A reaction that occurs when the immune system attacks a usually harmless substance (an allergen) that gains access to the body. The immune system calls upon a protective substance called immunoglobulin E (IgE) to fight these invading allergic substances (allergens). Even though everyone has some IgE, an allergic person has an unusually large army of these IgE defenders -in fact, too many for their own good. This army of IgE antibodies attacks and engages the invading army of allergic substances of allergens. As is often the case in war, innocent bystanders are affected by this battle. These innocent bystanders are special cells called mast cells. These cells are frequently injured during the warring of the IgE antibodies and the allergic substances. When a mast cell is injured, it releases a variety of strong chemicals including histamine into the tissues and blood that frequently cause allergic reactions. These chemicals are very irritating and cause itching, swelling, and fluid leaking from cells. These allergic chemicals can cause muscle spasm and can lead to lung and throat tightening as is found in asthma and loss of voice.
- Reaction, chemical
A process in which one substance is transformed into another. Thousands of different types of chemical reactions occur in the body and are essential to its structure and function.
- Reaction, desmoplastic
This term refers to the growth of fibrous or connective tissue. Some tumors elicit a desmoplastic reaction, the pervasive growth of dense fibrous tissue around the tumor. Scar tissue (adhesion) within the abdomen after abdominal surgery is another type of desmoplastic reaction. “Desmo-” comes from the Greek “desmos” meaning “a fetter or band” and “-plastic” […]
- Reactive arthritis
(1) inflamed joints; (2) inflammation of the eyes (conjunctivitis); and (3) inflammation of the genital, urinary or gastrointestinal system. Reactive arthritis is the preferred name for what was called Reiter’s syndrome since it is thought to involve the immune system which is “reacting” to the presence of a bacterial infection in the genital, urinary, or […]
- Reactive oxygen species
Species such as superoxide, hydrogen peroxide, and hydroxyl radical. At low levels, these species may function in cell signalling processes. At higher levels, these species may damage cellular macromolecules (such as DNA and RNA) and participate in apoptosis (programmed cell death).
- Reading frame
One of the three possible ways to read a nucleotide sequence in DNA, depending on whether reading starts with the first, second, or third base in a triplet.