Dictionary

base pair Two DNA bases that are complementary to one another (A and T, or G and C) and join in strands to form the double-helix that is characteristic of DNA.

base A unit of DNA. There are four bases in DNA: adenine (A), guanine (G), thymine (T), and cytosine (C). The sequence of bases (for example, CAG) constitutes the genetic code.

basal temperature 1 Usually, a person’s temperature on awakening in the morning. Because changes in basal temperature accompany ovulation, basal temperature is often tracked by women who want to ensure or avoid pregnancy. 2 A crude measure of thyroid function that is achieved by taking and comparing basal temperatures. This measure is now superceded by…

basal metabolic rate The rate of metabolism, as measured by the amount of heat given off when a person is at rest; it is expressed as calories of energy per hour per square meter of skin. The basal metabolic rate can offer clues about underlying health problems. For example, a person with an overly active…

basal ganglia A region of the base of the brain that consists of three clusters of neurons (caudate nucleus, putamen, and globus pallidus) that are responsible for involuntary movements such as tremors, athetosis, and chorea. The basal ganglia are abnormal in a number of important neurologic conditions, including Parkinson’s disease and Huntington’s disease.

basal cell carcinoma The most common type of skin cancer, which commonly presents as a sore that seems to get better and then recurs and may start to bleed. Basal cell carcinoma often occurs on the face and neck, where the skin is exposed to sunlight. These tumors are locally invasive and tend to burrow…

basal cell A small, round cell found in the lower part, or base, of the epidermis.

Bartonella quintana A parasitic microorganism in the rickettsiae family that can multiply within the gut of a louse and can then be transmitted to humans and cause trench fever. Transmission occurs when infected louse feces are rubbed into abraded skin or into the whites of the eyes. Trench fever was first recognized in the trenches…

Bartonella henselae See cat scratch disease.

Bartholin gland One of a pair of glands between the vulva and the vagina that produce lubrication in response to stimulation. Along with a second pair of nearby glands, called the lesser vestibular glands, the Bartholin glands act to aid in sexual intercourse. Also known as greater vestibular gland.

barrier method A birth control method that employs a barrier which prevents sperm from entering the cervix, thereby preventing conception. Condoms and diaphragms are examples of a barrier method. See also cervical cap; condom; condom, female; diaphragm.

Barrett esophagus A complication of chronic severe gastrointestinal reflux disease (GERD) that involves a change in the type of cells that line the inner wall of the lower esophagus. There is a small but definite increased risk of cancer of the esophagus (adenocarcinoma) in people with Barrett esophagus. The diagnosis of Barrett esophagus is made…