Gangrene - the death of tissue on a large scale. May be caused by certain bacteria which spread rapidly through tissues, or by an inadequate 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 margin 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 virulence 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 glucose 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 malnutrition causes an increase in cortisol secretion. Cortisol stabilises the membrane 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.

    Glucose - a molecule of great importance to life as it provides a ready source of energy for both plant and animal cells. Glucose can only be formed in plants with the aid of sunlight. This process of photosynthesis sustains all animal life on earth. The glucose molecule is formed by a ring of a six carbon atoms. It is progressively broken down in a process called glycolysis during both aerobic and anaerobic respiration into ATP

    Glucuronic acid- a glucose molecule with an acid carboxyl group. One of the two molecules which makes up the repeating disaccharide unit of glycosaminoglycans other molecule is a glucosamine.

    Glycine - one of 20 amino acids commonly found in proteins.

    Glycogen - a polysaccharide made up of repeated glucose units. Animals make glycogen and store it in liver and muscles.

    Glycolysis - the breakdown of glucose in series of metabolic steps. Energy in the form of ATP is released even if there is no oxygen available as in anaerobic respiration. In the presence of oxygen as in aerobic respiration the breakdown is more complete and yields more energy.

    Glycoproteins - are proteins which have many sugar molecules attached to them. They are an important component of saliva where they provide lubrication for the teeth. They also have a wide range of other functions in connective tissues. Examples are fibronectin, osteonectin, osteopontin and interferon. Glycoproteins are also found in cell membranes where they define part of the cells identity. The four major blood groups are defined by glycoproteins on the cell membranes of red blood cells.

    Glycosaminoglycans (GAGs) - large to huge molecules of the connective tissue matrix, made up of repeating disaccharide units linked to a protein core. The disaccharide units are made of glucosamine and glucuronic acid. The position of a sulphate molecule on the glucosamine determines the type of GAG.

    Golgi apparatus - a cell organelle which is part of the inner cell membrane. It collects and stores the products from the endoplasmic reticulum. It is prominent in actively secreting cells.

    Gomphosis - a form of tooth attachment in which the root is help in a bony socket by a fibrous ligament.

    Gonial angle - the angle made by the posterior part of the ramus and the lower border of the mandible.

    Ground substance - a jelly-like substance which surrounds cells and provides, with fibre, a supportive matrix around each cell. It consists of water and huge molecules which helps transport nutrients to cells and carries away cell products.