Aromatase inhibitor: A drug that inhibits the enzyme aromatase and by that means lowers the level of the estrogen estradiol. Aromatase inhibitors represent a class of antiestrogens.
Aromatase catalyzes the conversion of testosterone (an androgen) to estradiol (an estrogen) in many tissues including the adrenal glands, ovaries, placenta, testicles, adipose (fat) tissue, and brain. Estrogen is produced directly by the ovaries and is also made by the body using aromatase. Aromatase inhibitors cannot do anything about estrogen produced by the ovaries, but they do interfere with the body’s use of aromatase.
The growth of many breast cancers is promoted by estrogens. Most estrogen after menopause comes from the action of aromatase. Aromatase inhibitors may therefore be used to treat estrogen-dependent tumors after the menopause. Aromatase inhibitors are used mostly in women who have reached menopause, when the ovaries are no longer producing estrogen.
The aromatase inhibitors approved by the US Food and Drug Administration include anastrazole (Arimidex), exemestane (Aromasin), and letrozole (Femara).
Aromatherapy: A form of alternative medicine in which essential oils or other scents are inhaled to achieve therapeutic benefit. The mechanism of action in aromatherapy is unknown, but recent studies have shown that aromatherapy may be beneficial for some health problems.
- Arrector pili
Arrector pili: A microscopic band of muscle tissue which connects a hair follicle to the dermis. When stimulated, the arrector pili will contract and cause the hair to become more perpendicular to the skin surface (stand on end).
- Arrayed library
Arrayed library: In genetics, an arrayed library consists of (in technical terms) individual primary recombinant clones which are hosted in phage, cosmid, YAC, or another vector that have been placed in two- dimensional arrays in microtiter dishes (plastic dishes with an orderly array of tiny wells). Each primary clone can be identified by the identity […]
- Arrectores pilorum
Arrectores pilorum: Tiny muscles that act as the hair erector muscles. The arrectores pilorum play a key role in goose bumps, a temporary local change in the skin The chain of events leading to this skin change starts with a stimulus such as cold or fear. That stimulus causes a nerve discharge from the sympathetic […]
Arrhythmia: An abnormal heart rhythm. In an arrhythmia the heartbeats may be too slow, too rapid, too irregular, or too early. Rapid arrhythmias (greater than 100 beats per minute) are called tachycardias. Slow arrhythmias (slower than 60 beats per minute) are called bradycardias. Irregular heart rhythms are called fibrillations (as in atrial fibrillation and ventricular […]