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Our Science Glossary glossary_a

Glossary

ADME

An acronym for Absorption, Distribution, Metabolism and Excretion. It describes the effectiveness of a pharmaceutical compound within an organism.

Agonist

A substance capable of binding to a molecular target to initiate or enhance a physiological reaction.

Alpha-4 integrin

Alpha-4 integrin is a protein on the surface of immune cells that allows them to pass into the central nervous system (CNS). In the autoimmune model of multiple sclerosis, these immune cells then mistakenly attack myelin, causing inflammation and the cascade that leads to scarring or sclerosis of the CNS. A drug which binds with the alpha-4 integrin protein will prevent the immune cell from entering the CNS. The autoimmune model then predicts that inflammation would be prevented as the immune cells would not be present in the CNS to attack myelin.

Allergic rhinitis

An allergic condition commonly known as hay-fever, which is most often characterised by nasal discharge, sneezing, and itchy, watery eyes. It affects the mucous membranes of the upper respiratory tract and the eyes and is usually caused by an abnormal sensitivity to airborne pollen. Mucus membrane is the lubricated inner lining of the nasal passages which contain mucus-secreting glands.

Allergy or allergen

A substance that causes an allergic reaction.

Amino acid

Any class of twenty molecules that are combined to form proteins in living organisms. The sequence of amino acids in a protein and hence protein function are determined by the genetic code in DNA.

Angina

Pain or discomfort caused by a lack of oxygen being supplied to the heart muscles. It may manifest as pain or discomfort, heaviness, tightness, pressure or burning, numbness aching, tingling in the chest, back, neck, throat, jaw or arms.

Angiogenesis (as in angiogenic)

The development of new blood vessels in tumours.

Antagonist

A substance capable of binding to a molecular target to neutralise or counteract a physiological reaction induced by an agonist.

Antibodies or Ig

Proteins which are produced by white blood cells as part of the immune system. They circulate in the body and attach themselves to any foreign particles (antigen) as part of the body's defence mechanism. There are five major types:

  • IgA: IgA antibodies protect body surfaces that are exposed to the outside from foreign organisms and substances. IgA antibodies are found mainly in areas of the body such the nose, breathing passages, digestive tract, ears, eyes, and vagina. This type of antibody is also found in saliva and tears. About 10% to 15% of the antibodies usually present in the body are IgA antibodies. A small percentage of people do not make IgA antibodies.
  • IgG: IgG antibodies are considered the most important antibodies for fighting bacterial and viral infections. IgG antibodies are found in all body fluids. They are the smallest but most abundant of the antibodies, normally comprising about 75% to 80% of all the antibodies in the body. IgG antibodies are the only type of antibody that can cross the placenta. Therefore, the IgG antibodies of a pregnant woman can also help protect the baby.
  • IgM: IgM antibodies are the first type of antibody produced in response to an infection and cause other immune system cells to produce compounds that can destroy invading cells. IgM antibodies are the largest type of antibody and are found in blood and lymph fluid. IgM antibodies normally comprise about 5% to 10% of all the antibodies in the body.
  • IgD: IgD antibodies appear to play a role in allergic reactions to some substances such as milk, some medications and some poisons. IgD antibodies are found in small amounts in the tissues that line the abdominal or chest cavity of the body.
  • IgE: IgE antibodies cause the body to react against foreign substances such as pollen, fungus spores, and animal dander. They are found in the lungs, skin, and mucous membranes. IgE antibody levels are often high in people with allergies.

Antigen

A molecule that binds to an antibody and is capable of stimulating or inducing specific antibodies in the body. Antigens include toxins, bacteria and foreign blood cells.

Antihistamine

A drug which acts at the histamine receptor to reduce or eliminate the effects of histamine, such as fever, itching and sneezing. Antihistamines control the symptoms of an allergic reaction by protecting tissues from some of the effects of histamine but do not stop the formation of the histamine or the allergic reaction.

Asthma

A chronic illness of the respiratory system in which the airway constricts, becomes inflamed and lined with excessive amounts of mucus, often in response to one or more triggers such as exposure to an environmental stimulant or allergen, cold air, warm air, moist air, exercise or exertion, or emotional stress. Symptoms include wheezing, shortness of breath, chest tightness and coughing. People with severe asthma live with continuous symptoms and/or experience frequent asthma attacks. These asthmatics must change their lifestyle to accommodate the condition. Overall activity levels are affected, and hospitalisation and emergency care may be frequently required.

Autoimmune disease

This disease occurs when the body experiences an immune response against its own cells and tissues. Autoimmunity is the failure of an organism to recognise its own constituent parts as "self". Any disease that results from such an aberrant immune response is termed an autoimmune disease. Prominent examples include Crohn's Disease, psoriasis, systemic lupus erythematosus, rheumatoid arthritis and diabetes mellitus type 1.