Glossary

antibiotic. A substance produced by bacteria or fungi that destroys or prevents the growth of other bacteria and fungi.

antibody. A protein produced by the body's immune system in response to a foreign substance (antigen). An antibody reacts specifically with the antigen that induced its formation and inactivates the antigen. Our bodies fight off an infection by producing antibodies.

bacterium (plural bacteria). A single-celled, microscopic organism without a distinct nucleus.

biopsy. A minor operation that removes cells or tissue for microscopic analysis.

cancer. One of the defining features of most cancer cells is that they grow when they should not. Ignoring signals from the rest of the body, they tend to multiply regardless, encouraging blood vessels to supply them with food and oxygen at the expense of normal tissue nearby. Once a mass of cancer cells (a tumour) has grown large enough, it will often invade other tissues. It will eventually push through the wall of a lymph vessel or blood vessel and clumps of cancer cells will break off and travel around the body. The cancer can then be very hard to cure. The clumps (called metastases) can settle almost anywhere and start to grow as a tumour. The whole body is soon seeded with tumours of the original cancer cell type. Usually, it is then only a matter of time before vital functions of the body are interfered with and the patient dies.

chronic inflammation. Used to describe a medical condition that continues for a long time, often with little change. A chronic disease, such as asthma, may have acute episodes, when the situation worsens for short periods of time.

endoscopy. A medical procedure used to observe the inside of the body without performing major surgery. An endoscope is a long flexible tube with a lens at one end and a magnifying eyepiece at the other. To view ulcers, the lens end is inserted into the stomach and duodenum via the mouth, and light passes down the tube to illuminate the area of interest.

enzyme. A protein that acts as a catalyst. Every chemical reaction in living organisms is facilitated by an enzyme.

epidemiology. The study of diseases or conditions in human populations and the factors that influence their incidence and prevalence.

epithelial cells. Layer of cells that lines cavities, tubes and exposed surfaces of the body. Epithelial cells are often secretory in function.

duodenum. The region of the small intestine of mammals that occurs after the stomach. It is about 25 centimetres long, lined with villi and is a site for the digestion of food and absorption of nutrients.

flagella (singular flagellum). One of the ways bacteria can move is by flagella, which consist of a hollow, rigid cylinder made from the protein flagellin. A protein filament is anchored to the cell by 'hook', 'bearing' and 'rotor' structures. About 50 genes are needed to assemble a complete flagellum and supply energy to drive motility.

The filament rotates at more than 1,000 revolutions per second, driving the anticlockwise rotation of the flagellum, moving the cell forward. To change direction, the flagella stop, and then rotate in the opposite direction for a short time, causing the cells to tumble randomly. The cells can move off in another direction when the flagella start to rotate in the anticlockwise direction again. For more detailed information see Cell motility (School of Biochemistry and Molecular Biology, University of Leeds, UK).

gastric mucosa. The epithelial lining of the stomach that produces mucus.

gastritis. Inflammation of the stomach.

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

genetic variation. The variety of different types of genes in a species or population.

immune system. The cells, tissues and organs that assist the body to resist infection and disease by producing antibodies and/or altered cells that inhibit the multiplication of the infectious agent.

immunisation. The process by which the body develops the capacity to combat a specific infection. Immunisation can be induced by introducing vaccines into the body. This is more correctly called vaccination or inoculation, but the word immunisation is used to mean the same thing.

inflammation. Inflammation is the process that makes living tissue swell, become painful and turn red. Inflamed tissue contains damaged cells and has a higher than normal blood flow through it — which is why it's red and warm. It is usually 'infiltrated' by many cells of the immune system. Compounds released from damaged cells cause fluid and more inflammatory cells to leak out of the blood vessels in the area; this fluid accumulates and may make the tissue swell or block tubes. Inflammation is often associated with infection but it can also be caused by allergic reactions.

pathogen. An organism capable of causing a disease.

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. For more information see Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).

toxin. A poison, usually a protein made by a pathogenic bacteria, which is highly toxic for other living organisms. An endotoxin is contained within the bacteria and is released when the cells die or a physically damaged. An exotoxin is secreted by the bacteria into its surroundings or injected directly into cells.

ulcer. A break in the tissue lining the stomach. For more information see Stomach ulcer (Better Health Channel, Australia).

vaccine. A preparation consisting of antigens of a disease-causing organism which, when introduced into the body, stimulates the production of specific antibodies or altered cells. This produces immunity to the disease-causing organism. The antigen in the preparation can be whole disease-causing organisms (killed or weakened) or parts of these organisms.

virulent. The degree to which a disease-causing organism can affect the organism it attacks.

white blood cells. (Also known as leucocytes.) A colourless white blood cell involved in helping the body against toxins, and viral and bacterial infections. White blood cells are the immune system cells. They can be divided into many different categories on the basis of their function and appearance. There are good photographs of the different types of white blood cells at White blood cells (Puget Sound Blood Center, Washington).