrates for metabolism or failure fully to use the available carbohydrates, resulting in fat breakdown. It is induced by starvation, diabetes mellitus, or any condition in which fats are metabolized quickly and excessively.

a genetic imbalance in males in which there are 47 rather than 46 chromosomes, the extra one being an X-chromosome, producing a genetic make-up of XXY instead of the usual XY. The physical manifestations are small testes that atrophy, resulting in a lack of sperm production, enlargement of the breasts, long thin legs and little or no facial or body hair. There may be associated mental retardation and pulmonary disease.