Gangrene - the death of tissue on a large scale. May be caused by certain bacteria which spread rapidly through tissues, or by an inadequate1 blood supply.

Ganglion - a collection of nerve cells usually found outside the central nervous system, from which axons arrive from the periphery and proceed to the spinal cord or brain.

Gene cloning - a technique which uses recombinant DNA, inserted into a host cell as a plasmid which reproduces copies of itself, and hence the inserted gene, many times

Generic - belonging to the same main group. For example generic medicines are identified by the main group they fall into rather than by their trade names.

Genes - the unit of inheritance that transmits information from one cell to its daughters and hence to the next generation. A gene consists of a specific series of DNA nucleotides. Each three nucleotides is the code for an amino acid. Humans have about 200,000 genes which collectively are know as the genome.

Genetic engineering - see recombinant DNA.

Genome - the complete complement ofgenetic material in a species.

Gingival crevice fluid - a secretion found in the gingival sulcus, formed by the cells attaching the gingival epithelium to the tooth.

Gingival sulcus - a potential space between the gingival margin12 and the tooth, lined by non-keratinised epithelium. The depth of the sulcus is normally between 1 and 2 mm in health.

Gingivitis - an inflammation of the gingival mucosa, due to the increase in the virulence13 or mass of bacteria in the gingival sulcus, or to reduced resistance of the host.

Glands - a collection of cells secreting a specific product such as insulin or sweat.

Glucocorticoids - one of the two major hormones secreted by the adrenal medulla. The most common glucocorticoid is cortisol (hydrocortisone) but they all share the common effect of increasing blood glucose18 concentration. They may achieve this at the cost of body protein stores, by converting amino acids into glucose. Cortisol also converts fatty acids into glucose. Any type of stress, including trauma, infection, fear, anxiety or malnutrition20 causes an increase in cortisol secretion. Cortisol stabilises the membrane21 of lysosomes, which are then unlikely to rupture, a process which stimulates inflammation. Cortisol therfore inhibits inflammation. Cells like neutrophils, are less able to protect the body from foreign proteins. Stress therefore reduces the bodies ability to cope with infection. Malnutrition not only stunts mental and physical development but also allows viral, bacterial and parasitic infections to flourish.

Glucosamine - a glucose or galactose molecule with an amine group attached. see also glucuronic acid.